Chapter 9, Problem 79CP

(a)

Interpretation Introduction

Interpretation:

The vinyl carbocations formed when phenyl-substituted acetylenes are protonated and the regioselectivity observed in the reaction have to be drawn and explained.

Concept Introduction:

Regioselectivity:  It is the favouring of reactants or reagents to bond to one atom or another.  Regioisomers are isomers in which connectivity of atoms varies but same numbers of atoms are present in it.  An example of reaction between propene and hydrochloric acid for regioisomers is given as,

(b)

Interpretation Introduction

Interpretation:

By relating the stabilities of transition states of vinyl carbonations, the stereo selectivity in reactions of $\text{1a-d}$ has to be explained.

Concept Introduction:

Stereoselectivity: A stereoselective reaction where only one stereoisomer reacts among mixture of stereoisomers reacts.  This reaction gives two or more stereoisomers but produces almost only one stereoisomer product.