Chapter 9, Problem 78CP

(a)

Interpretation Introduction

Interpretation:

A wedge and dash structure for each of the two lowest energy conformations of pentane has to be drawn.

Concept Introduction:

Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes.

Wedge and dash projection: In this notation two bonds are drawn in the plane of the page (sticks), one bond is drawn coming toward observer, out of the page (wedged), and one bond is drawing going away from the observer, behind the page (dashed).

(b)

Interpretation Introduction

Interpretation:

A wedge and dash structure for conformer of 3-heptyne that is analogous to anti-anti pentane has to be drawn.

Concept Introduction:

Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes.

Wedge and dash projections:  In this notation two bonds are drawn in the plane of the page (sticks), one bond is drawn coming toward observer, out of the page (wedged), and one bond is drawing going away from the observer, behind the page (dashed).

(c)

Interpretation Introduction

Interpretation:

Newman projection that illustrates the eclipsed nature of the low energy conformation of 3-heptyne has to be drawn.

Concept Introduction:

Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes.

Newman projections: The new conformations of compounds can be drawn and analyzed by Newman projections. A Newman projection visualizes different conformations of Carbon-carbon chemical bond from front to back with the front carbon represented as a black dot and the back carbon represented as a circle.

The angle between two hydrogens of a Newman projection is called as dihedral angle or torsional angle. This dihedral angle changes as the C-C bond rotates. Two conformations with special attentions are staggered and eclipsed conformation. Staggered conformation is the lowest in energy and the eclipsed conformation is the highest in energy.

For example,

Anti-conformation: The conformation with a dihedral angle of ${180}^{\circ }$ is called anti-conformation.

The two methyl groups achieve maximum separation from each other. In other, methyl groups are closer to each other; their electron clouds are repelling each other, causing an increase in energy. This unfavorable interaction is called gauche interaction.

(d)

Interpretation Introduction

Interpretation:

Newman projection that illustrates the difference between the lowest energy conformation of 3-heptyne has to be drawn.

Concept Introduction:

Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes.

Newman projections: The new conformations of compounds can be drawn and analyzed by Newman projections. A Newman projection visualizes different conformations of Carbon-carbon chemical bond from front to back with the front carbon represented as a black dot and the back carbon represented as a circle.

The angle between two hydrogens of a Newman projection is called as dihedral angle or torsional angle. This dihedral angle changes as the C-C bond rotates. Two conformations with special attentions are staggered and eclipsed conformation. Staggered conformation is the lowest in energy and the eclipsed conformation is the highest in energy.

For example,

Anti-conformation: The conformation with a dihedral angle of ${180}^{\circ }$ is called anti-conformation.

The two methyl groups achieve maximum separation from each other. In other, methyl groups are closer to each other; their electron clouds are repelling each other, causing an increase in energy. This unfavorable interaction is called gauche interaction.