Investigation on the Change in C—F Stretching Vibration of FTIR Spectrum by ~1H NMR Method

FTIR spectroscopy and 1H NMR method were used to investigate three organic compounds-1,2-di[-beta-(alpha-methyl-alpha'-p-substitutephenyl) thiophene]hexafluorocyclo pentene. After assigning all main infrared spectrum peaks, it was observed that the stretching vibration frequency(v) of C-F band in cyclopentene is rised gradually, and it was found that for compound I: V(as)C-F = 1 332.21 cm(-1), v(s) C-F) = 1 231.91 cm(-1) and delta(C-F) = 1 159.9 cm(-1); for compound II : v(as)C-F = 1 338.18 cm(-1), v(s) C-F = 1 254.31 cm(-1) and delta(C-F) = 1 179.22 cm(-1); and for compound III : v(as)C-F =1 360.99 cm(-1), v(s)C-F = 1 263.29 cm(-1) and delta(C-F) = 1 194.00 cm(-1). The reason for v change is discussed not only using infrared absorption theory qualitatively but also using 1H NMR method quantitatively. It was also found that for compound I H-1 = 7.503, H-2 = 7.484; for compound II H-1 = 6.896, H-2 = 7.465; and for compound III: H-1 = 6.728, H-2 = 7.413, proveing that the substitution group -F, -OCH2CH3, -N(CH3)2 influences the C-F stretching vibration by the conjugative effect and the inductive effect. The result is satisfactory and it shows that 1H NMR is a powerful tool for infrared spectrum analysis.