Infrared Study of Benzaldehyde and 4-Substituted Benzaldehydes in Carbon Tetrachloride and/or Chloroform Solutions: Aldehydic CH Group

Abstract

The vCH and 2 δCH Fermi resonance doublet and unperturbed vCH and unperturbed 2 δCH for 4- x-benzaldehydes increase in frequency as the mole % CHCl3/CCl4 increases. One portion of the vCH and 2 δCH Fermi doublet occurs in the region 2726–2746 cm−1 and the other portion of the Fermi doublet occurs in the region 2805–2845 cm−1. The unperturbed vCH for 4- x-benzaldehydes is assigned in the region 2760–2810 cm−1. Submaxima are also noted for 4- x-benzaldehydes in the region 2726–2810 cm−1 and these bands are assigned to combination tones. The vasym. NO2 mode occurs in the region 1533.60–1538.73 cm−1 and the vsym. NO2 mode occurs in the region 1344.07–1345.63 cm−1 for 4-nitrobenzalde-hyde in CHCl3/CCl4 solutions. The vsym. NO2 mode shifts to lower frequency by ∼4.8 cm−1, while the vsym. NO2 mode shifts to higher frequency by ∼1.6 cm−1 in going from CCl4 solution to CHCl3 solution. The vCN mode for 4-cyanobenzaldehyde increases in frequency in a nonlinear manner as the mole % CHCl3/CCl4 increases. The vOH mode for 4-hydroxybenzaldehyde decreases in frequency in essentially a linear manner as the mole % CHCl3/CCl4 increases. The δCH mode for 4- x-benzaldehydes increases in frequency as the mole % CHCl3/CCl4 increases; however, neither unperturbed vCH nor δCH correlates with Hammett σp values.