Hydroacridines: Part 33. An experimental and DFT study of the 13 C NMR chemical shifts of the nitrosamines derived from the six stereoisomers of tetradecahydroacridine

Francisc Potmischil; Mihaela Hillebrand; Hermann Kalchhauser

doi:10.1002/mrc.4946

Hydroacridines: Part 33. An experimental and DFT study of the ¹³ C NMR chemical shifts of the nitrosamines derived from the six stereoisomers of tetradecahydroacridine

Magn Reson Chem. 2020 Mar;58(3):249-259. doi: 10.1002/mrc.4946. Epub 2020 Jan 22.

Authors

Francisc Potmischil¹, Mihaela Hillebrand², Hermann Kalchhauser³

Affiliations

¹ Department of Organic Chemistry, Biochemistry and Catalysis University of Bucharest, Romania.
² Department of Physical Chemistry, University of Bucharest, Bucharest, Romania.
³ Institute of Organic Chemistry, University of Vienna, Vienna, Austria.

PMID: 31965644
DOI: 10.1002/mrc.4946

Abstract

The paper presents the experimental and DFT-calculated values of the ¹³ C NMR chemical shifts of the six stereoisomers of tetradecahydroacridine and of the corresponding nitrosamines. Performing the DFT calculations using several combinations of functional and basis sets, it was found that the best experimental-calculated agreement was obtained for OPBE/6-311++G (dp) method. Considering the effect of N-nitrosation upon the ¹³ C NMR chemical shifts of the C-α carbons of secondary amines, it was found that if following nitrosation both C-α carbons are shifted upfield or both are shifted downfield, then the resulted nitrosamine will have a sterically strained ─N═O group. If, however, one of the C-α is shifted upfield and the other is shifted downfield, then the ─N═O group will be strain-free or weakly strained. Our calculations predict strain energies of about 10-15 kcal mol^-1 in the first case and ≈0-6 kcal mol^-1 in the latter.

Keywords: 13C NMR; A(1,3)-strain; DFT; NMR; nitrosamines; tetradecahydroacridines.