Chapter 8, Problem 17CTQ

Interpretation Introduction

Interpretation: Whether in addition of $\text{H}-\text{X}$ to a $\pi$ bond, $\text{X}$ ends up on the carbon that forms lower or higher potential energy carbocation should be determined.

Concept introduction: The carbon-carbon double bond in alkene consists of a strong $\sigma$ bond (formed by overlap of $s{p}^2$ hybridized orbital on each carbon) and a weak $\pi$ bond (formed by overlap of pure $p$ orbital on each carbon). Due to unsaturation, alkene shows addition reaction where the double bond provides loosely held $\pi$ electrons and is readily attacked by any electron deficient group like ${\text{H}}^{+}$ ions released from acids. The loosely held $\pi$ electrons are present, therefore, behave as base though weak one.

In addition reactions of alkenes, the electrophilic and nucleophilic part of reagent may add across the double bond from opposite sides and in such case, the addition is known as anti or trans addition. The addition of reagent may occur from the same side of the double bond and in such case, the addition is known as syn or cis addition.