Chapter 17, Problem 66IP

(a)

Interpretation Introduction

Interpretation: Reason for why tri-tert-butylcyclobutadiene is stable has to be explained.

Concept Introduction:

• Cycloaddition reaction is a concerted addition reaction of two reactants to form a ring; in which two π-bonds are converted to two σ-bonds.
• Diels-Alder reaction is a $4+2$ cycloaddition reaction, in which a diene and dienophile undergoes a cycloaddition reaction

Steric hindrance is the crowding in a molecule due to the presence of bulky substituent. This will decreases the rate of the reaction

(b)

Interpretation Introduction

Interpretation:

Reason for why the derivative of cyclobutadiene where ${\text{R}}_{\text{1}}{\text{=R}}_3{\text{=NEt}}_{\text{2}}and{\text{R}}_{\text{2}}{\text{=R}}_{\text{4}}{\text{=CO}}_{2}Et$ is stable has to be explained.

Concept Introduction:

Resonance is an electron displacement effect for stabilizing a molecule through delocalization of bonding electrons in the pi orbital.

Delocalized electrons stabilize a compound. The extra stability gains from having delocalized electrons are called resonance stabilization or resonance energy.

Huckel’s rule states that based on the number of pi electrons planar, monocyclic, and conjugated polyene compounds can be classified as aromatic or anti-aromatic.

1. a) The number of $\pi$ electrons in a cyclic conjugated system is $4n$ where n is an integer, and then it is antiaromatic.
2. b) The number of $\pi$ electrons in a cyclic conjugated system is $\left(4n+2\right)$ where n is an integer, and then it is aromatic.

Compounds having $\left(4n+2\right)\pi$ electrons are aromatic systems that exhibit stabilization associated with aromaticity whereas $4n\pi$ electron system exhibits antiaromatic destabilization.

(c)

Interpretation Introduction

Interpretation:

Reason for why the presence of ${\text{NEt}}_{\text{2}}and{\text{CO}}_{2}Et$ groups has a destabilizing effect on $\left(4n+2\right)\pi$ system has to be explained.

Concept Introduction:

Resonance is an electron displacement effect for stabilizing a molecule through delocalization of bonding electrons in the pi orbital.

Delocalized electrons stabilize a compound. The extra stability gains from having delocalized electrons are called resonance stabilization or resonance energy.

Huckel’s rule states that based on the number of pi electrons planar, monocyclic, and conjugated polyene compounds can be classified as aromatic or anti-aromatic.

1. a) The number of $\pi$ electrons in a cyclic conjugated system is $4n$ where n is an integer, and then it is antiaromatic.
2. b) The number of $\pi$ electrons in a cyclic conjugated system is $\left(4n+2\right)$ where n is an integer, and then it is aromatic.