1H, 13C NMR studies and GIAO/DFT calculations of substituted N-(4-aryl-1-piperazinylbutyl) derivatives, new analogues of buspirone

C-13 cross-polarisation (CP) magic angle spinning (MAS) NMR data are reported for seven piperazinylbutyl derivatives of 1,4-dichloro-dibenzo[e,h]bicyclo[2,2,3]octane-2,3-dicarboimide, new analogues of buspirone (anxiolytic drug). The assignment of solid state 13C NMR spectra were made with an aid of variable contact time experiments, as well as by comparison with solution data and calculated shielding constants. C-13 CPMAS NMR spectra showed a disorder of methylene carbons in solids of 1-7, in 1 and 3 two molecules differing in conformation of n-butyl chain are probably present in the asymmetric unit cell. In CDCl3 solution, the barrier to piperazine ring inversion is 50 kJ/mol for 2, and lower than 46 kJ/mol for 1 and 3. Satisfactory agreement between the experimental chemical shifts (both in solution and solid state) and theoretical values of shielding constants (calculated by GIAO/DFT and GIAO/HF methods) was obtained (correlation coefficients R-2 > 0.98). (C) 2004 Elsevier B.V. All rights reserved.