Ab InitioStudy of Atropisomers of Derivatives ofN-Benzyl-2-phenylpyridinium Ions

Firouzeh Nemati,Hossein Kiani

doi:10.1155/2012/297582

Abstract

Ab initiocalculation at RHF/6-31G*level of theory for geometry optimization of conformers ofN-benzyl-2-phenylpyridinium ions are reported. The series of electron-withdrawing and electron-donating groups have been replaced by 3-H phenyl and benzyl ofN-benzyl-2-phenylpyridinium ions and the energy difference between thesyn- andanti- forms discussed in terms of π-π stacking.

Highlights

Atropisomers are stereoisomers resulting from hindered rotation about single bonds where the barrier to rotation is high enough to allow the isolation of the conformational isomers[1]
For model 1, we have found two minima, one splayed and one stacked conformer (Figure 2)[11]
Phenyl and benzyl ring polarized by electron-donating substituent (-OMe) which caused increasing the π- electron repulsion[2]

Summary

Introduction

Atropisomers are stereoisomers resulting from hindered rotation about single bonds where the barrier to rotation is high enough to allow the isolation of the conformational isomers[1]. Our studied showed that in these models, dihedral angles of N1-C2-C7-C8 change between +73 to +289 o (or -71o) in stacked anti-conformers and +100 to 109o in stacked synconformers to make π-π interaction possible between two rings. Model 3 (with –OMe as an electrondonating substitution in both rings) does not stack in anti-conformer. Phenyl and benzyl ring polarized by electron-donating substituent (-OMe) which caused increasing the π- electron repulsion[2].

Results

Conclusion