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Carbon‐13 NMR Spin‐Lattice Relaxation and Molecular Motion in 2‐Phenyl‐1,3,2‐dioxarsolane and its 4‐Methyl and 4,5‐Dimethyl Derivatives
Author(s) -
Aksnes D. W.,
Ramstad K.
Publication year - 1985
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.1260230409
Subject(s) - chemistry , internal rotation , ring (chemistry) , methyl group , rotation (mathematics) , relaxation (psychology) , isotropy , activation energy , crystallography , spin–lattice relaxation , stereochemistry , computational chemistry , nuclear magnetic resonance , group (periodic table) , organic chemistry , mechanical engineering , psychology , social psychology , physics , geometry , mathematics , quantum mechanics , engineering , nuclear quadrupole resonance
13 C NMR spin‐lattice relaxation times ( T 1 ) have been measured as a function of temperature for three 2‐phenyl‐1,3,2‐dioxarsolanes. The T 1 data have been interpreted in terms of isotropic overall molecular reorientation, internal rotation about the AsPh bond and internal methyl rotation. Information on the relative order of magnitude of the overall and internal reorientations has been obtained. The internal rotation of the phenyl ring is thus 2—4 times faster than the overall molecular tumbling. Further, the internal rotation of the arsolane ring appears to be comparable to, or slightly faster than, the phenyl ring rotation. The association process which is believed to take place in the unsubstituted parent compound is reflected in its very high activation energy for overall reorientation (39 kJ mol −1 compared with 24‐25 kJ mol −1 for the methyl derivatives). The rotation of the methyl groups appears to be considerably more hindered in the cis isomer of 2‐phenyl‐4,5‐dimethyl‐1,3,2‐dioxarsolane than in the trans isomer and, in particular, the mono‐4‐methyl compound.