Synthesis, conformational studies and NBO analysis of (4-chloro-3,5-dimethyl-1H-pyrazol- 1-yl)(p-tolyl)methanone

Abstract

The title compound (3) was obtained by cyclocondensation of 4-methylbenzohydrazide (2) with 3-chloropentane-2,4-dione (1) in dry ethanol in presence of acetic acid and recrystallization from ethanol. The molecular and crystal structure of the new pyrazole derivative was determined by single crystal X-ray diffraction. It crystallizes in triclinic system with space group P-1. The molecules in the crystal adopt an anti conformation for the mutual orientation of the CO double bond with respect to the NN single bond. The pyrazole and phenyl rings are very far from being coplanar, with a dihedral angle of 49.62(4)°. Additionally, full geometry optimizations and frequency calculations were computed at the B3LYP/6-311++G(d,p) level of approximation. The NBO population analysis showed that the lpp(N1) lone pair orbital contributes to a strong resonance interactions with both adjacent π*(N2=C2) and π*(C5=C4) antibonding orbitals of the pyrazole group.