Spectral characterization and crystal structure of tetrahydropyran-4-one thiosemicarbazones

( E)-1-(Tetrahydro-3-methyl-2,6-diphenylpyran-4-ylidene) thiosemicarbazide ( 3) and ( E)-1-(2,6- bis(4-chlorophenyl)-tetrahydro-3,5-dimethylpyran-4-ylidene) thiosemicarbazide ( 4) were obtained and characterized by FT-IR, 1H NMR, 13C NMR, NOESY spectroscopy and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 3 and 4 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 4 crystallizes in the monoclinic system, space group P2 1/c, with a = 11.9645(3) Å, b = 20.0690(6) Å, c = 8.7441(2) Å, β = 105.5220(10)°, V = 2023.02(9) Å 3, and Z = 4. Compounds 3 and 4 exist in chair conformation with equatorial orientation of all the substituents at pyran ring except the methyl group at C-5 of compound 4 which is oriented at axial disposition to stabilise the chair conformation and the configuration about the C N double bond is syn to C-5 carbon ( E-form).