Chapter 12, Problem 12.62P

Interpretation Introduction

Interpretation:

The missing compounds in the given synthesis scheme are to be supplied.

Concept introduction:

Alkene shows electrophilic addition reaction with molecular halogen to form a vicinal dihalide as the product. The first step of this reaction is the formation of the halonium ion intermediate. The next step is the attack by the halide anion on one of the carbons from the initial double bond. This leads to the formation of a vicinal dihalide. Since a cyclic halonium ion intermediate is formed, the second halogen atom can only attack from the side opposite to this ring resulting in a trans addition of molecular halogen across the double bond.

A dihaloalkane (geminal or vicinal) having at least one hydrogen atom on the same carbon undergoes dehydrohalogenation reaction when treated with an excess of a strong base to form an alkyne via an E2 reaction. An alkynide anion is formed if the product is a terminal alkyne because of the presence of the excess strong base. An acidic workup is needed to get the uncharged alkyne.

Alkynes, on oxymercuration-reduction reaction, add only one molecule of water to initially produce an enol which tautomerizes to the more stable aldehyde or ketone.

Bromine, in acetic acid, is used for the bromination of the $\text{α}$-carbon of carbonyl compounds. Only one bromine is added in this case.

Alkenes, on treatment with aqueous bromine, give bromohydrin as the product.