Esters contain the ester group, COO, in which a carbonyl carbon is bonded to an oxygen atom that is joined to another carbon. The general formula is RCOOR', where RCO comes from the carboxylic acid (R can be H) and R' comes from the alcohol.Naming: the alkyl group from the alcohol is named first, then the acid part, ending in '-oate'. In a formula written RCOOR', the part joined to the C=O is the acid part.
• CH3COOCH3: methyl ethanoate
• HCOOCH2CH3: ethyl methanoate
• CH3CH2COOCH3: methyl propanoateEsters are functional group isomers of carboxylic acids. For example, methyl ethanoate and propanoic acid both have the molecular formula C3H6O2.Properties: ester molecules have no O-H bond, so they cannot hydrogen bond to each other. They therefore have lower boiling temperatures than the isomeric acids and are volatile. Small esters are slightly soluble in water, because water molecules can hydrogen bond to their oxygen atoms. Many esters have sweet, fruity smells.Uses:
• food flavourings and perfumes, because of their pleasant smells
• solvents, e.g. ethyl ethanoate in glues and nail varnish
• plasticisers, added to polymers to make them more flexibleWorked example: name CH3CH2COOCH2CH3. The acid part, CH3CH2CO, has 3 carbon atoms (propanoate). The alcohol part, CH2CH3, is ethyl. The ester is ethyl propanoate.
• CH3COOCH3: methyl ethanoate
• HCOOCH2CH3: ethyl methanoate
• CH3CH2COOCH3: methyl propanoateEsters are functional group isomers of carboxylic acids. For example, methyl ethanoate and propanoic acid both have the molecular formula C3H6O2.Properties: ester molecules have no O-H bond, so they cannot hydrogen bond to each other. They therefore have lower boiling temperatures than the isomeric acids and are volatile. Small esters are slightly soluble in water, because water molecules can hydrogen bond to their oxygen atoms. Many esters have sweet, fruity smells.Uses:
• food flavourings and perfumes, because of their pleasant smells
• solvents, e.g. ethyl ethanoate in glues and nail varnish
• plasticisers, added to polymers to make them more flexibleWorked example: name CH3CH2COOCH2CH3. The acid part, CH3CH2CO, has 3 carbon atoms (propanoate). The alcohol part, CH2CH3, is ethyl. The ester is ethyl propanoate.