Question

Question 40 (1 point) Reaction of an internal alkyne with excess Br2 / CH2Cl2 yields A) a tetrahalide B) a vinylic dihalide C) a vinylic tetrahalide D) a vicinal dihalide

Answer 1

Answer:

A). a tetrahalide

Explanation:

Reaction of an internal alkyne with excess Bromine Br2 in Dichloromethane CH2Cl2 solvent gives a tetrahalogenated compound compound. Here CH2Cl2 doesn't involve in reaction because it is a solvent in this reaction.

Generally Tetrahalide means compound with four number of halogen atoms, particularly Four Bromine atoms.

Hybridisation of alkyne carbon is sp hybridisation. After the reaction with Br2/CH2Cl2 those carbon atoms will have sp3 hybridisation with two Bromine atoms on each Carbon atom.

Addition of one equivalent of Br2 on alkyne generates a vicinal dibromo intermediate .

Since we are using excess equivalent of Br2 , so formed vicinal dihalide further reacts with Br2 and gives a tetrabromo compound as the major organic product.

Brz/ CH₂Cl2 General internal alkyne , reaction with excess be represented as below can Br Br Brz/CH2Cl2, Brz / CH₂Cl₂ Internal alkyne Br Br Br Vicinal dibromide tetrabromide Here vicinal indicates adjacent carbon atoms.

Why not other options ?:

Hybridisation of vinyl carbon is sp2.

As we know vinyl is often used to describe any alkenyl group (alkene - 1 H). So vinylic dihalide means two halogen atoms on sp2 hybridised carbon atom, is incorrect answer.

Vinylic tetrahalide means 4 halogen atoms on sp2 carbon , which is also incorrect answer.