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

Structures and thermochemical properties on ethanol, two α-chloroethanols; ethoxy and two α-chloroethoxy radicals; α-hydroxyethyl and α-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 ° 298 and C p ( T )'s (300 ≤ T /K ≤ 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 ° 298 and C p ( T )'s are calculated by using direct integration over energy levels of the internal rotational potentials. The Δ H f ° 298 is determined using several isodesmic reactions, and an evaluation of data at each calculation level results in the Δ 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 Δ 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 Δ 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 α-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, α-hydroxychloroethyl, and β-hydroxychloroethyl radicals are also developed.