Organic chemistry notes

Alternative transcript:

has the lowest possible number. Numbering of the various substituents and bonds with their functional group. If there is more than one of the same type of substituent/double bond, a prefix is added showing how many there are (di - 2 tri - 3 tetra - 4 then as for the number of carbons below with 'a' added). Adding of punctuation: Commas are put between numbers (#) Hyphens are put between a number (#) and a letter Successive words are merged into one word The finalized name should look like this: #,#-di<side chain>-#-<secondary functional group>-#- <side-chain>-#,#,#-tri<secondary functional group><parent chain prefix> Order of precedence of groups: Cations> Carboxylic acids>Esters>Amide>Nitrile>Aldehyde>Ketone>Alcohol>Amines 3. Chain nomenclature Number of C atoms IC 2C Meth- Eth- prefix 3C 4C But- Prop- 5C Pent- 6C Hex- 7C 8C 9℃ Non- Hept- Oct- 10C Dec- 4. Cahn-Ingold-Prelog (CIP) rules These rules help with naming geometric isomers E/Z: 1. Compare the atomic number of the atoms directly attached to the double bond; the group having the atom of higher atomic number receives higher priority. 2. If there is a tie, we must consider the atoms at distance 2 from the double bond-as a list is made for each group of the atoms bonded to the one directly attached to the double bond. Each list is arranged order of decreasing atomic number. Then the lists are compared atom by atom; at the earliest difference, the group containing the atom of higher atomic number receives higher priority. 3. If there is still a tie step 2 is repeated for the atoms at distance 3 from the double bond. 4. If two groups differ only in isotopes, then the larger atomic mass is used to set the priority. This process is repeated recursively, each time with atoms one bond farther from the double bond, until the tie is broken. E: the higher priority groups are on opposite sides of the double bond. Z: the higher priority groups are on the same side of the double bond. Unit 1b:Intro- Spacial representation 1. Type of chemical reactions Explanation Reaction Type Addition: Combustion: is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. CH4 + 202 → 2H2O + CO2 Condensation: reaction in which two or more molecules combine to form a larger molecule, with the simultaneous loss of a small molecule such as water or methanol. CH3NH2 + CH3COOH →→ CH3NHCOCH3 + H2O Decomposition: is the process or effect of simplifying a single chemical entity into two or more fragments. 2H2O2 → 2H2O + O2 is a reaction that involves the loss of water from the reacting molecule or ion. CH5CI + NaOH → C2H4 + NaCl + H2O when an element or ion moves out of one compound and into another. It is a type of substitution reaction. Mg + 2H2O → Mg(OH)2 + H2 produces an unsaturated product by loss of atoms or groups from adjacent carbon atoms. CH5CI + NaOH → C2H4 + NaCl + H2O Dehydration: Displacement Elimination: Hydrolysis: Neutralisation reaction where two or more molecules combine to form a single product with 100% atom economy. C2H4 + Br2 →→ C2H4BR2 Redox: Substitution reaction in which a molecule of water is added to a substance a compound splits apart in a reaction involving water. Sometimes this addition causes both substance and water molecule to split into two parts. H2SO4 + H2O → H3O+ + HSO4- reaction in which an acid and a base react quantitatively with each other. NaOH + HCI → NaCl + H2O redox is a type of chemical reaction in which the oxidation states of atoms are changed. Fe2O3 + 3CO →2Fe + 3CO2 reaction during which one functional group in a chemical compound is replaced by another functional group. CH4 + Cl2 → CH3CI + HCI 2. Types of chemical formulas Chemical Formula Definition Molecular Formula (written) Empirical Formula (written) Structural Formula (drawn) Displayed Formula (drawn) Skeletal Formula (drawn) shows the actual number of atoms of each element in a molecule. shows the simplest whole number ratio of atoms of in a compound. shows the minimal detail that shows the arrangement of atoms in a molecule. shows the relative positioning of atoms and the bonds between them, all bonds shown shows only the bonds of the carbon skeleton and any functional groups. C atoms not shown, nor H atoms bonded to C atoms. STRUCTURAL ISOMERISM Same molecular formula but different structural formulae CHAIN ISOMERISM POSITION ISOMERISM 9999 FUNCTIONAL GROUP ISOMERISM Example H₂C E-trans C₂H₂O₂ C₂H₂O H H H H H H STEREOISOMERISM Same molecular formula but atoms occupy different positions in space. OH GEOMETRICAL ISOMERISM Occurs due to the restricted rotation of C=C double bonds (E/Z or trans/cis) Z-cis OH OPTICAL ISOMERISM Occurs when molecules have a chiral centre. Get two non-superimposable mirror images. Two options R/L Unit 2: Alkanes Size chain crude Boiling point Flammability Viscosity liquid +·!· bubbles of gas valve- Properties of alkanes COOL (25° C) liquid tray- flow of gas- n furnace 1.4.2: X liquid HOT (350° C) 1.4 gas liquid Short Low High - Ignites easily tertiary High - Flows easily gases (e.g.propane) boil at <40° C flow of liquid naphtha 60-100° C kerosene 175-325° C ➡diesel oil 250-350° C lubricating oil 300-370° C fuel oil 370-600° C residue (e.g. asphalt) >600° C Fractionating column H₂C H₂C-C ₂C-CH CH₂ CH₂ quaternary CH₂ -primary Long secondary High Low -Hard to ignite Zeolite structure Low - Doesn't flow well 1. Properties General formula: CnH2n+2 Properties of the alkanes, summarised to the left, are linked to the length of their chains. Between these simple molecules there are weak intermolecular forces of attraction which increase with the chain length. Alkanes are fairly unreactive but good combustibles. 2. Fractional distillation In fractional distillation: crude oil heated to about 370°C and fed into the bottom of a fractionating column, hottest at bottom, coolest at top. the vapours pass up the tower via a series of rays containing caps until they reach a tray that is cold enough to allow their condensation depending on boiling point. . at each level the fraction is piped of. lighter smaller chains rise, cool and condense at the top heavier longer chain fractions are collected at the bottom Large chain fractions are cracked producing smaller more useful fuels. 3. Cracking Cracking - breaks long chain hydrocarbons into shorter chain hydrocarbons Thermal cracking Conditions high temperature (700-1200°K) and high pressure 7000Pa. C-C bonds break forming 2 radicals that form a variety of shorter chains molecules. High proportions of alkanes are produced. Catalytic cracking Conditions 720 K, pressure just above atmospheric and Zeolite catalyst. Makes branched alkanes, cycloalkanes and aromatic compounds. 4. Combustion Complete combustion (plenty of oxygen) of alkanes produces carbon dioxide and water only, releasing large amounts of energy. Incomplete combustion (limited supply of oxygen) of alkanes produces carbon monoxide and water, with even less oxygen carbon (soot) is produced. This often happens with long hydrocarbons that need a lot of oxygen. Less energy is released. Mineral wool soaked in paraffin Zeolite Catalyst heat Laboratory catalytic cracking equipment Gaseous product (alkene) Water bath Unit 3: Pollution clean gas flue gas oxidizing gas stirrers spray tower O₂ + NO + CO + Hydrocarbons (CxHy) bottom fraction. gypsum Flue gas desulfurisation limestone Pd/Pt particles in Al2 O3 hopper circulation pump Rh particles in Al₂ O3 Catalytic converter Nz + COz + H2O 1. Pollution Combustion of all hydrocarbons may produce polluting products when burnt such as: Carbon monoxide (CO): a poison Nitrogen oxides (NOx): formed in the engine thanks to the high temperatures. These gasses can react with water to form nitric acid arising acid rain and photochemical smog. N₂(g) + O₂(g) 2NO(g) Sulphur dioxide (SO₂): produced by sulphur impurities in fuel. This gas can react with water to form sulphuric acid arising acid rain. S(s) + O₂(g) □ SO₂(g) SO₂ (s) + 0.50₂(g) + H₂O(l) H₂SO4(1) Carbon particles, called particulates, which can cause cancer and asthma. Unburnt hydrocarbons may enter the atmosphere that contribute to photochemical smog and are green house gasses. Carbon dioxide (CO₂):a green house gas. Water vapour (H₂O): a green house gas. 2. Desulfurisation The gas given out by power stations are called flue gases so the process of removing sulphur dioxide is called flue gas desulfurisation. In one method a slurry of calcium oxide (lime) and water is sprayed into the flue gas to form gypsum (calcium sulphate) that can be used to make plaster and plasterboards: Cao (s) + SO₂ (s) + 0.50₂(g) + 2H₂O(l) CaSO4 2H₂O(s) In an alternative process calcium carbonate (limestone) is used instead of calcium oxide: CaCO3 (s) + SO₂ (s) + 0.50₂(g) CaSO4 + CO₂ (g) 3. Catalytic converter The catalytic converters is a honeycomb made of ceramic coated with platinum and rhodium metals that work as catalysts. The structure allows for a high surface area to catalyse: CO (g) + NO (g)) CO₂ (g) + 2CO₂(g) And this reaction with unburned hydrocarbons (this reaction can be adapted to any hydrocarbon): C8H₁8 + 25NO 12.5N₂ +9H₂O + 8C0₂ 4. CFCs Chlorofluorocarbons (CFCs) can be damaging for the Ozone layer due to a free radical mechanism reaction where chlorine acts as a catalyst to the breakdown of ozone into oxygen. (more details about free radicals in section 4) CCl₂F₂ CCIF₂ + CI CI + 03 → CIO• + 0₂ CIO + 03 →→ CI• + 20₂ Bond enthalpy KJ/mol Unit 4: Halogenoalkanes 1. Keywords Anhydrous Initiation: Nucleophile: Propagation: Radical: Termination: ions. Ō+ H₂CC -HO: H CH3-C C-F C-CI C-Br C-I Nucleophilic Substitution of Halogenoalkanes with aqueous hydroxide H Br H H C H In the absence of water Radical forming step. Electron pair donor. Spreading of the radicals. Free radicals are reactive species with an unpaired electron and are drawn using a dot. All radicals are removed. ō- Br H3C- Elimination of Halogenoalkanes with ethanolic hydroxide ions :OH 8+ C 8+ -H CH3-C 8+ C H 8- F HIH H H C -H + Br. + H₂O Br C-OH+:Br- Polarity decreases 2. Properties General formula CnH₂n+1X where X is the halogen Halogenolakanes can be classified into: Primary have one R group attached to the carbon linked to the halogen. Secondary have two R groups attached to the carbon linked to the halogen. • Tertiary have three R groups attached to the carbon linked to the halogen. Physical properties of halogenoalkanes mainly depend on the polarity of the C-X bond. Solubility: the polarity of the bond is not enough to make halogenoalkanes soluble in water, the main intermolecular forces are Van der Walls and dipole-dipole attractions. Boiling point: - increases with increased chain length. - increases going down the halogen group. Chemical properties depend on the C-X bond strength and polarity. Reactivity increases going down the halogen group even though C-I is the least polar bond, this is due to atom size. 3 Formation Halogenoalkanes are formed via different mechanisms. Free radical substitution reaction starting from an alkane and an halogen, this reaction occurs only in the presence of UV light. Ad hv 1. 2. CH4 (g) + Cl₂ (g) □ CH3CI(g) + HCI (g) this reaction occurs in 3 steps: Initiation: breaking of the covalent bond of the halogen. Highly reactive free radicals are formed. Propagation: the free radical takes the hydrogen on the alkane to form an acid and a new alkyl radical is formed. The new radical reacts with another halogen producing an halogenoalkane and another halogen radical. H3C H CHirand CH3 ci + ci___ CH3 + HCI H3C-CI+CI H3C-CI 3. Termination: in this step free radicals react with each other. All radicals are removed. Other products are formed. CH3 H3C-CH3 CH3 From alkenes with hydrogen halides at room temperature or from alkenes reacting with halogens. C3H6+ HBr C₂H,Br C3H6+ Brl₂ C3H6Brl₂ CI-CI 4 Chemical reactions Halogenoalkanes undergo Nucleophilic substitution in the presence of a nucleophile with the halogens as the leaving group. Or elimination reaction in hot anhydrous, usually ethanolic, conditions. Unit 5: Alkenes 1. Keywords Carbocation Electrophile Electrophilic Addition of Alkenes with hydrogen bromide H H H3C H3C C I--I H H ion with a positively charged carbon atom. Electron pair accepting groups C CH3. 8- C H OSO₂OH H3C C H₂O H3C Electrophilic Addition of Alkenes with sulphuric acid H H H3C C H3C C C -:Br H H H H Br H H OSO₂OH H C C H :OSO₂OH -H -H -CH3 CH3 2. Properties General formula CnH₂n Alkene's functional group is the C=C double bonds which consists of a sigma bond and a pi bond. The pi bond lies above and below the sigma bond. There is no rotation around a double bond - resulting in geometric isomers (cis/trans E/Z) The double bond sits on a plane and the angles between each bond is roughly 120° Physical properties are very similar to those of the alkanes. Chemical properties are influenced by the double bond that had an enthalpy of 612kJ/mol (a C-C bond has a bond enthalpy of 347kJ/mol) and it is an electron rich area which can easily attract electrophiles 3. Reactions Combustion alkenes will burn in oxygen like alkanes. Electrophilic additions reactions undergo via carbocation. Main products are determined by the stability of the carbocation. • Hydrogenation - ethene reacts with hydrogen in the presence of a finely divided nickel catalyst at a temperature of about 150°C. Ethane is produced CH₂=CH₂ + H₂CH₂CH3 Uses of hydrogenation - Process used to manufacture margarine from unsaturated vegetable oils in palm and sunflower seeds. Vegetable oils = liquids, have double carbon bonds that are mostly cis- double bonds. These get converted to C-C bonds, turns liquid oils into spreadable fatty solids like margarine. Alkenes and steam - react in presence of phosphoric acid catalyst to produce alcohols. Generally reversible reaction. 570K, 65 atm pressure, C₂H₂ + H₂O CH3CH₂OH Alkenes and halogens - Cl₂ and Br₂ react rapidly at room temperature with alkenes to form dihalogenoalkanes via electrophilic addition reaction. Reaction with iodine is slower. - the reaction with bromine water is the qualitative test for alkenes. Shake alkene with bromine water, orange solution goes colourless. Alkenes with hydrogen halides -react readily at room temperature with alkenes, form halogenoalkanes. Unsymmetrical alkenes will react to produce a major and minor product. Alkenes with hydrogen halides reacts at room temperature and it is exothermic the sulfuric acid acts as a catalyst and the product is an alcohol. primary ion S+ 8- CH3-CH2 secondary ion S+ 8-8- 8+ CH3-CH-CH3 + tertiary ion S+ 8-8-8+ CH3-C- CH3 8-j* CH3 8+ Increasing stability due to positive inductive effect T-bond H C. H g-bond between carbons Unit 6: Alcohols HH I H-C-C L HH H 104.5⁰ ethanol Method Sustainability Rate of reaction Type of process HEAT Purity Percentage yield Atom economy By-products WATER OUT ALCOHOL & ACIDIFIED DICHROMATE Primary Alcohol DISTILLED PRODUCT →→→ -OH 1'alcohol Hydration of ethene Requires laboratory equipment; high level of expertise - cracking and hydration. Non-renewable Fast Continuous DISTILLATION Essentially pure, although any contaminants may be toxic 90-100% 100% WATER IN None aldehyde (excess alcohol used) + + R R-C H R₂ Secondary Alcohol 1 alcohol (excess oxidising agent used) 2° alcohol ketone HEATING UNDER REFLUX carboxylic acid Tertiary Alcohol Fermentation of sugars REACTION PRODUCT CONDENSES AND DROPS BACK IN TO PEAR-SHAPED FLASK Can be undertaken at home-fermentation Renewable Slow Batch Low, aqueous solution of alcohol is produced; can be distilled to increase ethanol content and improve purity -15% 51% Carbon dioxide - a greenhouse gas HEAT WATER OUT WATER IN ALCOHOL & ACIDIFIED DICHROMATE 1. Physical properties General formula CnH₂n+1OH Alcohols are classified into primary, secondary and tertiary based on the substitution of the carbon linked to the -OH group, like the halogenoalkanes. The -OH group allows alcohols to form hydrogen bonds. Short alcohols are soluble in water 2. Production of ethanol Ethanol is the most important alcohol in industrial chemistry since it is used as intermediate in reactions and as solvent. Ethanol can be made industrially in two ways: Hydration of ethane in the presence of phosphoric acid as catalyst (high yield, little sustainability) C₂H4+ H₂O C₂H5OH Fermentation of sugars (batch production, renewable) C6H₁2O6 (aq) 2C₂H5OH (aq) + CO₂(g) 3. Reactivity Alcohols can undergo the following reactions: -Combustion, all alcohols are flammable and can undergo complete or incomplete combustion, like alkanes. -Elimination: it is a dehydration reaction with conc sulphuric or phosphoric acid or by passing its vapours over heated aluminium oxide. · Acid catalysed elimination mechanism: alcohols → alkenes H3C- Ċ CH3 Q-H H3C- The H* comes from the H+ conc H₂SO, or conc H₂PO4 -H H CH3 H EC H+ An alkene is formed. -Oxidation: alcohols can be oxidised ins stages, usually potassium dichromate (VI) is used since its reduction into chromium (III) ions translates into a change of colour from orange to green. Partial oxidation to aldehydes (if primary alcohol) or ketones (if secondary) is done with a distillation apparatus. C₂H5OH (1) + [O] C₂H₂O(g) + H₂O(l) Complete oxidation of a primary alcohol (or aldehyde) to carboxylic acid is performed in the presence of potassium dichromate (VI) under reflux. -CH3 C₂H5OH (1) + 2[0] CH3COOH (g) + H₂O(l) Oxidation is also used as a test for alcohols or to distinguish primary alcohols from the others Substitution: alcohols undergo substitution reactions to form haloalkanes with halide ions in the presence of an acid (NaBr/H₂SO4). The order of reactivity of alcohols is 3° > 2°> 1°. The order of reactivity of the hydrogen halides is Nal > NaBr > NaCl (NaF is generally unreactive). Unit 7: The carbonyl group 1. Keywords Dipole-dipole forces attractive forces between the Electronegativity: Racemic mixture (racemate) H3C 50 CO+ O= H3C Nucleophilic Addition Mechanism CH3 :CN- H- positive end of one polar molecule and the negative end of another polar molecule CH3 is a measure of an atom's ability to attract shared electrons to itself H3C Mixture that has equal amounts of left and right-handed enantiomers of a chiral molecule. carbonyl oxygen carbonyl carbon CN Nucleophilic Addition Mechanism (Reduction) H+ from water or weak acid H+ H3C- H* from sulphuric acid -CH3 H H3C-C-CH3 CN O-H -CH3 O-H H3C-C-CH3 H : CN* CN 2. Nomenclature The carbonyl group is present in aldehydes (RCHO) and ketones (RCOR'). They are both represented by the general formula CnH₂nO. . Aldehydes (-al suffix) can only be at the end of a molecule so there is no need to provide numbering their functional group. No ketone (-one suffix) can have less than 3 carbons. So you don't need to number the carboxyl group in propanone or butanone 3. Physical properties The big difference in electronegativity between carbon and oxygen, makes the C=O bond strongly polar. There are permanent dipole-dipole forces between the molecules. Shorter chains carbonyl compounds are readily soluble in water since they form hydrogen bonds with water. As the aryl/alkyl chain lengthens solubility decreases. Methanal is a gas at room temperature. Short carbonyl compounds are liquids. 4. Reactivity Most reactions involve the C=O bond because it is strongly polar. Nucleophilic addition reaction: The reaction with NaCN and dilute HCI is very important since it increases the length of the carbon chain by one carbon. . This reaction will produce a racemic mixture (racemate) of hydroxynitriles. If performed on ethanol and followed by and hydrolysis with HCI it will produce a racemate of lactic acid. Oxidation: Aldehydes can be oxidised to carboxylic acids. Reduction (another nucleophilic addition reaction) : Many reducing agent will reduce carbonyl groups to alcohols. Once reducing agent is sodium tetrahydridoborate(III) (NaBH4) which provides a source of hydrogen to act as a nucleophile creating the H- (hydride ion). Unit 8: The carboxyl group 1. Keywords Delocalisation: Nu: 80 Charge delocalisation R Base hydrolysis OR :OH when electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. 8++ H 善 -0 H Boiling point C -H 250 200 + 3NaOH 150 100 50 131-1 OH OR 0 -100 -130 1₂0-1 + RO: 1 2 3 4 5 6 7 8 9 10 Number of carbons. R Glycerol base hydrolysis (saponification) # H Acids - Alcohols - Aldehydes Alkanes +3 Na O RO: + ROH 2. Carboxylic acids Carboxylic acids (RCOOH) have two functional groups: Carboxyl group Nomenclature: Hydroxy group Suffix: -oic acid The functional group always ends the chain and is included in carbon chain of the root name if the acid is not attached to a benzene ring. Numbering starts from the carboxyl -COOH carbon. Physical properties: Acids are able to form hydrogen bonds also in their solid states that's why they have higher boiling points than the respective alkanes. Reactivity: Due to electronegativity the -OH group in acids is more acidic than alcohols, carboxylic acids are weak acids, so they form an equilibrium when they dissociate. They undergo the same chemical reactions as any inorganic acid acting as proton donors, the carboxylate ion is stabilised by charge delocalisation. 3. Esters Nomenclature: Esters (RCOOR') are derived from the reaction between carboxylic acids and alcohols in the presence of a strong acid acting as a catalyst. The name of the esters are based on that of the parent acid but the name always begins with the alkyl or aryl group that has replaced the hydrogen of the acid; i.e. methanol + ethanoic acid methyl ethanoate Physical properties: Short esters are volatile and have pleasant fruity smells and are used in perfumes or as flavourings. They are also use as solvent and plasticisers. Fats and oils are esters with longer carbon chains. Reactivity: Formation see above. Hydrolysis to acid and alcohol: → Acidic: can occur at room temperature with a strong acid as a catalyst, the reaction does not go to completion. Base: in the presence of a base the salt of the acid is produced and the reaction goes to completion Triglycerides (animal fats and vegetable oils): Triglycerides are esters of the alcohol propane-1,2,3-triol (glycerol) and the so called "fatty acids" which are long chained (12-18) carboxylic acids. Fats are solid unsaturated and solid, vegetable oil are saturated and liquids. Fats and oils can be hydrolysed by boiling in NaOH - making glycerol and a mixture of sodium salts. The salts are called soap and are used as cleaning agents. Unit 8b: The carboxyl group 1. Keywords Delocalisation: O || CH₂ HO-C-R₁ O 11 CH HO-C-R₂ +3 CH₂OH O CH₂HO-C-R3 Triglyceride Increasing reactivity of nucleophile Ammonial NH3 Amine R'-NH₂ Alcohol R'-OH Water H₂O when electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. Methanol NaOH Catalyst R Acyl chloride R amide R- ester CH₂-O-C-R₁ N-substituted amide R CH₂-O-C-R₂ OH Biodiesel (methyl esters) I Glycerol O CH₂-O-C-R3 Increasing reactivity NH₂ O-R' carboxylic acid NHR' + CH-OH CH₂-OH Acid anhydride amide R R CH₂-OH ester N-substituted amide R NH₂ O-R' carboxylic acid OH NHR' 1. Biodiesel Biodiesel is a renewable fuel obtained from oils, mainly rape seed oil. Triglycerides are reacted with methanol in the presence of a strong alkali as a catalyst to form methyl esters and glycerol. Uses of Glycerol Glycerol is able to form many hydrogen bonds and it is very soluble in water so it has extensive applications: Used in creams and ointments to prevent their drying Solvent in the food industry, medicines and toothpastes Plasticiser. 2. Acylation (Addition- elimination reaction) Acylation is the addition of the acyl group (-COR) into another molecule. Acid derivatives all have the acyl group as part of their structure. The acid derivative is polarized and its carbonyl group can be attacked by a nucleophile, the nucleophile gets acylated. -Z -OR -CI -OCOR' Name of acid derivative It is cheaper It is less corrosive ester acyl chloride Acid derivative R general formula acid anhydride Ethanoic anhydride is used as an acylating agent over ethanoyl chloride because: It is safer as the by-product is ethanoic acid rather than hydrogen chloride. Z General formula Addition- elimination reaction depends from: The polarization of the acid derivative depends on the electron-releasing or attracting power of Z. How good Z is leaving group How good the nucleophile is. Z RCOOR’ RCOCI RCOOCOR' CH3-C0+ Example Ethyl ethanoate CH3COOC₂H5 Ethanoyl chloride, CH3COCI Nucleophilic Addition -Elimination Mechanism ō CI Ethanoic anhydride, CH3COOCOCH 3 OH H H3C- 10 CH3 + OH OH Unit 9: Aromatic compounds H₂ Benzene 2 Resonance forms Bond H + HSO → H₂SO4 C-C C---C (in benzene) C=C -CH3 Electrophilic Substitution Equation for Formation of electrophile HNO3 + 2H₂SO4 → NO₂ + 2HSO₂ + H₂O+ NO 2 NO₂* Electrophilic Substitution Equation for Formation of the electrophile. AICI + CH3COCI → CH3CO+ AICI H* + AICI → AICI + HCI NO₂ + H+ Length/nm 0.154 = Hybrid Forms C-CH3 0.140 CH3 0.134 2. Benzene - Physical properties Benzene was first isolated by Michael Faraday in 1825 and is now a major feedstock used in many industries: Polymers Pharmaceuticals Dyes Explosives. Benzene itself is highly carcinogenic. It is the simplest arene with an empirical formula of CH and a molecular formula of C6H6 . The C-C bond length in benzene is an intermediate between and C-C single bond and a C-C double bond. Benzene is more stable than the hypothetical cyclohexa-1,3,5-triene because of electron delocalisation. Each C atom has three covalent bonds - one to a H atom and the other two to C atoms. The fourth electron of each C atom is in a p-orbital. The p-orbitals overlap and the electrons in them are delocalised. This forms an area of electron density above and below the ring to form a cloud. Benzene is planar and the C-C bonds are equal in length. 2. Benzene - Reactivity Benzene combusts like other hydrocarbons and tends to produce very smoky flames. This is due to the high carbon:hydrogen ratio, this leaves a lot of carbon unburnt. Benzene have electrophilic substitution reactions in preference to addition reactions. Benzene does not discolour bromine water. Electrophilic substitution - Nitration The electrophile (NO₂+) is made in the reaction mixture of concentrated nitric acid and concentrated sulfuric acid. The overall equation for the formation of the electrophile is: H₂SO4 + HNO3 NO₂+ + HSO4 + H₂O The H+ then reacts with the HSO4 to regenerate H₂SO4 - the sulfuric acid is a catalyst. Electrophilic substitution - Friedel-Crafts acylation It uses aluminium chloride as a catalyst RCO substitutes for a hydrogen on the aromatic ring. Acyl chlorides provide the RCO group, reacting with AlCl3 RCOCI + AICI 3 RCO+ + AICI4 The aluminium chloride is then reformed by reacting with H+ from the benzene ring: AICI + H+ AICI 3 + HCI Unit 10: Amines H R R H3C- 3HN: + H H H3C-C-NH₂ H H3C N H R R 1° or 2° amine: hydrogen bond donor and acceptor Reaction with ammonia forming primary amine NH3 CH3 CH₂CH3 CH37 R CHỊCHÍNH, HỌC CHI NHCH, CHO NH3 H R H3C-C-NH3 Br H NH3 overall dipole moment → H3C-C-NH₂ + NH Br H Reaction 2 forming secondary amine The amine formed in the first reaction has a lone pair of electrons on the nitrogen and will react further with the haloalkane. → HỌC-CH2-NHCH, CH3 3° amine: hydrogen bond acceptor only H3C- H H Nucleophilic Addition -Elimination Mechanism co HỌC-CH,NH-CH-CH3 +NH,Br Diethylamine NH₂ -I 0=0 Br H3C NH₂ 1. Physical properties Amines are derivatives of ammonia, where one or more hydrogen atoms are replaced by alkyl or aryl groups. They are very reactive compounds Nomenclature Amines are classified into primary secondary and tertiary based on the number of substituents bonded to the nitrogen. If there are more than one group attached to the ammine we use N-R putting substituent in alphabetical order For secondary or tertiary amines each group from the amine group is named separately, the longest has the suffix -amine Amines are pyramidal molecules have all angles of approximately 107 degrees Short Amines are gases, longer ones are volatile liquids and have fishy smells. 2. Reactivity Preparation : by reaction of ammonia with halogenoalkanes (Nucleophilic substitution) The 10 amine can then act as a nucleophile and react with the halogenoalkane to produce a 2º amine, which can react to give a 30 amine, which in turn will react to make a 4º ammonium salt. This is not efficient. Preparation by reduction of nitriles Halogenoalkanes react with a cyanide ion in aqueous ethanol. The ion replaces the halide ion by nucleophilic substitution to form a nitrile. Step 2: RBr + CN R-CEN + Br Nitriles can be reduced to primary amines with a nickel/hydrogen catalyst. . R-CEN R-CH₂NH₂ + H₂ Electrophilic substitution (nitration) of benzene. Nitrobenzene is then reduced to phenylamine using tin and HCI as the reducing agent: Amines can act as bases Amines can accept a proton so they are weak Bronsted-Lowry bases: Alkyl groups release electrons towards the nitrogen atom, this is called inductive effect. The nitrogen is a stronger electron pair donor and so more attractive to protons. 10 alkylamines are stronger bases than ammonia because the inductive effect of the alkyl group increases the electron density on the N atom and makes it a better electron pair donor. 20 alkylamines have two inductive effects = stronger bases. 30 alkylamines = not strong because they are poorly soluble in water. Aryl groups withdraw electrons from the nitrogen atom. The nitrogen is a weaker electron pair donor and so less attractive to protons, so aryl amines are weaker bases than ammonia. Amine ca act as nucleophiles Ammonia and primary amines undergo addition-elimination reactions with acyl chlorides and acid anhydrides. Unit 11: Polymers 1. Keywords Plasticiser Atomic number: Polymers Monomer Synthesis Repeating unit Disposal a substance added to a synthetic material to produce or promote plasticity and flexibility and to reduce brittleness. number of protons (smaller no.) also the number electrons in an atom. Addition Alkene No by product Symmetrical Some are recyclable Low-density polyethylene (LDPE) (High degree of short-chain branching + Long-chain branching) Condensation With 2 functional groups HCI or H₂O Asymmetrical Biodegradable High-density polyethylene (HDPE) (Low degree of short-chain branching) Example of condensation polymerisation HOCH₂CH₂CH норс- ↓ focmemory. CH₂CH₂ OC poly(ethylene terephthalate) -COOH + 2H₂O 2. Types of polymers. Addition polymers. Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. Addition polymers are very unreactive and inert because all the non-polar single C-C bonds. Polythene chains only have van der Waal's forces between chains so are not good for forming fibres or weaving. Polyethene is very useful though as it has no branches so the chains can pack closely and hence is a strong, rigid material. LDPE is made at high temperatures and high pressures via free radical mechanism, hence it is highly branched and less packed than HDPE so it is stretcher. HDPE is made in the presence of the Ziegler-Natta catalyst at temperatures and pressures little higher than room conditions. PVC (Poly(chloroethene) contains polar C-CI bonds. This makes PVC a hard but brittle material. The properties of PVC can be modified using a plasticiser which makes the material softer and bendier. The plasticiser pushes the chains apart and the chains can slide making them more flexible. Plasticised PVC is used to make electrical cable insulation, flooring tiles and clothing. Condensation polymerisation Condensation polymerisation involves monomers with two functional groups (COOH and OH groups or COOH and NH2groups). During the condensation water or HCI is eliminated.. Condensation polymers can be hydrolysed so they are biodegradable. Common condensation polymers: Polyesters (-COO- linkage), like Terylene. - Polyamides (-CONH- linkage), like Nylon and Kevlar. - Polypeptides (-CONH- linkage), comprising all proteins. 3. Disposal of polymers. The options for disposal are either burying in landfill, burning or reusing/recycling. Advantages: reduces the amount of waste going to landfill, saving raw materials and producing less CO2 than burning the plastic. Disadvantages are that it is difficult to recycle; collecting, sorting and processing is expensive and the plastic can be easily the recycling process. Contaminated. Types of recycling: -Mechanical recycling: types of plastics are separated, washed and ground to pellets that can be melted and remoulded. -Feedstock recycling: plastics are heated to produce the monomers that can be reused to make new plastic. This can be only done a limited amount of times. Example of addition polymerisation n 101 || 1C1 monomer polymerisation (1-1). repeating unit Unit 12: Peptides 1. Keywords Denaturing Stereospecific Zwitterions (a) Primary structure Alpha-helix (c) Tertiary structure A4 destroy the characteristic properties of a biological macromolecule by heat, acidity, or other effect which disrupts its molecular conformation. preferentially interacting a particular stereoisomeric form of the substrate. molecule or ion having separate positively and negatively charged groups. a carbon R-group or side chain a hydrogen *H₂N-CH-C---O a amino group A11 Chain of amino acids OR carboxyl group Heme units Bonds- AB (b) Secondary structure (pleated sheet) (d) Quaternary structure Hemoglobin (globular protein) 2. Aminoacids There are 20 essential amino acids that make up proteins in the human body. Amino acids contain both amine (NH2) and carboxyl (COOH) functional groups. The molecule is chiral (not glycine) because it has a carbon bonded to four different groups. Most naturally occurring amino acids are the (-) enantiomer. Proteins are sequences of amino acids joined by peptide links -CONH-. (condensation reaction). Proteins can have 4 structures: . Amino acids exist as zwitterions - ions that have both a permanent positive charge and a permanent negative charge, but are neutral overall. They can act both as acids and as bases a- amino acids have the amine group on the carbon next to the -COOH group Primary structure: the sequence of amino acids along a protein chain. The structure is held together by strong covalent bonds (peptide bonds) and is therefore stable. Secondary structure: Either an a-helix or a p-pleated sheet. Held together by hydrogen bonds which are much weaker than covalent bonds. Tertiary structure: The secondary structure scan be folded into a 3-D shape. This is held together by hydrogen bonding, ionic interactions and sulphur-sulphur bonds. Quaternary structure: arrangement of two or more folded polypeptide chains that bond together with several types of bonds. Sulfur-sulfur bonds. The amino acid cysteine has a side chain with a -CH₂SH group. • When oxidised, two cysteine molecules can form a sulfur-sulfur bond that makes a bridge between the two molecules; this is called a disulfide bridge. • A double amino acid called cystine is formed. -CH₂SH + HSCH₂- + [0] -CH₂S-SCH₂ + H₂O ● 2. Denaturation The primary structure can be hydrolyzed: by boiling a protein or a peptide in HCI. The structure breaks down into a mixture of all the constituent amino acids. Hydrolysis requires 24 hours and 6 mol dm³ HCI since the covalent bond is a strong bond. Secondary structure can be disrupted by changes in pH or gentle heating (denaturing). 3. Enzymes Enzymes are biological catalysts Stereospecificity: The active site of an enzyme can be so specific that many enzymes will only catalyse reactions of one enantiomeric form of a substrate. Aminoacids with acids and bases R OH™ R + H₂N- C -COOH H₂N- C H H H+ OH™ R COO H₂N-C H* -Coo Unit 13: DNA -O O H HO O O phosphate group Guanine H H H sugar - deoxyribose NH₂ Adenine & NH NH NH₂ Guanine Guanine NH NH₂ organic base NH₂ NH₂ NH Cytosine NH ΝΗ NH₂ Thymine 1. DNA DNA = Deoxyribonucleic acid A single strand of DNA is a polymer made up from four different monomers (nucleotides): Cytosine (C) 1. 2. Thymine (T) 3. Adenine (A) 4. Guanine (G) ● . A nucleotide has three parts - a phosphate, a sugar and a base A single strand of DNA is a polymer of nucleotides linked by covalent bonds between the phosphate group of one nucleotide and the sugar of another nucleotide. Formed in a condensation reaction. The DNA Double helix is stabilised by hydrogen bonds between bases of complementary chain (A - T, C-G) 2. Anticancer drug Cisplatin is an anticancer drug works by bonding to strands of DNA (Ligand replacement reaction), distorting their shape and preventing the replication of the cells. The molecule bonds to the lone pair of nitrogen atoms on two adjacent guanine bases on a strand of DNA forming a dative covalent bonds with the platinum, displacing the Cl- ions. Side effects: It will bond to DNA in healthy cells as well as cancerous ones. H N-H H ****** ****** H-N O H-N -N H Unit 14: Infrared spectroscopy 1. Technique. Infrared depends on the fact that infrared radiation is absorbed by certain molecular bonds and this causes them to vibrate. There are three types of vibrations, symmetrical, asymmetrical and bending. . . Different bonds absorb IR radiation at different wavelengths and can be used to identify different functional groups. The finger print region is in the range 1500-500cm-1 is unique for any given compound but is too complicated to analyse. Because the finger print region is unique, compounds can be identified by comparing it to a data base of known IR spectra. IR is limited as technique because it only gives information about functional groups. Other evidence is required to determine the precise structural formula. Bending H H H asymmetrical H Symmetrica Infrared absorption data Bond N-H (amines) O-H (alcohols) C-H O-H (acids) CEN C=O C=C C-O C-C Wavenumber /cm-1 3300-3500 3230-3550 2850-3300 2500-3000 2220-2260 1680-1750 1620-1680 1000-1300 750-1100 Transmittance/% 100 100 50 0 Sample cell for solution of sample 4000 Infrared source (electrically heated filament) 3000 Reference cell for solvent only 100- Transmittance 1% OH carboxylic acid 2500-3000 cm-¹ C=C 1620 1680 cm-¹ C=O 1680-1750 cm-¹ 50 2000 OH Alcohols 3230-3550 cm-¹ 1000 N-H amines 3300 - 3500 cm-1 CH Alkane 2850 - 3330 cm -1 1500 Wavenumber/cm³ NaCl prism (or diffraction grating) 100 1000 500 Infrared detector 000 T 3000 T MMM 2000 1200 Chart recorder Wavenumber/cm-¹ 1500 wally 1000 400 Unit 15: Mass Spectrometry 1. Keywords Fragmentation m/z value vaporised sample IONISATION In MS, the process in which a molecular ion breaks into smaller ions, radicals, and/or neutral molecules. Fragments. Electron bombardment source Mass/charge value used in MS to identify peaks. An electron is knocked off each particle by the high- energy electrons to form 1+ ions Electronspray ionisation source Gaseous sample ACCELERATION Sample in volatile solvent DEFLECTION + High-energy electrons Particles gain a proton as they leave the needle moon Electron gun (hot wire filament) DETECTION Hypodermic needle attached to positive terminal of high- voltage power supply electromagnet Fine mist to vacuum pump amplifier chart recorder Positive ions are accelerated by a negative electric plate Positive ions are accelerated by a negative electric plate 2. Time of Flight Mass Spec. 1 lonisation 2 Acceleration 3 4 lon drift Detection . Sample dissolved and pushed through nozzle at high pressure and 4000v. As solvent evaporates particles gain a H+ ion + ions accelerated by -5000v electric field. Have a fixed kinetic energy Region of no electric field, so drift (lighter move faster, heavier ions slower.) + ions discharge creating a flow of electrons in the detector which registers the current and plots the mass spectrum. 3. lon sources Electron bombardment The sample being is vaporised and then high energy electrons are fired at it so it becomes ionised and lose and e-, giving a molecular ion M+ or C₂H5OH (g) C₂H5OH+ (g) + e- C₂H5OH + e- □ C₂H5OH+ + 2e- The mass lose of e- is negligible Molecular ion mass = molecular mass of compound Molecular ion detected and analysed Excess energy from ionisation can be transferred to molecular ion making it vibrate, this can cause bond to weaken and can split molecular ion into fragments - Fragmentation C₂H5OH+ (g) CH3 + CH₂OH+ (g) Molecular ion fragments are detected in MS Electronspray ionisation The sample X is dissolved in a volatile solvent and injected through a fine hypodermic needle to give a fine mist (aerosol). The tip of the needle is attached to the positive terminal of a high-voltage power supply. The particles are ionised by gaining a proton from the solvent as they leave the needle producing XH+ ions (ions with a single positive charge and a mass of Mr + 1). The solvent evaporates away while the XH+ ions are attracted towards a negative plate where they are accelerated. C₂H5OH (g) + H+ 0 C₂H5OH+ (g) Fragmentation rarely takes place 4. Fragmentation If fragmentation occurs, the peak at the highest m/z on the mass spectrum is formed by the heaviest ion that passes through the spectrometer. Unless all molecules of the original substance break up, this corresponds to the molecular ion of the sample substance. Although the molecular ion peak for 2 isomers will be the same m/z value, fragmentation patterns will be different Unit 16: NMR 1. Keywords Chemical shift (ō). No field ¹H NMR chemical shift data Type of proton ROH RCH3 RNH₂ R₂CH₂ R₂CH R-C- ||| OH R-O-C- H RCH₂Cl or Br R-C-0-C- ő H RC=C² R-C 0-H 13C NMR the resonant frequency (signal) of a nucleus relative to a standard in a magnetic field. 8/ppm 0.5-5.0 0.7-1.2 1.0-4.5 1.2-1.4 1.4-1.6 2.1-2.6 3.1-3.9 3.1-4.2 3.7-4.1 4.5-6.0 9.0-10.0 10.0-12.0 3 peaks With field NO₂ 13C NMR chemical shift data Type of carbon ----- R-C-Cl or Br R-C-N --0- c=c R-CEN O R-C- esters or R-q- acids alcohols, ethers or esters R-C- aldehydes O or ketones H3C 4 peaks NO₂ 8/ppm 5-40 10-70 20-50 25-60 50-90 90-150 1,2 dinitrobenzene 1,3 dinitrobenzene 1,4 dinitrobenzene NO₂ NO₂ NO₂ CH3 SCH3 CH3 110-125 110-160 160-185 190-220 NO₂ 2 peaks . 2. Nuclear Magnetic Resonance - theory Neutrons and protons can be found in the nucleus spinning on their own axis. In many atoms, these spins cancel each other out, but in those with an odd number of protons the nucleus itself will have an overall spin. This generates a small magnetic field around the nucleus, much like that of a bar magnet. If we place a bar magnet in an external magnetic field, it aligns parallel to it, much like a compass aligns with Earth's magnetic field. If we place nuclei with spin in a magnetic field, they, too, will align with it. If we provide the required energy, we can 'flip' the nuclei. This energy required for this can be supplied in the form of radio waves it can be recorded as a spectrum which we can then use to find information on the compound's structure. 3. Interpretation Each ¹³C or ¹H atom of a specific functional group has its own 8. Tetramethylsilane, Si(CH3)4 (TMS) is used as a standard as all the hydrogen atom are in identical environments. This means it produces a single peak, far away from most other absorption peaks. The single peak is given a chemical shift value of 0. It is also inert, non-toxic and volatile (easy to remove from the sample). The higher the electron density around the atom the higher the shielding hence the lower the 8 on the NMR spectrum. In a NMR spectrum, there is one signal (peak) for each set of equivalent 13C or ¹H atoms. . This flipping of the atom from one magnetic alignment to the other by the radio waves is known as the resonance condition. Each atom of each compound will have its specific chemical shift (ō). There are two main types of NMR: 13C NMR C-13 - Only 1% of the carbons are 13C (sensitivity problems). ¹H (proton) NMR - ¹H NMR spectra are obtained using samples dissolved in deuterated solvents or CCI4 ¹H NMR The peaks can be split into multiple smaller peaks (spin-spin coupling). These split into the number of hydrogen atoms on the adjacent carbon plus one. Following the n+1 rule. 11 The area of each peak is related to the number of H atoms producing it. The instrument produces a line called the integration trace. The relative heights of the steps show the relative number of each type of hydrogen, Equivalent Hydrogen atoms. In an H NMR spectrum, there is one signal for each set of equivalent H atoms. на H-C ∙C O H Hb Ho Ethanol has 3 groups of different hydrogen atoms a b C HỌC—CH2-CO-CH3 The peak due to group a will a tripl s it i next to b (a carbon with 2 H's) The peak due to group b will be a quartet as it is next to a (a carbon with 3H's) The peak due to group c will be a singlet as it is next to a carbon with no H's) signal appearance Split number of peaks number of neighbouring inequivalent H atoms relative size singlet 1 0 doublet IL 2 1 1:1 triplet le 3 2 1:2:1 quartet elle 4 3 1:3:3:1 Unit 17: Chromatography 1. General principles Mixture to be separated is dissolved in the mobile phase. Gas: He, N₂, H₂ 2.5 cm 3. Components separate. Stationary phase Sample injector Chromatography column R₂ 4 cm 2. Mobile phase is added throughout the process. 4. Each component is collected as it reaches T regulated oven Column: packed or open tubular (capillary) 2.5 = 0.625 Mass spectrometer detector Chromatography describes a range of separation techniques where a mixture can be separated if it is dissolved in a solvent and the resulting solution moves over a solid. The mobile phase flows through the stationary phase and carries the components of the mixture with it. It is a liquid or a gas. The stationary phase is a solid, or a liquid supported on a solid. It will hold back the components in the mixture that are attracted to it. The more affinity a component in the mixture being separated has for the stationary phase, the slower it moves with the solvent. 2. Thin layer chromatography Advantages compared to paper chromatography: Detection Once a sample has run UV or other developing agents are use to locate the spots. The distance travelled relative to the solvent is called the R, value. Faster Plates are harder wearing than paper Smaller amounts of mixtures can be separated 3. High Pressure liquid chromatography HPLC is a column chromatography performed at high pressure. Pressure drives the elution rather than gravity. . 4. Gas-liquid chromatography In Gas-liquid chromatography a column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature. . R= distance travelled by the compound distance travelled by the solvent The sample is carried by the gas and the mixture separates as some of the components move along with the gas and some are retained by the oil. Different types of detectors are used to identify the emerging gas. In GCMS (Gas Chromatography-Mass Spectrometry) a mass spectrometer is used as the detector. Chromatography Paper Thin layer Column Gas-liquid Mobile phase Solvents Solvents Solvents N₂ or He Stationary phase Paper Silica gel (SiO₂) or Alumina (Al₂O3) Silica gel (SiO₂) or Alumina (Al2O3) Powder coated with oil Support Paper Glass or plastic Column Capillary Unit 18: Test tube reactions 3. Tollens' Reagent Reagent: aqueous ammonia + silver nitrate. The active substance is the complex ion of [Ag(NH3)₂]+ Conditions: heat gently . Reaction:. The silver(1) ions are reduced to silver atom and aldehydes/alcohols oxidised. . Observation: a silver mirror forms coating the inside of the test tube. Ketones result in no change. CH3CHO + 2Ag+ + H₂O CH3COOH + 2Ag + 2H+ 4. Fehling's Solution Reagent: Fehling's Solution containing blue Cu²+ ions. Conditions: heat gently Reaction: aldehydes only are oxidised and the copper (II) ions are reduced to copper(1) oxide. Observation: Blue Cu²+ ions in solution change to a red precipitate of Cu₂O. Ketones do not react Fehling's solution. CH3CHO + 2Cu²+ + 2H₂O CH3COOH + Cu₂O + 4H+ FEHLING'S SOLUTION Contains complexed Cu²+ ions. Aldehydes reduce these ions to red copper (1) oxide. Ketones don't react with Fehling's solution. Fİ İ-İ WARM ALDEHYDE Blue Red KETONE Solution remains blue; no reaction TOLLEN'S REAGENT Contains the diamine silver ion, [Ag(NH₂)₂]. Aldehydes reduce this to metallic silver, forming a silver mirror on the glass surface. WARM WARM ALDEHYDE Colourless Silver mirror (or grey silver precipitate) KETONE Solution на s colourless: 1. Reactions Functional group Acyl chloride Alkene Aminoacids Aromatic 1 ^ry or 2^ry alcohol Aldehyde Carboxylic acid Esters Haloalkane Silver nitrate Bromine water Ninhydrin. Combustion Reagent Sodium dichromate and sulfuric acid Fehling's solution Tollens' reagent Sodium dichromate and sulfuric acid Sodium carbonate 2CH3CO2H + Na2CO3 2CH3CO2 Na + H2O + CO2 pH paper/indicator Warm with aqueous NaOH then cool then add nitric acid then add silver nitrate Result Vigorous reaction steamy fumes of HCI rapid white precipitate of AgCl Orange colour decolourises Blue-purple spot appears Smoky flames Orange to green colour change Blue solution to red precipitate Silver mirror formed Orange to green colour change Effervescence of CO2 evolved Mildly acidic solution Fruity smell White precipitate (chloroalkane) Cream precipitate (bromoalkane) Yellow precipitate (indoalkano) 2. Further observations Is the compound solid? (possible long unbranched carbon chain or ionic bonding) Is the compound liquid? (hydrogen bonds, branched carbon chain) Is the compound soluble? (can form hydrogen bond) Unit: 19 Organic synthesis 1. Keywords Atom economy: Target molecule: a measure of the percentage of reactants that become useful products. desired product of a synthetic process. 3. Chemical agents Oxidising agents: Potassium dichromate (K₂Cr₂O7) + sulphuric acid Reducing agents: Sodium tetrahydridoborate (III) (NaBrH4), will reduce C=O but not C=C Hydrogen with a nickel catalyst (H₂/Ni) will reduce C=C but not C=O Tin and hydrochloric acid (Sn/H+) will reduce nitrates to amines. Dehydrating agents: Heated aluminium oxide H+ (elimination reactions) Heat Thermometer with capillary tube strapped to it containing sample Heating oil- needs to have boiling point higher than samples melting point and low flammability 2. Reaction schemes Using organic reactions you can work out a reaction scheme to convert a starting material into a target molecule. Start by writing down the formula of the starting molecule and the target molecule. Write down all the compounds which can be made from the starting molecule and all the ways that the target molecule can be made. It is important to keep the number of steps in a reaction as small as possible and the atom economy high this increases profit and reduces waste Chemists aim to design processes that do not require a solvent and use non-hazardous starting materials as this is more sustainable and has less environmental impact. Heat →Water out condenser Water in Round bottomed flask 5. Thiele tube A Thiele tube is used to measure melting points. If impurities are present the melting point will be lowered and the sample will melt over a range of several degrees Celsius. The capillary tube is strapped to a thermometer immersed in some heating oil. Melting point can also be measured in an electronic melting point machine In both cases a small amount of the sample is put into a capillary tube. The tube is heated up and is heated slowly near the melting point 4. Reflux Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. Anti-bumping granules are added to the flask in both distillation and reflux to prevent vigorous, uneven boiling Don't draw lines between flask and condenser. . Don't have top of condenser sealed . Condenser must have outer tube for water that is sealed at top and bottom • Condenser must have two openings for water in and out that are open Electric heaters are often used to heat organic chemicals. Heat thermometer Water out Round bottomed flask It's important to be able to draw and label this apparatus accurately. Don't draw lines between flask, adaptor and condenser. Liebig condenser Water in 6. Distillation In general used as separation technique to separate an organic product from its reacting mixture. The distillate will be collected at the approximate boiling point range of the desired liquid.