Chemical Changes of Organic Compounds
Core ideas
Organic chemistry questions reward systematic naming and functional-group recognition. Identify the longest carbon chain containing the principal functional group; number to give that group the lowest possible locant, then double/triple bonds, then substituents. Name substituents alphabetically and use prefixes di-, tri- only for identical groups. Structural isomers share a molecular formula but differ in connectivity; cis-trans isomers require restricted rotation and two different groups on each carbon of a double bond.
Functional groups determine reactions. Alkanes undergo substitution, such as halogenation, and combustion; alkenes and alkynes undergo addition. Alcohols can be oxidized: primary → aldehyde → carboxylic acid, secondary → ketone, tertiary resistant. Carboxylic acid + alcohol ⇌ ester + water (esterification, often acid-catalyzed). Addition polymers form from alkenes; condensation polymers release a small molecule.
Traps: choosing the longest chain that does not contain the –OH or –COOH; naming an ester backwards (the alkyl group from the alcohol is named first, then the alkanoate); treating aldehydes and ketones as interchangeable; and forgetting that addition occurs at a double or triple bond while substitution occurs on saturated carbons.
Worked example: CH3–CH(OH)–CH2–CH3 has a four-carbon chain with OH on carbon 2: butan-2-ol. It is a secondary alcohol, so oxidation yields butanone, a ketone.