• On a molecule with a higher priority functional group, C=O is
- and -CHO is
• Aldehyde priority is higher than ketone.
4.5 Isomerism in aldehydes and ketones
• Aldehydes and ketones are constitutional isomers
• Aldehydes and ketones can have skeletal and positional isomers if there are enough carbons.
• Stereoisomers are also possible if there is a ring or C=C in the molecule
4.6 Selected Common aldehydes and ketones
• Gas at room temperature.
• Formalin is a 40% aqueous solution.
H trioxane, m.p. 62
H C H formaldehyde, b.p. -21
• Acetone and methyl ethyl ketone are important solvents.
• Formaldehyde used in polymers like
• Flavorings and additives like vanilla, cinnamon, artificial butter.
• Formaldehyde -formalin
• Acetone – solvent and metabolic product
• Vanillin - vanilla flavoring
• Benzaldehyde - almond flavor
• Cinnamaldehyde - cinnamon
• Butanedione - butter
• Boiling points – page 121
• Solubility – water solubility page 123
• More polar, so higher boiling point than comparable alkane or ether.
• Cannot H-bond to each other, so lower boiling point than comparable alcohol.
• Good solvent for alcohols.
• Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from
O-H or N-H.
• Acetone and acetaldehyde are miscible in water.
4.8 Preparation of Aldehydes and
alcohol + Na