The title compounds, 1-[2-(5-methyl-2-benzoxazolinone-3-yl)acetyl]-3-phenyl-5-(3,4-dimethoxyphenyl)-4,5-dihydro-1H-pyrazole (5a) and 1-[2-(5-chloro-2-benzoxazolinone-3-yl)acetyl]-3-phenyl-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazole (5b), were synthesized. The crystal and molecular structures of 5a and 5b have been determined by elemental analyses. IR, H-1 NMR, ESI-MS and single-crystal X-ray diffraction. Molecular geometries of 5a and 5b in the ground state have been calculated using the density functional method (DFT) with B3LYP/6-31G(d,p) basis set and compared with the experimental data. In addition, the molecular electrostatic potential maps and frontier molecular orbitals of 5a and 5b were performed. (C) 2011 Elsevier B.V. All rights reserved.