Wydział Chemii

S. M. Melikova

K. S. Rutkowski

Paweł Rodziewicz

Aleksander Koll

2004

Journal of Molecular Structure

705

49-61

10.1016/j.molstruc.2004.05.022

Naukowa

Angielski

Artykuł

The FTIR spectra of CF₃H and C₂H₂ have been studied in liquefied Ar, N₂, and CO. The frequency blue shift of the C–H stretching vibration accompanied by a decrease in the integrated intensity of the corresponding ν₁ band was found for CF₃H, whereas in the case of C₂H₂ the usual red shift and increasing integrated intensity of the C–H stretching ν₃ band was monitored in the studied series of solvents. Stronger CH⋯BY-type interactions (BY=CD₃CN, (CD₃)₂CO, C₅D₅N, (CD₃)₃N) show first increasing frequency blue shift and then result in the gradual transfer to the usual spectroscopic effect for fluoroform. The self-consistent reaction field approach (SCRF) in the frame of gaussian 98 program could be able to reproduce qualitatively the blue shift and decreasing intensity effects observed on the ν₁ band of CF₃H as well as the conventional red shift and increasing intensity effects only at non-realistically small value of the Onsager radius Å. Ab initio MP2 and density functional theory (DFT)/B3LYP calculations predict weak to medium CH⋯BY complex formation in the case of both CF₃H and C₂H₂ molecules, and suggest the crucial role of the features of the dipole moment function and the intermolecular potential in the observed unconventional effects. The substantial increasing induced dipole moment, accompanied by the predomination of attractive over repulsion forces between H atom of CH group and BY subunit predicted for stronger F₃CH⋯BY interactions result in the transfer from the blue shift and decreasing intensity to conventional spectroscopic effects in accordance with experimental observations.

https://doi.org/10.1016/j.molstruc.2004.05.022

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