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The static and Dynamic NMR spectra of 4,4′‐bis( N ‐isopropyl‐ N ‐nitrosoamino)biphenyl, a four‐site exchange problem
Author(s) -
Grindley T. Bruce,
Lu MuJian,
Colpa Johannes P.,
Wu ShiMing,
Buncel Erwin
Publication year - 1986
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.1260240705
Subject(s) - chemistry , isopropyl , nmr spectra database , biphenyl , nitroso , spectral line , crystallography , carbon 13 nmr , group (periodic table) , nuclear magnetic resonance spectroscopy , stereochemistry , carbon 13 nmr satellite , medicinal chemistry , fluorine 19 nmr , organic chemistry , physics , astronomy
The 1 H and 13 C NMR spectra of 4,4′‐bis( N ‐isopropyl‐ N ‐nitrosoamino)biphenyl at 22°C were consistent with the presence of three isomers due to slow rotation about the N—N bonds of the two N ‐nitroso groups. The structures of the three isomers were assigned by means of their symmetries and from the known effects of the two orientations of the N ‐nitroso group on 1 H and 13 C NMR chemical shifts. Each conversion of an N ‐nitroso group from anti to syn to an aryl group was associated with the same free energy difference (0.26 kcal mol −1 ) after symmetry corrections were made. The changes in the 13 C NMR spectra recorded from 95 to 150°C were simulated using a program for classical four‐site exchange. The potential barrier to rotation was calculated to be 20.76±0.06 kcal mol −1 at 400 K.