Organic Chemistry and Functional Groups
Nomenclature and isomers
Organic compounds are based on carbon skeletons. Name by the longest chain, number to give the lowest locants, and identify functional group suffixes. Structural isomers share a molecular formula but differ in connectivity; this produces different physical and chemical properties.
Functional groups
Alkanes are saturated and undergo substitution with halogens under UV light. Alkenes contain C=C and undergo addition, decolourising bromine water. Alcohols contain –OH and are oxidised to aldehydes, then carboxylic acids, or to ketones if the –OH is on a secondary carbon. Carboxylic acids are weak acids that react with carbonates to release CO₂. Esters form from carboxylic acid plus alcohol with an acid catalyst and are hydrolysed by water.
Reaction types
Substitution replaces one atom or group; addition adds across a double bond; elimination removes atoms to form a double bond; condensation joins two molecules with loss of a small molecule such as water.
Traps
- Drawing an aldehyde when the alcohol is secondary.
- Confusing addition polymerisation with condensation polymerisation.
- Forgetting that alkenes are unsaturated and decolourise bromine water.
- Naming with the wrong suffix priority.
- Omitting the acid catalyst in esterification.
Rule of thumb
Identify the functional group first; it determines the reaction type. Primary alcohols oxidise to aldehydes then acids; secondary to ketones; tertiary resist oxidation.
Worked example
Propan-1-ol oxidised with acidified dichromate gives propanal on gentle heating and propanoic acid on reflux. Propan-2-ol gives propanone, which cannot be oxidised further.