Structures, Intramolecular Rotation Barriers, and Thermochemical Properties:  Ethanol, α-Monoethanols, Dichloroethanols, and Corresponding Radicals Derived from H Atom Loss

Abstract

Structures and thermochemical properties on ethanol, two R-chloroethanols; ethoxy and two R-chloroethoxy radicals; R-hydroxyethyl and R-hydroxychloroethyl radical; and β-hydroxyethyl and two β-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/6-311+G(3df,2p), QCISD(T)/6-31G(d,p), and CBSQ//B3LYP/6-31G(d,p) levels. The S°2 98 and C p (T)'s (300 e T/K e 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 S°2 98 and C p (T)'s are calculated by using direct integration over energy levels of the internal rotational potentials. The ∆H f °298 is determined using several isodesmic reactions, and an evaluation of data at each calculation level results in the ∆H f °298 values: -68. 63 ( 1.24 and -75.72 ( 1.31 kcal/mol for CH 3 CHClOH and CH 3 CCl 2 OH, respectively. The ∆H f °298 for CH 3 CHClO • and CH 3 CCl 2 O • are -14.79 ( 2.90 and -21.85 ( 2.82 kcal/mol, respectively. The ∆H f °298 for CH 3 C • ClOH, C • H 2 CHClOH, and C • H 2 CCl 2 OH 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 R-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/Cl/H/O and C/C/Cl 2 /O groups are -20.53 and -27.62 kcal/mol, respectively. Hydrogen bond increment groups for the chloroethoxy, R-hydroxychloroethyl, and β-hydroxychloroethyl radicals are also developed.

Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociations

“…The method of isodesmic reactions is used to determine the enthalpy of formation (ΔH f ° 298 ) for C·H 2 CHO and CH 3 C·O radical species. It provides higher accuracy for estimates of ΔH f ° 298 than heats of atomization does 27–31.…”

The asymmetric top–asymmetric frame internal rotation spectrum of ethyl alcohol

“…The conformational effects on the infrared spectrum have been the subject of many investigations including a series of experimental and theoretical investigations into the OH overtones [36][37][38][39][40][41][42][43][44][45] and a series of experimental and theoretical investigations into the rotational isomerism and conformational effects on the infrared spectrum [46][47][48][49][50][51][52][53][54][55]. More recent work has focused on understanding the conformational ordering of clusters and the implications to the isomerism observed in solids [56][57][58][59][60][61][62][63][64].…”

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH, and radicals corresponding to loss of H atom

“…S° 298 was calculated on the basis of the following: where the gas constant R equals to 1.987 cal mol ‐1 K ‐1 , and σ and OI stand for the number of symmetry and optical isomer of the targeted molecule, respectively. The thermochemical properties of these groups were taken from the existing literature …”

“…Change in the symmetry number of the radical compared to the molecule needs to be considered when calculating 298 K entropy (S° 298 ) for the radical. The radical's entropy value in Tables and was calculated on the basis of the following: where the gas constant R is equal to 1.987 cal mol ‐1 K ‐1 , σ stands for the symmetry numbers of CH 2 •SCH 2 CH 2 OH (2) and CH 3 SCH 2 CH 2 OH (3), and OI stands for the numbers of optical isomers of CH 2 •SCH 2 CH 2 OH (1) and CH 3 SCH 2 CH 2 OH (1).…”