Chapter 4, Problem 66IP

Interpretation Introduction

Interpretation:

Whether the given compounds are constitutional isomers has to be determined.

Concept Introduction:

Isomers: Compounds that have same molecular formula but different structural formula.

Constitutional isomers: The constitutional isomers are nothing but different drawing of the same compound so the name of the constitutional isomers is same.

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.