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13 C NMR of methyl N ‐methylthiobenzimidates . A novel approach to the interpretation of the relative 13 C‐ E / Z shifts in amides and related compounds
Author(s) -
Walter Wolfgang,
Ruback Wulf,
Meese Claus O.
Publication year - 1978
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.1270111207
Subject(s) - steric effects , chemical shift , alkyl , aryl , chemistry , interpretation (philosophy) , twist , carbon 13 nmr , stereochemistry , medicinal chemistry , computational chemistry , organic chemistry , mathematics , computer science , programming language , geometry
The 13 C NMR shifts of the E / Z mixtures of twelve, mainly ortho substituted, methyl N ‐methylthio‐benzimidates have been completely assigned. The angles of twist about the aryl‐imino‐carbon bond were determined by means of the C‐1 aryl shifts. Depending on the bulk of the ortho substituents the values vary from 18° in methyl 2‐fluoro‐ N ‐methylthiobenzibenzimidate ( Z ) to 73° in methyl 4‐bromo‐ N ,2,6‐trimethylthio‐benzimidate ( E ). An explanation for the 13 C‐ E / Z ‐ N ‐alkyl and ‐ S ‐alkyl resonances is facilitated by a new model which is initially based on the influence of electric fields. As this model is derived from amides, thioamides etc. it is possible to interpret the 13 C‐ E / Z shifts in all related classes of compounds. The role of steric compression does not seem to be as important as was previously assumed.