21. Aldehydes and Ketones: Nucleophilic Addition

Provide a mechanism for the formation of the hemiacetals shown. [Only (c) is favored as written.]

(a)

Which of the following structures is classified as a hemiacetal?

Which of the following compounds is a hemiacetal?

Which of the following compounds is the hemiacetal formed when $\mathrm{ethanol}$ reacts with $\mathrm{propanal}$?

Draw structures of the following derivatives.

(h) the hemiacetal form of 5-hydroxypentanal

Identify the hemiacetal functional group in each of the following molecules. These molecules may not be stable enough to be the favorable product in an equilibrium reaction.

(c)

Which of the following cyclic hemiacetals would you expect to have the highest K_eq for their formation? Explain your answer.

(a)