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Conformational studies by nuclear magnetic resonance—IV: Restricted rotation in vinylogous thioamides
Author(s) -
Dabrowski Janusz,
KamieńskaTrela Krystyna
Publication year - 1972
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270040308
Subject(s) - chemistry , spectral line , rotation (mathematics) , alkyl , resonance (particle physics) , order (exchange) , nuclear magnetic resonance , crystallography , stereochemistry , internal rotation , atomic physics , physics , organic chemistry , geometry , mathematics , finance , astronomy , economics , mechanical engineering , engineering
Enamino ‐thial and ‐thiones R 1 C(S)CHCHNR 2 2(R 1 = H or alkyl; R 2 = Me or Et) have been shown by NMR spectra to exist in two rotational forms, s ‐ cis and s ‐ trans , the populations of the latter being approximately the same as in the case of the parent oxa analogues. An increase of the order of 2 to 4 Kcal/mole in the heights of CC and CN rotation barriers (Δ G *) was found on comparing the title compounds with their oxa analogues. IR spectra failed as a tool to establish the rotational equilibrium. IR absorption bands of the ν CC , ν CH (in the NMe 2 group) and γ HCCH vibrations have been found, but the ν CS band could not be assigned unambiguously. Anomalies concerning the frequency and intensity of the ν CC band are discussed.