Thermochemical Properties, Rotation Barriers, Bond Energies, and Group Additivity for Vinyl, Phenyl, Ethynyl, and Allyl Peroxides

Abstract

Peroxides have relatively low stability and are often difficult to obtain at needed purity for experimental studies. This study uses computational chemistry to estimate thermochemical properties of peroxides and compares the values to properties of corresponding hydroperoxides. The combined thermochemical properties are utilized to develop groups for use in group additivity. Structures, enthalpy (∆ f H°2 98 ), entropy (S°2 98 ), and heat capacity (C p (T)) are determined for several vinyl, allyl, ethynyl, and phenyl peroxides using the density functional B3LYP/6-311G(d,p) calculations. Enthalpies of formation (∆ f H°2 98 ) are determined at the B3LYP/ 6-311G(d,p) level using four to six isodesmic working reactions. Entropy (S) and heat capacity (C p (T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonicoscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contribution to ∆ f H(T), S, and C p (T) from analysis on the internal rotors is included. ∆ f H°2 98 for vinyl-methyl peroxide, CH 2 dCHOOCH 3 , is -10.04 ( 0.66 kcal mol -1 and for allyl-methyl peroxide, CH 2 dCHCH 2 OOCH 3 , is -12.08 ( 1.05 kcal mol -1 . Methyl-substituted vinyl peroxide values are CH 2 d C(CH 3 )OOCH 3 ) -20.79 ( 0.42, CH 3 CHdC(CH 3 )OOCH 3 ) -29.58 ( 0.32, and CH 3 (CH 3 )CdCHOOCH 3 ) -30.60 ( 0.90 kcal mol -1 . The cis conformation of CH 3 CHdCHOOCH 3 , -21.27 ( 0.47 kcal mol -1 , is more stable than the trans form, -19.95 ( 0.67 kcal mol -1 . Enthalpies for ethynyl peroxides are 41.31 ( 0.72 kcal mol -1 for HCtCOOCH 3 and 29.51 ( 0.27 kcal mol -1 for CH 3 CtCOOCH 3 . The calculated ∆ f H°2 98 for phenyl peroxide, C 6 H 5 OOCH 3 , is -2.19 ( 0.52 kcal mol -1 . The resulting peroxide enthalpies allow determination of the RO-OC, ROO-C bond energies. The vinyl, phenyl and ethynyl peroxides are unstable and rapidly dissociate via cleaving of the weak RO-OR′ peroxide bond with formation of a strong carbonyl bond. Enthalpy of formation was also calculated for CH 3 OOCH 3 (-30.77 ( 0.64 kcal mol -1 ) and CH 3 CH 2 -OOCH 3 (-39.0 ( 0.24 kcal mol -1 ) due to the need for these enthalpy values in the working reaction analysis. Thermodynamic properties for the oxygenated carbon groups O/C d /O, O/C b /O, C t /O, O/C t /O, and O/C/C t were also determined. The agreement between group additivity and calculated enthalpies and heat capacities for the different classes of molecules studied supports the group additivity principal for these systems.

Enthalpy of formation and bond energies on unsaturated oxygenated hydrocarbons using G3MP2B3 calculation methods

“…The standard deviation between B3LYP/6-31G(d,p) and CBS-Q//B3LYP/6-31G(d,p) on six species varies from ±0.7 to ±1.6 kcal mol −1 and the standard deviation is ±0.38 to ±1.76 kcal mol −1 between B3LYP/6-311++G(3df,2p) and CBS-Q//B3LYP/6-31G(d,p [12] with DFT and −39.52 [19] by CBSq//MP2 (full)/6-31G(d). Enthalpy calculations for radicals have also shown agreement: CH 3 OO· is 2.07 ± 0.7 [20] at CBS/APNO, 2.24 [21] at G2, while DFT results in 2.02 ± 0.1 [17]; CH 3 CH 2 OO· is −6.7 [22], −6.8 [22], −6.8 ± 0.7 [20] at CBS-Q//B3LYP/6-31G(d,p), G2, and CBS/APNO respectively, while DFT is at −5.75 ± 0.1 [17]. CH 2 · CH 2 OOH is 11.2 [22] at CBS-Q//B3LYP/6-31G(d,p) and 11.34 ± 1 [17] with DFT; CH 2 CHOO· is reported as 24.45 by G2M(RCC,MP2) [23] and 24.34 ± 0.42 [17] by DFT.…”

Thermochemical Properties and Group Values for Nitrogen-Containing Molecules

“…10,11,15 As is customary when deriving group values, the entropy used in the fitting procedure was the so-called intrinsic entropy, which ignores external and rotor symmetry and treats each atom in the molecule as distinguishable. 8 The intrinsic entropy is computed by adding Rln(σ) to the molecular entropy.…”

Prediction of Thermodynamic and Kinetic Parameters for Interfacial Reactions of the SIO2System by Quantum Chemistry Methods

“…The four basis set calculations result in remarkably good agreement. Comparison of results from smaller basis sets 67 CBS-APNO −30.9 ± 0.7 61 CBS-APNO −33 68 MM and ab initio calculation −31.3 69 Heat of equilibrium measurement −30.75 70 CBS-Q Own value 57 −31.72 ± 1.02 B3LYP/6-311G(d,p) 61 Derived from experiment −40 73 MM and ab initio calculation −38.78 70 CBS-Q Own value 59 −39.28 ± 0.01 B3LYP/6-311G(d,p) 77 Experiment CH 3 + O 2 ←→ CH 3 OO 2.07 ± 0.7 61 CBS/APNO Own value 57 2.02 77 Experiment CH 3 CH 2 + O 2 ←→ CH 3 CH 2 OO −6.8 ± 0.7 61 CBS/APNO −6.8 ± 2.3 61 Negative-ion/acidity/CBS Own value 57 −5.75 ± 0.1 B3LYP/6-311G(d,p) CH 2 •CH 2 OOH 11.12 60 CBS-q//MP2 (full)/6-31G(d) 10.85 60 MP2//MP2 (full)/6-31G(d) 10.5 67 G2 Own value 57 10. 93 with the reference one allows an estimation of the deviation and is a measure of the relative error in the method.…”