Organic Chemistry Essentials

Ever wondered why different chemicals react in such specific ways? It all comes down to their structure. Alkanes $CnH2n+2$ are saturated hydrocarbons with single bonds, while alkenes (CnH2n) have at least one double bond, making them unsaturated. You can easily test between them - alkenes turn bromine water from orange to colourless, while alkanes don't react!

Alcohols $CnH2n+1OH$ and carboxylic acids $CnH2n+1COOH$ are important functional groups. When they react together, they form esters - remember to write the carboxylic acid first in the product name (like ethyl ethanoate). In carboxylic acids, there's one less carbon in the prefix than you might expect because the carbon in the COOH group is already counted.

Crude oil forms from decomposed biomass (mainly plankton) and contains mostly alkanes. Through fractional distillation, crude oil is separated into different fractions based on boiling points. Shorter molecules have lower boiling points and are less viscous but more flammable. For molecules that are too long, cracking processes (catalytic or steam) break them down into more useful compounds.

Quick Tip! Learn your prefixes to name organic compounds easily: meth (1), eth (2), prop (3), but (4), pent (5). This system works across different functional groups!

Alkenes undergo addition reactions with halogens (like Br₂), hydrogen, and water. These reactions convert the double bond to a single bond, forming products like dibromoalkanes, alkanes, and alcohols respectively. Meanwhile, hydrocarbons can undergo complete combustion (forming CO₂ and H₂O) or incomplete combustion (forming CO) depending on oxygen availability.

Polymerisation happens in two main ways. In addition polymerisation, alkene monomers join to form large polymers without losing any atoms. In condensation polymerisation, two different monomers (each with two functional groups) react and small molecules like water are lost. Naturally occurring polymers include cellulose, starch, DNA, and proteins.