Draw the structure for each of the following:

a.

b.

c.

d.

The alpha-beta unsaturated compound undergo addition- elimination or addition reaction depending upon the strength of the nucleophile or base used. The compounds undergo both the reaction if the reagent is present in excess.

The major product of the reaction is shown below.

The hydrogen bromide is the reagent used. The bromide ion undergoes conjugate addition reaction to give the product. This is because of the weak nucleophilicity of the bromide ion. Hence the product is methoxy-3-bromobutanoate.

The major product of the reaction is shown below.

The methanol is the reagent used and it undergoes direct addition to the carbonyl centre of the compound to give the direct addition product. Hence the product is an alpha-beta unsaturated ester.

The major product of the reaction is shown below.

The compound undergoes conjugate addition reaction to give the product. Since the methyl sulphide is a relative weak basic nucleophile it does not give addition reaction rapidly.

The major product of the reaction is shown below.

The ammonia is a relatively strong nucleophile and a strong base and hence it undergoes addition reaction and also the addition-elimination reaction, because the reagent ammonia is present in excess.