Structures, rotational barriers, and thermodynamic properties of C2 vinyl and chlorovinyl alcohols and additivity groups

Document Type

Article

Publication Date

10-12-2000

Abstract

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 (β-scission reactions), weaker relative to the newly formed C-OH bonds. Thermochemical properties, Δf298°, S298°, and Cp°(T) (300 K ≤ T ≤ 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=COHC1 (1), (£)-CHCl=CHOH (2), (Z)-CHC1=CHOH (3), CCl2=CHOH (4), (E)-CHC1=COHC1 (5), (Z)-CHCl=COHC1 (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 ΔHf298° value of each species. Contributions to S298° Cp°(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 ΔHf298° 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 ΔHf298° (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)-CHC1=CClOH (5s), -41.15 ± 3.40 for (Z)-CHCl=CClOH (6a), and -44.03 ± 3.23 for CCl2=CClOH (7s,). The O/CD/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 CD/Cl/O group and two interaction groups, HB (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. © 2000 American Chemical Society.

Identifier

0011136282 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp001531c

ISSN

10895639

First Page

9197

Last Page

9206

Issue

40

Volume

104

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