Crystal and single molecule structures of N-phenacyl-4-cyanopyridinium bromide

The crystal structure of N-phenacyl-4-cyanopyridinium bromide, C6H5–CO–CH2–NþC5H4–CN·Br2, was determined by X-ray diffraction as monoclinic, space group C2/c with a ¼ 20:910ð4Þ, b ¼ 12:849ð3Þ, and c ¼ 9:934ð2Þ A° , b ¼ 90:79ð3Þ8: The dihedral angle between the planes of the phenyl and pyridine rings is 84.68(14)8; the C ; N group is coplanar with pyridine, while the CyO group is at 2.4(4)8 to the phenyl ring. The difference in the geometry of C ; N substituent between N-phenacyl-4-cyanopyridinium bromide and 4-cyanopyridine in crystals reveals that quaternization of pyridine ring lowers the mesomeric interaction between the ring and electronwithdrawing substituent. The optimized geometry at B3LYP approach is in good agreement with the X-ray data, except the conformation of the chain between rings, which is planar in the crystal but folded in the single molecule. The screening constants for 1H and 13C atoms have been calculated by GIAO/B3LYP/6-31G(d,p) and analyzed. A linear correlation between the experimental 13C chemical shifts and the computed screening constants has been obtained. Protons at a-positions to nitrogen atom are outside the linear correlation. q 2004 Elsevier B.V. All rights reserved.