Chapter 2, Problem 2.44E

(a)

Interpretation Introduction

Interpretation:

Hybridization of each atom other than hydrogen in caffeine has to be given.

Concept Introduction:

Hybridization is calculated by steric number given as follows:

  $\text{Steric number}=\left[\begin{array}{c}\left(\text{number of atoms bonded to the central atom}\right)+\\ \left(\text{number of lone pairs on the central atom}\right)\end{array}\right]$

The table that relates the steric number with hybridization is as follows:

$\begin{array}{cc}\text{Steric Number}& \text{Type of Hybridisation}\\ 2& \text{sp}\\ 3& {\text{sp}}^2\\ 4& {\text{sp}}^3\\ 5& {\text{sp}}^3\text{d}\\ 6& {\text{sp}}^3{\text{d}}^2\end{array}$

A single bond is always associated with sigma bonds. Molecules that have all atoms connected by sigma bond exclusively are stated to be in $s{p}^3$ hybridization. It has bond angle of $109.5°$. A double bond and carbocation are associated with $s{p}^2$ hybridization. It has bond angle of $120°$. A triple bond is always associated with $sp$ hybridization. It has bond angle of $180°$.

(b)

Interpretation Introduction

Interpretation:

Bond angles around each carbon and nitrogen atom in caffeine has to be estimated.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

The observed bond angles parameters in caffeine has to be compared to literature values.

Concept Introduction:

Refer to part (b).