Angle of Twist in 4-n alkyl-4′-cyanobiphenyl Molecules (0 ≤ n ≤ 12). Study by Infrared and Raman Spectrometry

Abstract

We report infrared and Raman experiments performed on the nCB series (4-n alkyl-4′-cyanobiphenyl, 0 ≤ n ≤ 12). The thirteen molecules are studied in solution (CC𝓁₄, C₆H₆ or C₆H₁₂) and in crystalline phases, our attention is mainly focused on the value of the angle of twist θ between the aromatic rings. In CC𝓁₄, solutions, measurements of relative integrated Raman intensities in the 1600 cm⁻¹ region indicate a nearly planar conformation in the whole series: θ = 0. Comparison between infrared spectra registered on solutions and on crystals in the range 400–600 cm⁻¹ shows frequency shifts related to θ variations or to changes in the alkyl residue. Analysis of the out of plane bending vibrations located from 461 to 482 cm⁻¹ in the nCB series (B_3a mode in solid biphenyl at 461 cm⁻¹) shows that in solid phase various twisted conformations can be observed: θ value varies from 0 (in OCB) to about 40° (in 3CB or 4CB).

Key Words:

• 4-n alkyl-4′-cyanobiphenyl
• infrared
• Raman