Conformation study and crystal structure of C29H25N3O3

ABSTRACT The cis stereochemistry of 6-(4-memoxy-phenyl)-l,5,7a-triphenyl-tetrahydro- imidazo [l,5-b][l,2,4] oxadiazol-2-one was studied by AMI and PM3 semi- empirical quantum mechanical models at restricted Hartree-Fock level and X-ray crystallographic analysis. It crystallizes in the monoclinic space group P2j/n with a = 10.812(1) A, b = 16.464(2) A, c = 13.379(1) A, a = 90.00°, p= 98.39(1)°, y = 90.00°, V = 2356.07(4) A 3, Z = 4, D^ = 1.3067 g/cm 3, F(000) = 976.41, u = 0.086 mm- \ The structure was solved by direct methods and refined to R(obs) = 0.066 for 1257 independent reflections [/ > 4cr(/)]. The results from X-ray diffraction were seen to be in generally consistence with theoretical calculations except for conformation of the five membered heterocyclic rings. One of the five membered rings through 02, N2, C3, N3, and C4 atoms is in twisted conformation and the other through Nl, CI, N2, C3, and C2 atoms are in envelope conformation. CI atom has maximum deviation [-0.291(5) A] from average ring plane of enveloped five membered ring. C18...C23 and C12...C17 phenyl rings are attached to the five membered ring under discussion as bisectional (neither equatorial nor axial) and equatorial respectively. 4- methoxyphenyl ring is equatorially linked to this ring, and finally, phenyl ring C24...C29 is also equatorially attached to the twisted five membered ring. Two inter- and intramolecular weak interactions in addition to two asymmetric carbon atoms were found in the structure. To investigate conformational flexibility of the title molecule, heat of formation values belonged to each conformer corresponding to certain values of selected four torsion angles were computed by varying in every 10°, after the isolated (or free) molecular structure was optimized.