Organic chemistry might seem overwhelming at first, but it's actually...
Chemistry330 views·Updated 27 Aug 2026·3 pagesUnderstanding AQA AS Organic Chemistry: Basics and Key Topics
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Introduction to Organic Chemistry and Naming Rules
Understanding molecular formulae is your first step into organic chemistry. You'll encounter different types: empirical (simplest ratio), molecular (actual numbers of atoms), structural (showing connections), displayed (every bond drawn), and skeletal (simplified diagrams). Think of these as different ways to describe the same molecule - like giving directions using a map versus landmarks.
Homologous series are families of compounds that share the same functional group - the bit that makes them react in similar ways. Each series has its own general formula, making it dead easy to work out molecular formulae once you know the pattern.
The IUPAC naming system follows simple rules that work like a code. Start with the stem (meth-, eth-, prop-, but-, pent-) based on carbon count, then add the ending based on the functional group (-ol for alcohols, -one for ketones, -al for aldehydes, -oic acid for carboxylic acids).
Quick Tip: Always find the longest carbon chain that includes the functional group - that's your main stem. Number carbons to give the functional group the lowest possible number.
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Isomerism - Same Formula, Different Arrangements
Structural isomers have identical molecular formulae but completely different atom arrangements. You'll spot three types: chain isomers (straight vs branched), position isomers (functional group in different spots), and functional group isomers (different functional groups entirely). It's like having the same Lego pieces but building different models.
Stereoisomers are trickier - same formula and functional groups, but atoms arranged differently in 3D space. This happens around double bonds because they can't rotate freely like single bonds.
E/Z isomerism occurs at double bonds where you compare the positions of the largest groups. Z means the big groups are on the "zame zide" (same side), while E means they're on opposite sides. For complex molecules, use CIP rules - rank the four atoms directly attached to the double bond by atomic mass, then see if the top two priorities are together (Z) or apart (E).
Memory Trick: "Z = Zame Zide" - the two highest priority groups are on the same side of the double bond.
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of 3
Reaction Mechanisms and Free Radicals
Reaction mechanisms show exactly how bonds break and form during chemical reactions. They're like step-by-step instructions for molecular transformations, helping you predict what happens when molecules collide.
Curly arrows are your best mates for showing electron movement. These arrows always show where electron pairs go - either forming new bonds or breaking existing ones. Master these, and you'll understand why reactions happen the way they do.
Free radicals are highly reactive molecules with unpaired electrons, shown with a dot. They're incredibly unstable and will react with almost anything to pair up that lonely electron. Think of them as molecular desperados looking for a partner.
Key Point: Curly arrows always show electron pair movement - never just point randomly between atoms. Follow the electrons, and you'll follow the reaction.
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Chemistry330 views·Updated 27 Aug 2026·3 pagesUnderstanding AQA AS Organic Chemistry: Basics and Key Topics
B
bv@bv
Organic chemistry might seem overwhelming at first, but it's actually just about learning how to name molecules and understand how they behave. Once you get the hang of the naming rules and can spot different types of isomers, you'll find...
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Introduction to Organic Chemistry and Naming Rules
Understanding molecular formulae is your first step into organic chemistry. You'll encounter different types: empirical (simplest ratio), molecular (actual numbers of atoms), structural (showing connections), displayed (every bond drawn), and skeletal (simplified diagrams). Think of these as different ways to describe the same molecule - like giving directions using a map versus landmarks.
Homologous series are families of compounds that share the same functional group - the bit that makes them react in similar ways. Each series has its own general formula, making it dead easy to work out molecular formulae once you know the pattern.
The IUPAC naming system follows simple rules that work like a code. Start with the stem (meth-, eth-, prop-, but-, pent-) based on carbon count, then add the ending based on the functional group (-ol for alcohols, -one for ketones, -al for aldehydes, -oic acid for carboxylic acids).
Quick Tip: Always find the longest carbon chain that includes the functional group - that's your main stem. Number carbons to give the functional group the lowest possible number.
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Isomerism - Same Formula, Different Arrangements
Structural isomers have identical molecular formulae but completely different atom arrangements. You'll spot three types: chain isomers (straight vs branched), position isomers (functional group in different spots), and functional group isomers (different functional groups entirely). It's like having the same Lego pieces but building different models.
Stereoisomers are trickier - same formula and functional groups, but atoms arranged differently in 3D space. This happens around double bonds because they can't rotate freely like single bonds.
E/Z isomerism occurs at double bonds where you compare the positions of the largest groups. Z means the big groups are on the "zame zide" (same side), while E means they're on opposite sides. For complex molecules, use CIP rules - rank the four atoms directly attached to the double bond by atomic mass, then see if the top two priorities are together (Z) or apart (E).
Memory Trick: "Z = Zame Zide" - the two highest priority groups are on the same side of the double bond.
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Reaction Mechanisms and Free Radicals
Reaction mechanisms show exactly how bonds break and form during chemical reactions. They're like step-by-step instructions for molecular transformations, helping you predict what happens when molecules collide.
Curly arrows are your best mates for showing electron movement. These arrows always show where electron pairs go - either forming new bonds or breaking existing ones. Master these, and you'll understand why reactions happen the way they do.
Free radicals are highly reactive molecules with unpaired electrons, shown with a dot. They're incredibly unstable and will react with almost anything to pair up that lonely electron. Think of them as molecular desperados looking for a partner.
Key Point: Curly arrows always show electron pair movement - never just point randomly between atoms. Follow the electrons, and you'll follow the reaction.
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