Nucleophilic attack of aldehydes and ketones

If you look in older texts, you may still see the terms hemiketal and ketal. At one time, four terms were used for the products of alcohols with carbonyl groups hemiacetal, acetal, hemiketal, and ketal. A hemiketal is now a type of hemiacetal and a ketal is now a type of acetal. Originally, acetals and hemiacetals came from aldehydes and ketals and hemiketals came from ketones. The structures of hemiacetals and acetals contained a C-H bond, but ketals and hemiketals did not. 

A dithiol provides an easier method to reduce a carbonyl group. 

Many different nitrogen-containing nucleophiles can attack a carbonyl group. In this section you consider primary amines (RNH2), secondary amines (R2NH), hydroxylamine (NH2OH), and hydrazine (NH2NH2). 

Primary amines add to aldehydes and ketones to form imines, R-N=CR2. Secondary amines react to form enamines, R 2C=CR(NR2). Hydroxylamine reacts to form an oxime, R2C=NOH. Hydrazine reacts to form a hydrazone, 

The reaction of methyl-amine with propanal to form an imine. 

---