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Substitution effects in the 15 N NMR chemical shifts of heterocyclic azines evaluated at the GIAO‐DFT level
Author(s) -
Semenov Valentin A.,
Samultsev Dmitry O.,
Krivdin Leonid B.
Publication year - 2018
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4731
Subject(s) - chemical shift , chemistry , computational chemistry , carbon 13 nmr , tetrazine , series (stratigraphy) , stereochemistry , organic chemistry , paleontology , biology
A systematic study of the accuracy factors for the computation of 15 N NMR chemical shifts in comparison with available experiment in the series of 72 diverse heterocyclic azines substituted with a classical series of substituents (CH 3 , F, Cl, Br, NH 2 , OCH 3 , SCH 3 , COCH 3 , CONH 2 , COOH, and CN) providing marked electronic σ‐ and π‐electronic effects and strongly affecting 15 N NMR chemical shifts is performed. The best computational scheme for heterocyclic azines at the DFT level was found to be KT3/pcS‐3//pc‐2 (IEF‐PCM). A vast amount of unknown 15 N NMR chemical shifts was predicted using the best computational protocol for substituted heterocyclic azines, especially for trizine, tetrazine, and pentazine where experimental 15 N NMR chemical shifts are almost totally unknown throughout the series. It was found that substitution effects in the classical series of substituents providing typical σ‐ and π‐electronic effects followed the expected trends, as derived from the correlations of experimental and calculated 15 N NMR chemical shifts with Swain–Lupton's F and R constants.