Structures and thermochemical properties on ethanol, two alpha -chloroethanols; ethoxy and two alpha -chloroethoxy radicals; alpha -hydroxyethyl and alpha -hydroxychloroethyl radical; and beta -hydroxyethyl and two beta -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(o) and C-p(T)'s (300 less than or equal to T/K less than or equal to 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(o) and Cp(T)'s are calculated by using direct integration over energy levels of the internal rotational potentials. The DeltaH(f298)(o) is determined using several isodesmic reactions, and an evaluation of data at each calculation level results in the DeltaH(f298)(o) values: -68.63 +/- 1.24 and -75.72 +/- 1.31 kcal/mol for CH3CHClOH and CH3CCl2OH, respectively. The DeltaH(f298)(o) for CH3CHClO. and CH3CCl2O. are -14.79 +/- 2.90 and -21.85 +/- 2.82 kcal/mol, respectively. The DeltaH(f298)(o) for (CH3CClOH)-Cl-., (CH2CHClOH)-H-., and (CH2CCl2OH)-H-. 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 alpha -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, alpha -hydroxychloroethyl, and beta -hydroxychloroethyl radicals are also developed.