Equilibrium Structures and Vibrational Assignments for Isoamyl Alcohol and tert-Amyl Alcohol: A Density Functional Study

Abstract

We have calculated the vibrational spectra of isoamyl alcohol and of tert-amyl alcohol using Density Functional Theory (DFT) with the Becke-3 Lee Yang Parr (B3LYP) functional and a 6-311+G** atomic basis set. The energies of the conformers were also calculated with ab initio Perturbation Theory of second (MP2) and fourth order restricted to single, double and quadruple excitations (MP4 SDQ) with the same basis set. We found rather complicated equilibria of four conformations in each case, counting only those with appreciable abundancies. PED data were compared with GAUSSVIEW animations. The calculated wavenumbers agree rather well with the experimental ones when the gauche-trans conformer is assumed as the most important one for isoamyl alcohol, and the gauchegauche one for tert-amyl alcohol. However, some of the experimental bands had to be assigned also to other conformers, indicating their presence in the equilibrium mixture. Due to sterical reasons both the CO and the OH bonds appear to be weaker in the tertiary alcohol, considering the wavenumbers of the CO and OH bond stretching vibrations. The bond lengths point into the same direction, however, the OH bond in the tertiary alcohol is only slightly longer than that in the primary alcohol.

Intermolecular Hydrogen Bonding in Associated Fluids: The Case of Isopentyl Alcohol Dissolved in Carbon Tetrachloride

“…The first component of these words indicates the position of the C-O bond relative to the neighboring H 2 C-C bond, while the second component indicates the position of the O-H bond relative to the H 2 C-C bond. All structural parameters after optimization and the corresponding harmonic vibrational frequencies are presented in the Supplementary Materials and agree well with the reported results [22]. The differences in enthalpies at 25 • C are listed in Table 1 and displayed schematically in Figure 10 for B3LYP, MP2 and MP4 methods showing the stability order of the conformer structures.…”

“…Figure 11 also shows two different experimental spectra corresponding to concentrations of 0.05 and 0.5 M, with one in the dilute and one in the denser region. The experimental spectrum corresponding to the 0.05 As said, alcohols, like all molecules that easily form hydrogen bonds, are often represented by an infinite equilibrium model that considers associated species such as dimers, trimers and even tetramers [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Thus, to establish a correlation with our experimental findings, the association with isoamyl alcohol was considered.…”

“…Percentages in parentheses indicate the relative populations of conformers in isopentyl alcohol. These values are from reference [22]. Figure 11 presents a direct comparison between the experimental and theoretical IR spectra of the isopentyl alcohol monomer conformers (Figure 11a) and the oligomers and polymers, linear and cyclic species (Figure 11b).…”

Comparative description of the extraordinary phenomenon "thermally activated isobaric partial structure compaction" of water as a solute in some alkanols and alkylamines

“…Therefore, the isobaric heat capacity of TBAlcohol shows a markedly more evident variability with temperature than that observed for unbranched MA [75,76]. The transition from TBAlcohol to TPA entails an increase in steric effects due to the greater number of possible structural conformations in the liquid medium of the latter alkanols (based on the results of calculations using density functional theory) [77] in spite of insignificant differences in their basic thermodynamic properties (see Table 1). Meanwhile, TPA remains liquid up to temperatures below T = 273.15 K. It makes this alcohol a useful alternative to tert-butanol in the study of water solvation effects.…”

Comparative description of the extraordinary phenomenon "thermally activated isobaric partial structure compaction" of water as a solute in some alkanols and alkylamines

“…табл. 1), переход от ТБС к ТПС влечет за собой возрастание стерических эффектов из-за большего числа возможных структурных конформаций в жидкой среде последнего из этих алканолов (по результатам расчетов с привлечением теории функционала плотности) [77]. Между тем, ТПС остается в жидком состоянии до температур ниже T = 273,15 К, что делает этот спирт полезной альтернативой трет-бутанолу в изучении эффектов сольватации воды.…”