Chapter 7.8, Problem 30CC

Interpretation Introduction

Interpretation: The protic and aprotic nature for the given solvents should be classified.

Concept Introduction:

Protic solvent: solvents that contains ${\text{H}}^{+}$ bonded to electronegative atom.

Aprotic solvent: they do not contain ${\text{H}}^{+}$ directly bonded to the electronegative atom.

Electronegativity: it is the ability of atom to attract a lone pair of electrons towards itself in a substrate. Electronegativity property follows the trend that it increases across the periods and decreases down the column in the periodic table.

Carbocation: it is carbon ion that bears a positive charge on it.

Primary carbocation < secondary carbocation < tertiary carbocation

Leaving group: it is a fragment that leaves substrate with a pair of electrons via heterolytic bond cleavage.

Nucleophile: donates pair of electrons to positively charged substrate resulting in the formation of chemical bond.

${\text{S}}_{\text{N}}2$Reaction: It is a nucleophilic substitution reaction in which the rate determining step depends on both of the molecules involved. The bond making and the bond breaking process happens simultaneously in this reaction.

Structure of the substrate plays major role in the reactivity of ${\text{S}}_{\text{N}}2$ reaction. If the substrate is more substituted then the rate of the reaction will becomes slower. Since the mechanism of ${\text{S}}_{\text{N}}2$ reaction proceeds through backside attack on the substrate, it depends on steric factor that if more groups attached near the leaving group the reactivity becomes slower. Hence, primary substrate favors ${\text{S}}_{\text{N}}2$ mechanism. The ${\text{S}}_{\text{N}}2$ reactivity increases in molecule with better leaving group and strong nucleophile.