Hydrogen bonds play a crucial role in chemistry and biology. Numerous experimental and theoretical studies have been devoted to the elucidation of the structures and the energetics of hydrogen bonds, establishing key features of both intra-molecular and inter-molecular hydrogen bonds by means of different spectroscopic measurements and quantum chemical calculations. In particular, the interaction between acids and water occurs via formation of a hydrogen bond with the acid as the hydrogen donor and the water oxygen as the acceptor. If an electronegative center exists in the acid, another weaker hydrogen bond may be formed with this center as the hydrogen acceptor and the water as the hydrogen donor. Formation of two hydrogen bonds therefore constructs a ring-like structure in the 1:1 acid-water complex. Microwave spectroscopy studies of the dimers of nitric acid [1], sulfuric acid [2], and several carboxylic acids (formic [3], acetic [4], propanonic [5], trifluoroacetic acid [6], trans- and gauche-difluoroacetic [7]) with water have confirmed this structural feature. In many of such spectra, large amplitude motions of the water moiety produce a hyperfine structure of the transition lines. With the aim of getting insight on the behaviour of this kind of dimers, we recorded and assigned the mua- and mub-type rotational spectra of the water complex with both the s-cis and s-trans forms of acrylic acid, the simplest unsaturated carboxylic acid. Besides the parent species, also the spectra of eight isotopomers (COOH-H218O, COOH-D2O, COOD-H2O, COOD-D2O, COOH-DOH, COOH-HOD, COOD-DOH, COOD-HOD) for each conformer were analysed. From the comparison of the rotational constants of all species, precise structural information is obtained. The mub-type transition lines of the parent species and 18O isotopomers are split in two components and a picture of the potential energy surface that leads to this motion has been attempted by quantum-mechanical calculations.
Strong and weak hydrogen bondsin the isolates mono-hydrateds-cis and s-trans acrylic acids
MARIS, ASSIMO;CALABRESE, CAMILLA;CAMINATI, WALTHER;EVANGELISTI, LUCA;FENG, GANG;GOU, QIAN;MELANDRI, SONIA
2013
Abstract
Hydrogen bonds play a crucial role in chemistry and biology. Numerous experimental and theoretical studies have been devoted to the elucidation of the structures and the energetics of hydrogen bonds, establishing key features of both intra-molecular and inter-molecular hydrogen bonds by means of different spectroscopic measurements and quantum chemical calculations. In particular, the interaction between acids and water occurs via formation of a hydrogen bond with the acid as the hydrogen donor and the water oxygen as the acceptor. If an electronegative center exists in the acid, another weaker hydrogen bond may be formed with this center as the hydrogen acceptor and the water as the hydrogen donor. Formation of two hydrogen bonds therefore constructs a ring-like structure in the 1:1 acid-water complex. Microwave spectroscopy studies of the dimers of nitric acid [1], sulfuric acid [2], and several carboxylic acids (formic [3], acetic [4], propanonic [5], trifluoroacetic acid [6], trans- and gauche-difluoroacetic [7]) with water have confirmed this structural feature. In many of such spectra, large amplitude motions of the water moiety produce a hyperfine structure of the transition lines. With the aim of getting insight on the behaviour of this kind of dimers, we recorded and assigned the mua- and mub-type rotational spectra of the water complex with both the s-cis and s-trans forms of acrylic acid, the simplest unsaturated carboxylic acid. Besides the parent species, also the spectra of eight isotopomers (COOH-H218O, COOH-D2O, COOD-H2O, COOD-D2O, COOH-DOH, COOH-HOD, COOD-DOH, COOD-HOD) for each conformer were analysed. From the comparison of the rotational constants of all species, precise structural information is obtained. The mub-type transition lines of the parent species and 18O isotopomers are split in two components and a picture of the potential energy surface that leads to this motion has been attempted by quantum-mechanical calculations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
