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

Abstract

The vCH and 2δCH Fermi resonance doublet and unperturbed vCH and unperturbed 2δCH for 4-x-benzaldehydes increase in frequency as the mole % CHCl₃/CCl₄ increases. One portion of the vCH and 2δCH 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 v_asym. NO₂ mode occurs in the region 1533.60–1538.73 cm⁻¹ and the v_sym. NO₂ mode occurs in the region 1344.07–1345.63 cm⁻¹ for 4-nitrobenzalde-hyde in CHCl₃/CCl₄ solutions. The v_sym. NO₂ mode shifts to lower frequency by ∼4.8 cm⁻¹, while the v_sym. 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 σ_p values.