Structures, intramolecular rotation barriers, and thermochemical properties: Ethanol, a-monoethanols, dichloroethanols, and corresponding radicals derived from h atom loss

Document Type

Article

Publication Date

10-18-2001

Abstract

Structures and thermochemical properties on ethanol, two a-chloroethanols; ethoxy and two a-chloroethoxy radicals; a-hydroxyethyl and a-hydroxychloroethyl radical; and/Miydroxyethyl and two /J-hydroxychloroethyl radicals are determined by ab initio and density functional calculations. Molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) density functional level, with single point calculations for the energy at the B3LYP/6-31 l+G(3df,2p), QCISD(T)/6-31G(d,p), and CBSQ//B3LYP/6-31G(d,p) levels. The 5°29s and Cp(T)'s (300 < 77K < 1500) from vibrational, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for the internal rotations are calculated at the B3LYP/6-31G(d,p) level, and hindered rotational contributions to So298 and Cp(T)s are calculated by using direct integration over energy levels of the internal rotational potentials. The ΔHfo298 is determined using several isodesmic reactions, and an evaluation of data at each calculation level results in the ΔHfo298 values: -68.63 ±1.24 and -75.72 ±- 1.31 kcal/mol for CH3CHC1OH and CH3CC12OH, respectively. The ΔHfo298 for CH3CHCIO' and CH3CC12O are -14.79 ±2.90 and -21.85 ±2.82 kcal/mol, respectively. The ΔHfo298 for CH3C'C1OH, C'H2CHC1OH, and C'H2CC12OH are -25.89 ±2.13, -17.51 ± 2.13, and -23.79 ±2.13 kcal/mol, respectively. Bond energies for the RO-H and R-OH bonds in a-chloroethanols are 106 and 97 kcal/mol. Groups for use in Benson type additivity estimations are determined for the carbon bonded to oxygen and chlorine(s). The enthalpy values for the C/C/C1/H/O and C/C/C12/O groups are -20.53 and -27.62 kcal/mol, respectively. Hydrogen bond increment groups for the chloroethoxy, a-hydroxychloroethyl, and β-hydroxychloroethyl radicals are also developed. © 2001 American Chemical Society.

Identifier

0035909742 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp011949q

ISSN

10895639

First Page

9543

Last Page

9552

Issue

41

Volume

105

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