IR Spectra of Hydrogen-Bonded Complexes of Trifluoroacetic Acid with Acetone and Diethyl Ether in the Gas Phase. Interaction between CH and OH Stretching Vibrations

The spectra of complexes of trifluoroacetic acid (TFA) with acetone and diethyl ether (DEE) and their perdeuterated isotopologues were extracted from the spectra of the mixture of the compounds recorded at room temperature. The is nu(OH) bands of the complexes with protiated and deuterated acetone notably differ from each other, whereas these nu(OH) bands are practically not affected by the deuteration of DEE. An assumption about the interaction of CH and OH groups in the (CH3)-C=O center dot center dot center dot HO fragment is made. According to density functional theory calculations, complexes of TFA with both acetone and DEE have a cyclic structure with one strong =O center dot center dot center dot HO hydrogen bond and one weak CH center dot center dot center dot O= bond. The structural, spectroscopic, and electronic properties indicate an essential role of weak bonds in the total complexation energy of the systems studied.