NMR, MP2, and DFT study of thiophenoxyketenimines (o-thio-Schiff bases): Determination of the preferred form

Bahjat A Saeed; Rita S Elias; Fadhil S Kamounah; Poul Erik Hansen

doi:10.1002/mrc.4677

NMR, MP2, and DFT study of thiophenoxyketenimines (o-thio-Schiff bases): Determination of the preferred form

Magn Reson Chem. 2018 Mar;56(3):172-182. doi: 10.1002/mrc.4677. Epub 2017 Nov 29.

Authors

Bahjat A Saeed¹, Rita S Elias², Fadhil S Kamounah³, Poul Erik Hansen³

Affiliations

¹ Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah, Iraq.
² Department of Pharmaceutical Chemistry, College of Pharmacy, University of Basrah, Basrah, Iraq.
³ Department of Science and Environment, Roskilde University, Roskilde, Denmark.

PMID: 29117625
DOI: 10.1002/mrc.4677

Abstract

Five new thiophenoxyketinimines have been synthesized. ¹ H and ¹³ C NMR spectra as well as deuterium isotope effects on ¹³ C chemical shifts are determined, and spectra are assigned. DFT and MP2 calculations of both structures, chemical shifts, and isotope effects on chemical shifts are done. The combined analysis reveals that the compounds are primarily on a zwitterionic form with an NH⁺ and a S^- group and with a little of the neutral form mixed in. Very strong intramolecular hydrogen bonding is found and very high NH chemical shifts are observed. The theoretical calculations show that calculations at the MP2 level are best to obtain correct "C═S" chemical shifts.

Keywords: MP2 and DFT calculations; isotope effects on chemical shifts; tautomerism; zwitterionic form.