ISSN:
1434-4475
Keywords:
Conformational analysis
;
Lanthanide induced shift
;
NMR, coalescence
;
Optical activity
;
Rotational barrier
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Complexation of methyl 3-nitro-2-(o-tolyl)-benzoate (2, ano-trisubstituted biphenyl) with hexacarbonyl chromium gave the isomeric Cr(CO)3 complexes3 and4 both existing as two torsional isomersa andb, as seen by nmr. For the main product3 the preferred conformations of the two torsional isomersa andb were deduced by the lanthanide induced shift (LIS) technique. The activation energy for the interconversion process could be determined from kinetic measurements and especially from1H-nmr coalescence temperature of the methylsignals. The barrier of 91±1.5 kJ/mol (21.7±0.3 kcal/mol) in3 reflects the interaction of theo-H-atom of the benzene ring passing the Cr(CO)3 moiety of the benchrotrene ring during the interconversion. A partial optical resolution of3 was achieved by asymmetric reduction with a chiral lithium-aluminium hydride yielding (+)-3 with [α] D 20 +30° (benzene) and the levorotatory alcohol (−)-7.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00911932
