Anomalous H/D Isotope Effect on (35)C1NQR Frequencies and H/D Isotope Effect on H-1 MAS NMR Spectra in Pyrrolidinium p-Chlorobenzoate

作者：Nakano Ryo; Honda Hisashi^*; Kimura Taiki; Kyo Shin shin; Ishimaru Shin'ichi; Miyake Ryosuke; Nakata Eiichi; Takamizawa Satoshi; Noro Sumiko

来源：Bulletin of the Chemical Society of Japan, 2010, 83(9): 1019-1029.

DOI：10.1246/bcsj.20090300

An anomalous isotope effect was observed in the (35)C1NQR frequency of pyrrolidinium p-chlorobenzoate (C4H8NH2+center dot C1C(6)H(4)COO(-)) by deuterium substitution of hydrogen atoms which form two kinds of N-H center dot center dot center dot O type hydrogen bonds. Large negative frequency shifts of the 35CI resonance lines, reaching 309 kHz at 77K and 267 kHz at 293K, were obtained upon deuteration, although the Cl atom in the molecule formed no hydrogen bonds in the crystal. H-1 MAS NMR lines showed significant changes by the deuterium substitution, while in contrast, small shifts of (CCP)-C-13/ MASNMR signals were obtained. Our measurements of H-1 NMR spin-lattice relaxation times (T-1) suggested that the H/D isotope shifts detected from the (35)C1NQR frequencies and 1H NMR spectra are due to structural changes rather than molecular dynamics. Single-crystal X-ray diffraction measurements showed two remarkable H/D isotope differences in the molecular arrangements, (i) the N-H length along the crystallographic a axis became I pm shorter, and (ii) the dihedral angle between benzene and the pyrrolidine ring changed by 1.1(2)degrees upon deuteration. Using density functional theory estimations, the anomalous (35)C1NQR frequency shifts and H-1 MASNMR line-shape changes could be explained by the dihedral angle change rather than the N-H length difference.

• 出版日期2010-9-15