New N0-alkylidene/cycloalkylidene derivatives of 5-methyl-3-phenyl-1H-indole-2-carbohydrazide: synthesis, crystal structure, and quantum mechanical calculations

The condensation products of 5-methyl-3-phenyl-1H-indole-2-carbohydrazide (1) with 2-butanone, 3-pentanone and cyclopentanone were prepared. The adducts (2a-c) were characterized by microanalysis, UV, IR, 1H NMR, 13C NMR and EI mass spectrometry. 1H NMR spectra of 2a and 2b revealed rotational restriction about the C–N bond in solution (DMSO-d6) and displayed double resonances associated with the CH3 and CH2CH3 residues of the alkylidene moieties. A variable temperature 1H NMR experiment was run on 2a to overcome the rotational barriers and thus determine the coalescence temperature but no coalescence was observed up to 77 8C. The structural analysis of 2a and 2c were also carried out by single crystal X-ray diffraction and confirmed by theoretical calculations (semiempirical PM3 and ab initio RHF/6-31G(d)). q 2005 Elsevier B.V. All rights reserved