Studies in stereochemistry

Abstract

The thesis entitled “Studies in Stereochemistry” is divided into three parts:

Part I This part describes attempts to understand the cause of the unusual conformational preference of cyclohexane-1,4-dione. It is divided into three chapters:

Chapter 1: A brief review of the conformational analysis of cyclohexane-1,4-dione and its derivatives. Chapter 2: Describes the synthesis of three 2,5-bridged cyclohexane-1,4-diones. Their dipole moments and NMR spectra clearly establish that the cyclohexane-1,4-dione moiety exists in a twist conformation in all these compounds. The cause of conformational preference in cyclohexane-1,4-dione has been discussed in light of these observations. It has been attributed in this thesis to the greater hyperconjugation of bonds with the carbonyl group in the twist form relative to the chair form. Chapter 3: Deals with attempts to prepare tetramethyl tetrabromocyclohexane-1,4-dione. A comparison of the total potential energy of various possible conformers of this compound has been made using: (a) Kitaigorodsky potential function (I) for non-bonded interactions (b) Potential function (II) for electrostatic interactions (c) The usual three-fold cosine function (III) for torsional strain

Part II This part is divided into two chapters (Chapters 4 and 5):

Chapter 4: A review of stereochemical aspects of eight-membered rings. Various physicochemical methods, including energy minimization calculations, have been briefly discussed. Chapter 5: Describes work on the stereochemistry of three eight-membered heterocyclic compounds, viz., N,N-disubstituted-1,5-dithia-3,7-diazacyclooctanes and their bromo and methyl derivatives. The dipole moments of these compounds have been determined. Theoretical dipole moments evaluated using vectorial addition of group moments for the crown conformation with substituents in equatorial positions agree with experimental values. A comparison of the total potential energies of various conformations of 1,5-dithia-3,7-diazacyclooctane has also been reported.

Part III

Chapter 6: Describes attempts to prepare and resolve a cis-decalin derivative, expected to be optically active due to molecular dissymmetry.

Appendix The appendix describes the method developed during this work by modifying literature methods for calculating dipole moments by vectorial addition of group moments. A flowchart of the computer program used in the calculation of total potential energy of a conformation is also provided.