Aldehydes (R-CHO) & Ketones (R-CO-R′)
Both aldehydes (pictured to the right) and ketones (pictured below) contain the carbonyl group (C=O).
In nature, ketones are used by animals to send
signals; for instance, ants use 2-heptanone to warn of danger. Ants use pheromones as
sexual attractants as well. Humans also use pheromones (among various other techniques) to indicate interest in a mate.
One of the best known aldehydes is formaldehyde,
used as an antiseptic and disinfectant. It was used more often in the past. When it was determined to be toxic, it fell out of favour and was replaced by other, safer alternatives.
Acetaldehyde is used as a preservative and in the production of resins and dyes.
Physical Properties of Aldehydes & Ketones
Both aldehydes and ketones do not have the –OH group, so the melting and boiling points are lower than the corresponding alcohols.
The aldehydes and ketones do have C=O bonds, which are polar, so they are soluble in water.
Homework:
Section Questions, p. 213 # 1, 2
Section Questions, p. 217 # 1, 2 (find three), 3, 4
Answers:
