This PhD thesis describes the gas phase studies of four intramolecular hydrogen bonds: O-H···O (in methyl lactate), O-H···π (in methallyl carbinol and allyl carbinol), O-H···N (in methylated and triuoromethylated 2-aminoethanol) and N-H···N (in the diamines 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane).
Experimentally, the hydrogen bonds have been studied with vibrational spectroscopy in the infrared and near-infrared regions. The focus is primarily on spectra recorded in the near-infrared regions, which in these studies are dominated by O-H and N-H stretching overtones. Overtone spectra have been recorded with intracavity laser photoacoustic laser spectroscopy and conventional long path absorption spectroscopy.
Theoretically, a combination of electronic structure calculations and local mode models have been employed to guide the assignment of bands in the vibrational spectra. The experimental characterization of hydrogen bonds have been complemented by theoretical analyzes. These analyzes are based on the electron density topology, natural bond orbital theory and visualization of the distribution of electrostatic potential energy in the molecules.
In these studies, weak intramolecular hydrogen bonds in methyl lactate, allyl carbinol and methallyl carbinol have been identified and characterized. The effect of substitution of two hydrogen atoms on one of the methylene groups with either methyl groups or tri
uoromethyl groups on the intramolecular O-H···N hydrogen bond in 2-aminoethanol was investigated. Whereas the effect of methyl group substitution was limited, the
effect of triuoromethyl group substitution was shown to strengthen the intramolecular hydrogen bond in 2-aminoethanol signicantly. For the diamines 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane, no sign of intramolecular N-H···N hydrogen bonds were identified in the overtone spectra. However, theoretical analyzes indicate that intramolecular N-H···N hydrogen bonds are present in all three diamines if two hydrogen atoms on one of the methylene groups are substituted with triuoromethyl
groups.