A complete model for the prediction of 1H- and 13C-NMR chemical shifts and torsional angles in phenyl-substituted pyrazoles

H-1- and C-13-NMR spectra of a number of N-phenyl- and C-phenylpyrazole derivatives have been obtained. The parameter most susceptible to changes in the dihedral angle \ theta \ is the difference delta (meta-C)-delta (ortho-C). Values for this parameter have been determined and its usefulness for conformational studies of phenyl-substituted pyrazoles has been demonstrated. A correlation between torsional angles calculated by molecular mechanics and differences in C-13 chemical shifts of the ortho and meta carbon atoms of the phenyl groups in 29 N-phenyl-substituted pyrazole derivatives and 11 C-phenyl-substituted pyrazole derivatives has been found. For the N-phenyl-substituted derivatives a correlation between torsional angles and delta (meta-H)-delta (ortho-H) values has also been demonstrated. In all cases good correlations between angles and differences in chemical shifts were observed. (C) 2001 Elsevier Science Ltd. All rights reserved.