Chapter 25, Problem 102AP

Interpretation Introduction

Interpretation:

The geometry of the carbon atoms for the given structures is to be predicted. The most nucleophilic and most electrophilic species are to be identified and the species, which react with water to give $\text{HC}{\left({\text{CH}}_3\right)}_3$, and their reactions with the help of curves arrows are to be determined.

Concept Introduction:

The VSEPR theory is used to predict the geometry of the molecules, using the number of electron pairs surrounding the central atom.

The most nucleophilic atom is the atom with the highest negative charge.

The most electrophilic atom is the atom with the highest positive charge.

Answer to Problem 102AP

Solution:

(a) The geometry of three molecules is:

(b) The most nucleophilic atom will be tert-Butyl anion ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$ and the most nucleophilic atom will be tert-Butyl cation $\text{C}{\left({\text{CH}}_3\right)}_3$.

(c) The species that reacts with water to form $\text{HC}{\left({\text{CH}}_3\right)}_3$ is ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$.

(d)

Explanation of Solution

a) The arrangement of bonds to the carton at left linear, tetrahedral, trigonal, trigonal pyramidal

The three molecules are as follows:

$\text{C}{\left({\text{CH}}_3\right)}_3$, $\text{C}{\left({\text{CH}}_3\right)}_3$, and ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$.

The geometry of tert-Butyl cation is:

The ${\text{CH}}_3{}^{+}$

molecule has a total of three electron groups around the central atom. It has three bonding electron pairs and zero nonbonding electron pairs, which arrange themselves to make a bond angle of ${120}^{\text{o}}$. This forms the geometry of type ${\text{AB}}_3$

that indicates trigonal planar geometry.

The geometry of tert-Butyl radical is:

The ${\text{CH}}_3{}^{.}$

radicals have a total of three electron groups around the central atom. It has three bonding electron pairs and one nonbonding electron pair, which arrange themselves to make a bond angle, nearly, of ${180}^{\text{o}}$. This forms the geometry of type ${\text{AB}}_3$

that indicates distorted trigonal planar geometry.

The geometry of tert-Butyl anion is:

The ${\text{CH}}_3{}^{-}$

molecule has a total of five electron groups around the central atom. It has three bonding electron pairs and one nonbonding electron pair, which arrange themselves to make a bond angle of ${107}^{\text{o}}$. This forms the geometry of type ${\text{AB}}_{\text{3}}\text{E}$

that indicates trigonal pyramidal geometry.

b) The most nucleophilic and electrophilic atom

The most nucleophilic atom is the atom with the highest negative charge.

So, the most nucleophilic atom will be tert-Butyl anion, ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$.

The most electrophilic atom is the atom with the highest positive charge.

So, the most nucleophile atom will be tert-Butyl cation, $\text{C}{\left({\text{CH}}_3\right)}_3$.

c) The species that reacts with water to give $\text{HC}{\left({\text{CH}}_3\right)}_3$.

The tert-Butyl anion has a lone pair that can pair with the proton of water, to form $\text{HC}{\left({\text{CH}}_3\right)}_3$.

Hence, the species that reacts with water to form $\text{HC}{\left({\text{CH}}_3\right)}_3$, is ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$.

The reaction of water with species which gives $\text{HC}{\left({\text{CH}}_3\right)}_3$.

d) Chemical reaction for the reaction in part (c) and curve arrow to show flow of electron.

The chemical equation for reaction of tert-Butyl anion, ${}^{-}\text{C}{\left({\text{CH}}_3\right)}_3$, with water is:

${\text{H}}_{\text{2}}\text{O}+{}^{-}\text{C}{\left({\text{CH}}_3\right)}_3\to {\text{OH}}^{-}+\text{HC}{\left({\text{CH}}_3\right)}_3$

The flow of electrons can be shown as: