Chapter 10, Problem 10.28P

Interpretation Introduction

(a)

Interpretation:

The major product for the given reaction is to be predicted, and the complete, detailed mechanism is to be drawn for it.

Concept introduction:

Terminal alkynes can be prepared from dihaloalkanes (1, 1-dihaloalkanes or 1, 2-dihaloalkanes) by treating them with a strong base via back to back E2 reaction. Three equivalents of the strong base ${\text{H}}_{\text{2}}{\text{N}}^{\text{-}}$ (${\text{NaNH}}_2$) are used to convert the dihalides into a terminal alkyne. The first two equivalents bring about two separate E2 reactions removing an acidic hydrogen and a halogen atom each time. The third equivalent of the base deprotonates the acidic proton on the newly formed terminal alkyne. Acid workup is necessary whenever the reaction conditions are strongly basic. Acid workup replaces that proton.

Interpretation Introduction

(b)

Interpretation:

The major product of the given reaction is to be predicted, and the complete, detailed mechanism is to be drawn for it.

Concept introduction:

Terminal alkynes can be prepared from dihaloalkanes (1, 1-dihaloalkanes or 1, 2-dihaloalkanes) by treating them with a strong base via back to back E2 reaction. Three equivalents of the strong base ${\text{H}}_{\text{2}}{\text{N}}^{\text{-}}$ (${\text{NaNH}}_2$) are used to convert the dihalides into a terminal alkyne. The first two equivalents bring about two separate E2 reactions removing an acidic hydrogen and a halogen atom each time. The third equivalent of the base deprotonates the acidic proton on the newly formed terminal alkyne. Acid workup is necessary whenever the reaction conditions are strongly basic. Acid workup replaces that proton.