Question

Propose mechanisms for the following reactions.

Short answer

(a)

In this reaction nucleophilic addition of methanol to carbonyl compound gives the product.

(b)

In this reaction nucleophilic addition of phenyl hydrazine to carbonyl compound gives the product.

(c)

In this reaction nucleophilic addition of phosphorus ylide to carbonyl compound gives the product.

(d)

In this reaction nucleophilic addition of water to acetal compound gives the product.

(e)

In this reaction nucleophilic addition of water to pyrrole gives the product.

(f)

In this reaction nucleophilic addition of ethyl amine to 1,1-dimethoxy cyclopentane gives the product.

Step-by-step solution

Step 1: addition of methanol

(a)

In this reaction nucleophilic addition of methanol to carbonyl compound gives the product. The H⁺ adds to the carbonyl O and making it OH⁺ and then methanol as nucleophile adds on the carbonyl carbon and open the double bond and make it as OH and in the last step methanol again adds to the carbonyl carbon and remove OH group.

Addition of Phenyl Hydrazine

(b)

In this reaction nucleophilic addition of phenyl hydrazine to carbonyl compound gives the product. The H⁺ adds to the carbonyl O and making it OH⁺ and then phenyl hydrazine as nucleophile adds onto the carbonyl carbon and open the double bond to make it as OH and in the last step hydrogen leaves leading to the formation of a a double bond between carbon and nitrogen removing OH group.

Step 3: wittig reaction

(c)

In this reaction nucleophilic addition of phosphorus ylide to carbonyl compound gives the product. It is wittig reaction. Here a four member cyclic intermediate is formed which on rearrangement gives the desired products as given.

Addition of water as nucleophile

(d)

In this reaction nucleophilic addition of water to acetal compound gives the product. The H⁺ adds to the acetal O and making it OH⁺ and then water adds as nucleophile adds on the carbon and open the bond and make it as OH and in the last step we get ketone .

Addition of water to pyrrole

(e)

In this reaction nucleophilic addition of water to pyrrole gives the product. The water is added to it as nucleophile. At the next step the lone pair of amine adds to hydrogen making it self positively charged.

Step 6: nucleophilic addition of ethyl amine to 1,1-dimethoxy cyclopentane

(f)

In this reaction nucleophilic addition of ethyl amine to 1,1-dimethoxy cyclopentane gives the product.

The nucleophilic addition of ethylamine to centre carbon of 1,1-dimethyl cyclopentane and release methoxy group takes place. Then the nitrogen donates its lone pair of electrons to form a double bond with carbon leading to the release of the second methoxy group.