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81Br/79Br‐Induced 13C Isotope Shifts and Line Broadening in the 13C NMR Spectrum of Methyl Bromide
Author(s) -
Raynes William T.,
Sergeyev Nickolai M.,
Sandor Peter,
Grayson Martin
Publication year - 1997
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/(sici)1097-458x(199702)35:2<141::aid-omr52>3.0.co;2-0
Subject(s) - chemistry , carbon 13 nmr , bromide , kinetic isotope effect , isotope , quadrupole , methyl iodide , deuterium , deuterium nmr , isotopic shift , nuclear magnetic resonance spectroscopy , bromine , computational chemistry , analytical chemistry (journal) , stereochemistry , organic chemistry , atomic physics , nuclear physics , physics
NMR studies of the 13 C isotope shift between CH 3 79 Br and CH 3 81 Br and of the linewidths of the two resolved resonances were carried out as part of a wider study of the NMR properties of methyl halide molecules. The isotope shift of 1.12 ppb can be readily accounted for in terms of the very slight shortening of the C—Br bond (0.8 Å) which occurs upon replacing 79 Br by 81 Br. From the isotope shift it is shown that the C—Br bond length derivative of the carbon‐13 shielding is ‐140 ppm Å ‐1 . There is no need to involve the change in bromine nuclear quadrupole moment to explain the isotope shift. The linewidths are influenced by scalar relaxation of the second kind and, from the observed values of 0.084 and 0.100 Hz for CH 3 79 Br and CH 3 81 Br, respectively, it is possible to deduce that J ( 13 C 79 Br)=48 Hz and J ( 13 C 81 Br) is 45 Hz. These results are in accordance with extrapolation from previously measured results for CBr 4 , CHBr 3 and CH 2 Br 2 . © 1997 by John Wiley & Sons, Ltd.