Chapter 4.12, Problem 26ATS

(a)

Interpretation Introduction

Interpretation:

Position of Adenine group and ${\text{CH}}_{\text{2}}\text{OH}$ groups in the given structure has to be depicted.

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 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.

Drawing Axial and Equatorial substituents:

Each carbon in cyclohexane can bear two substituents. One group is said to occupy an axial position, which is parallel to a vertical axis passing through the center of the ring. The other group is said to occupy an equatorial position, which is positioned approximately along the equator of the ring.

Conversion of chair conformation into Newman projection:

Ring flipping between Newman projections:

Ring flipping is a conformational change that is accomplished only through a rotation of all C-C single bonds. On ring flipping between two chair conformation equatorial changes into axial and vice-versa.

(b)

Interpretation Introduction

Interpretation:

The given Newman projection into bond-line chair form has to be converted.

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 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,

Conversion of chair conformation into Newman projection:

Ring flipping between Newman projections:

Ring flipping is a conformational change that is accomplished only through a rotation of all C-C single bonds. On ring flipping between two chair conformation equatorial changes into axial and vice-versa.