H-1 C-13 NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5-endo,6-exo,8,9,9,10, 10-octachloro-2-bornene and their DFT/GIAO C-13 chemical shifts

摘要

The H-1 and C-13 NMR chemical shifts for six toxaphene congeners: 2-exo,3-endo,6-exo,8,9,10-hexachloro- (1), 2-exo,3-endo,5-exo,9,9,10, 10-heptachloro- (2), 2-exo,3-endo,6-exo,8,9, 10, 10-heptachloro- (3), 2-exo,3-endo,5-exo,6-endo,8,9, 10-heptachloro- (4), 2-exo,3-endo,5-exo, 6-etido,8.9.9,10-octachlorobornane (5) and 2,5-endo,6-exo,8,9,9,10,10-octachloro-2-bornene (6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) H-1,H-1 correlation spectroscopy (COSY), PFG H-1. C-13 Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H, 13 C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers (6a,6b) were elucidated by ab initio MO method and single point DFT/GlAO calculations for C-13 chemical shifts. Theoretical calculations proved that the single crystal structure of 6 cot-responds its most stable conformer in solution. (c) 2005 Elsevier B.V. All rights reserved.