Abstract
To study the influence of the position of the double bond and ring size on the stability of hydrogen bonded complexes, the 1:1 complexes formed between 2,2,2-trifluoroethanol (TFE) and three heterocyclic compounds including 2,3-dihydrofuran (2,3-DHF), 2,5-dihydrofuran (2,5-DHF) and 3,4-dihydropyran (3,4-DHP) were investigated systematically. The formation of hydrogen bonded TFE−2,3-DHF, TFE−2,5-DHF and TFE−3,4-DHP complexes were identified by gas phase FTIR spectroscopy at room temperature, and the OH-stretching fundamental transition of TFE was red shifted upon complexation. The competition between the O atom and π-electrons bonding sites within the complexes was studied, and the O−H···π type hydrogen bond was found to be less stable than the O−H···O in all three cases. The observed red shifts of the OH-stretching fundamental transitions in the complexes were attributed to the formation of O−H···O hydrogen bond. Equilibrium constants of the complexation reactions were determined from measured and calculated OH-stretching fundamental intensities. Both theoretical calculations and experimental results reveal that the hydrogen bond strengths in the complexes follow the sequence: TFE−2,5-DHF > TFE−2,3-DHF ≈ TFE−3,4-DHP, thus the position of the double bond exerts significantly larger influence than ring size on the stability of the selected hydrogen bonded complexes.
Highlights
Hydrogen bonding interactions between TFE and various atmospheric components have been explored by many studies, both theoretically and experimentally
The rate coefficients of 2,3-DHF and 3,4-DHP were found to be almost twice higher than that of 2,5-DHF when reacting with the OH radical, and the difference in reactivity was attributed to the conjugation of the double bond with the lone pair of O atom
We investigated the hydrogen bonding interactions between TFE and three heterocyclic compounds (2,3-DHF, 2,5-DHF and 3,4-DHP) systematically
Summary
Hydrogen bonding interactions between TFE and various atmospheric components have been explored by many studies, both theoretically and experimentally. Hydrogen bonded complexes of TFE with ammonia, tetrahydrofuran or diethyl ether in the gas phase studied with Fourier transform infrared (FTIR) spectrometer have been reported, and the formation of these complexes were identified by observed red shifts of the OH-stretching fundamental transitions[9, 15]. FTIR spectroscopy is a primary and helpful technique to study hydrogen bonding interactions[3], because the red shift and intensity enhancement of vibration in X−H upon hydrogen bond formation can be directly obtained from infrared spectra. These parameters are important in identifying and characterizing hydrogen bond[7]. There are three critical goals in this study: (1) to investigate the characteristics of the hydrogen bonded complexes formed between TFE and three heterocyclic compounds; (2) to elucidate the influence of the position of the double bond and ring size on the formation of hydrogen bonded complexes; (3) to study the competition between the O atom and π-electrons bonding sites of the selected heterocyclic molecules in hydrogen bonding interactions
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