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Carbon‐13 NMR studies of multicyclic lactams. Structures and 13 C assignments by lanthanide induced shifts, relaxation studies and MINDO/3 calculations
Author(s) -
Barfield Michael,
Babaqi Abdulla S.
Publication year - 1987
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.1260250512
Subject(s) - mindo , chemistry , lanthanide , relaxation (psychology) , chemical shift , carbon 13 nmr , computational chemistry , dipole , carbon fibers , resonance (particle physics) , crystallography , molecule , stereochemistry , organic chemistry , atomic physics , ion , social psychology , psychology , materials science , physics , composite number , composite material
Carbon‐13 NMR studies were performed with a series of nineteen multicyclic lactams. The solution conformations of most of these were determined using the lanthanide induced shift (LIS) method in combination with x‐ray and/or MINDO/3 optimized geometries. These analyses show that E ‐caprolactam and 3‐azabicyclo[4.3.1]decan‐4‐one have at least two conformations in solution. The LIS structural analyses were further confirmed by means of 13 C T 1 relaxation times with Gd(dpm) 3 and Gd(fod) 3 as relaxation reagents. However, relaxation data for carbons in proximity to the complexation site are not reliable for this purpose, probably because of the occurrence of mechanisms other than dipole‐dipole. It is also noted that it is better to compare carbons having the same number of bonded hydrogens. With the help of the LIS data it was possible to assign unambiguously the chemical shifts of the carbons in all of the lactams in this study.