A concerted SCF-MO ab initio and vibrational spectroscopic study of the conformational isomerism in 2-aminoethanol

Abstract

Conformational isomerism in isolated and liquid 2-aminoethanol was investigated by a concerted molecular orbital and vibrational spectroscopic approach. The molecular structures, relative energies, dipole moments and vibrational spectra (both infrared and Raman) of the various possible conformers of the studied compound were calculated, using the extended 6-31G* basis set at the HF-SCF ab initio level of theory. The theoretical results were then used to interpret infrared and Raman data obtained under different experimental conditions. It was found that none of the most populated conformational states existing in the pure liquid (where intermolecular H-bonding occurs extensively)-the gGt and tTt conformers-, correspond to the conformational ground state for the isolated 2-aminoethanol molecule-the intramolecularly H-bonded g H Gg H conformer.

A combined matrix-isolation infrared spectroscopy and MO study of 1-amino-2-propanol

“…As for 2AE and 2AP [3,5], and contrary to what was found for 3AP [4], temperature variation studies carried out on the pure liquid show that there are no detectable amounts of free monomeric molecules in the pure liquid 1AP. The different behavior of 3AP, when compared with the remaining aminoalcohols, has been correlated with the larger conformational exibility in 3AP, which leads to a more favorable OH Á Á Á N intramolecular hydrogen bonding interaction geometry [4,5,27].…”

“…In agreement with the strongest intramolecular OH Á Á Á N hydrogen bond present in the conformational ground state of 3AP, which reduces its tendency to aggregate, the spectroscopic data obtained for this molecule clearly show that monomers assuming this conformation are also present in detectable amounts in the pure liquid [4], while for 2AE and 2AP, where the intramolecular OH Á Á Á N hydrogen bonding is considerably weaker than in 3AP, no experimental evidence could be found for the presence of monomeric species in the pure liquids [3,5].…”

“…The molecules already studied include 2-aminoethanol (2AE) [3], 3-amino-1-propanol (3AP) [4] and 2-amino-1-propanol (2AP) [5], for which we were able to identify the most stable conformers and characterize the most important intramolecular interactions that are responsible for their relative stability. It could be well established that, for the isolated molecules, OH Á Á Á N and NH Á Á Á O intramolecular hydrogen bonding may occur, the former being considerably stronger than the latter and being present in the most stable conformers of all molecules studied [3±5].…”

Thermal study of simple amino-alcohol solutions

“…When comparing the glass-forming tendency of the two compounds, we can see from 40% to 45% (w/w) that 21AE is more effective than 31AP. This observation is backed up by quantum chemical calculations and matrix-isolation infrared experiments conducted on these compounds [12,31], which showed that the intramolecular hydrogen bonding of 31AP is stronger than in 21AE. A significant amount of intramolecularly bond monomers of 31AP was found for this compound in the pure liquid [12], clearly indicating that for this molecule intramolecular hydrogen bonding is of similar strength as intermolecular interactions.…”

“…A significant amount of intramolecularly bond monomers of 31AP was found for this compound in the pure liquid [12], clearly indicating that for this molecule intramolecular hydrogen bonding is of similar strength as intermolecular interactions. As a result, 31AP is less able to create the hydrogen bonds with the water molecules required to disturb and inhibit ice nucleation than 21AE, where no evidence of the presence of intramolecularly bond monomers species was found in the liquid phase [31].…”