NMR relaxation by the antisymmetric component of the shielding tensor: a longer transverse than longitudinal relaxation time

✍ Scribed by Frank A.L. Anet; Daniel J. O'Leary; Charles G. Wade; Robert D. Johnson

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 479 KB
• Volume: 171
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(90)85237-7

✦ Synopsis

The first experimental detection of an antisymmetrical component (u') in the NMR shielding tensor of a nucleus is reported. The 13C NMR relaxation rates ( I /T, and 1 /T,) of the ethyledic carbons in tetrachlorocyclopropeene in toluene-d, at about -90°C are dominated at high fields by the shielding tensor modulated by random molecular rotation. We find that T2 is circa 1.1 T, in contrast to that in "CS*, where u' is zero by symmetry and where the measured Tz is not greater than the maximum (O.S57r, ) allowed for this case. The present results are in qualitative agreement with previous ab initio IGLO calculations showing thaf the ethylenic carbons in cyclopropenes have unusually large antisymmetric components in their shielding tensors.