On the blue-shifting hydrogen bond in tribromoacetaldehyde dimers

The dimerisation of tribromoacetaldehyde in CCl4 and C6D12 solutions was investigated using Raman spectroscopy and different techniques of multivariate analysis. The ν(C–H) stretching vibration band in dimers was blue shifted by 14/15 cm−1, whereas the ν(CO) dimer band was red-shifted by 7/8 cm−1 in CCl4/C6D12 solutions versus their positions in monomers. The observed shifts were accompanied by a strong change in the bandwidth. The formation of dimers was confirmed by multivariate analysis of the Raman spectra of bromal recorded as a function of temperature. Structural and spectral information for (Br3CCHO)2 dimers were obtained from calculations at the B3LYP/6-311++G(3df,3pd) level.