Chapter 3, Problem 85P

Interpretation Introduction

Interpretation:

The percentage of molecules of trans-1,2-dimethycyclohexane has to be calculated.

Concept introduction:

Strain energy: Ring strain is a type of instability that exists when bonds in a molecule form angles that are abnormal.  Strain is most commonly discussed for small rings such as cyclopropanes and cyclobutanes, whose internal angles are substantially smaller than the idealized value of approximately 109°.

Angle strain of cyclic molecules: The German chemist Adolf van Baeyer, believing that all cyclic molecules like planner, proposed that the stability of a cycloalkane could be predicated by determining the difference between this ideal bond angle and the bond angle in the planner cycloalkane.

We consider the simple example of the bond angle in cyclopropane are 60⁰ degree repressing a 45.5⁰ degree it deviation from 109.5⁰, it is proved from Baeyer this deviation cause angle strain which decrease respective molecules stability.

The corresponding Bond strain formula shown below

${180}^0-\frac{{360}^0}{\text{n}}(\text{n=bond}\text{angle})$

Chair conformers: The cyclic compounds most commonly found in nature contain six-membered rings because carbon rings of that size can exist in conformation called a chair conformer that is almost completely free of ring strain.

Boat conformer: The boat conformers is further destabilized by the close proximity of the flagpole hydrogens the hydrogens at the “bow” and “stern” of the boat which cause steric strain.