Abstract

The <i>v</i>CH and 2δCH Fermi resonance doublet and unperturbed <i>v</i>CH and unperturbed 2δCH for 4-<i>x</i>-benzaldehydes increase in frequency as the mole % CHCl₃/CCl₄ increases. One portion of the <i>v</i>CH 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 <i>v</i>CH for 4-<i>x</i>-benzaldehydes is assigned in the region 2760-2810 cm⁻¹. Submaxima are also noted for 4-<i>x</i>-benzaldehydes in the region 2726-2810 cm⁻¹ and these bands are assigned to combination tones. The <i>v</i>_asym.NO₂ mode occurs in the region 1533.60-1538.73 cm⁻¹ and the <i>v</i>_sym.NO₂ mode occurs in the region 1344.07-1345.63 cm⁻¹ for 4-nitrobenzaldehyde in CHCl₃/CCl₄ solutions. The <i>v</i>_sym.NO₂ mode shifts to lower frequency by ∼4.8 cm⁻¹, while the <i>v</i>_sym.NO₂ mode shifts to higher frequency by ∼1.6 cm⁻¹ in going from CCl₄ solution to CHCl₃ solution. The <i>v</i>CN mode for 4-cyanobenzaldehyde increases in frequency in a nonlinear manner as the mole % CHCl₃/CCl₄ increases. The <i>v</i>OH mode for 4-hydroxybenzaldehyde decreases in frequency in essentially a linear manner as the mole % CHCl₃/CCl₄ increases. The δCH mode for 4-<i>x</i>-benzaldehydes increases in frequency as the mole % CHCl₃/CCl₄ increases; however, neither unperturbed <i>v</i>CH nor δCH correlates with Hammett σ_<i>p</i> values.

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