Vinyl and chlorovinyl alcohol species result from the addition of OH radicals to chlorinated olefins under both atmospheric and combustion conditions. Stable vinyl and chlorovinyl alcohols are formed by breaking the C-Cl bonds GO-scission reactions), weaker relative to the newly formed C-OH bonds. Thermochemical properties, DeltaH degrees (f 298), S degrees (298), and C degrees (p)(T) (300 K less than or equal to T less than or equal to 1500 K), are computed by density functional B3LYP/6-31G(d,p) and B3LYP/6-311+G(3df,2p), ab initio QCISD(T)/6-31G(d'), and composite CBS-Q calculation methods for seven chlorovinyl alcohols: CH2=COHCl (1), (E)-CHCl=CHOH (2), (Z)-CHC1=CHOH (3). CCl2=CHOH (4), (E)-CHCl=COHCl (5), (Z)-CHCl=COHCl (6), and CCl2=CClOH (7). Molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) level of theory. Vibration frequencies are scaled for zero-point energies and thermal corrections. Two isodesmic reactions are utilized at each calculation level to determine the DeltaH degrees (f 298) value of each species. Contributions to S degrees (298) and C degrees (298)(T) from translation, vibration, and external rotation are calculated using the rigid-rotor-harmonic-oscillator approximation based on the B3LYP/6-31G(d,p) structures. Hindered internal rotational contributions to entropies and heat capacities are calculated by summation over the energy levels obtained from direct diagonalizations of the Hamiltonian matrix of the internal rotation. The calculated DeltaH degrees (f 298) values show that the syn (s) conformations of 2, 3, 4, 5, and 7 are more stable than their anti (a) forms, which are the same as vinyl alcohol (CH2=CHOH). For 1 and 6, the a forms have lower energies than the s forms due to intramolecular hydrogen bonding between Cl and hydroxyl H. The ideal gas phase DeltaH degrees (f 298) (in kcal/mol) calculated in this study are -38.30 +/- 2.50 for CH2=CClOH (1a), -34.29 +/- 2.75 for (E)-CHCl=CHOH (2s), -38.33 +/- 2.57 for (Z)-CHCl=CHOH (3s), -40.51 +/- 3.02 for CCl2=CHOH (4s), -43.40 +/-. 3.02 for (E)-CHCl=CClOH (5s), -41.15 +/- 3.30 for (Z)CHCl=CClOH (6a), and -44.03 +/- 3.23 for CCl2=CClOH (7s,). The O/C-D/H group (for group additivity) is evaluated from seven syn nonchlorinated simple enols, including vinyl alcohol, 1- and 2-methyl vinyl alcohols, 2,2-dimethyl vinyl alcohol, 1,2,2-trimethyl vinyl alcohol, 2-ethyl vinyl alcohol, and 2-propyl vinyl alcohol and compared with literature data. Standard enthalpies of formation of three new groups-one central-atom C-D/Cl/O group and two interaction groups, HE (for intramolecular hydrogen bonding) and anti (for anti conformers)-are derived as 2.34, -2.28, and 0.98 kcal/mol, respectively. Standard enthalpies of formation of C2HCl3 and C2Cl4 are re-evaluated as -2.86 and -4.53 kcal/mol for use in isodesmic reaction schemes.