Thermochemical Properties (Δ_fH°(298 K), S°(298 K), C_p(T)) and Bond Dissociation Energies for C1–C4 Normal Hydroperoxides and Peroxy Radicals

Abstract

Structure and thermochemical properties of the normal hydroperoxides, C n H2n+1OOH (1 ≤ n ≤ 4), and corresponding peroxy radicals, C n H2n+1OO·(1 ≤ n ≤ 4), are determined by density functional M06-2X, multilevel G4, composite CBS-QB3, and CBS-APNO level calculations. Unique to this study is that the Δf H°298 values are determined using several isodesmic reactions which utilize experimental standard enthalpy data for CH3OOCH3 and CH3CH2OOCH2CH3 as reference species, where previous studies used atomization or work reactions with alcohols or other nonperoxide species. The S°298 and Cp (T) (300 ≤ T/K ≤ 1500) from vibration, translation, and external rotation contributions are calculated based on the vibration frequencies and structures obtained from the density functional study. Potential barriers for the internal rotations are calculated at B3LYP/6-31+G­(d,p) level, the hindered internal rotation contributions to S°298 and Cp (T) are calculated using direct integration over energy levels of the internal rotational potentials. The results show the following Δf H°298 values (units in kcal mol–1): CH3OOH (−31.0), CH3CH2OOH (−39.0), CH3CH2CH2OOH (−44.0), CH3CH2CH2CH2OOH (−48.9),CH3OO· (2.4), CH3CH2OO· (−6.2), CH3CH2CH2OO· (−11.4), and CH3CH2CH2CH2OO· (−16.6). Bond dissociation energies for the R–OOH, RO–OH, ROO–H, R–OOj, and RO–Oj bonds are reported. The enthalpy values from the use of experimental data as a reference show very good agreement and support the data obtained from calculation methods. They should be used for reference values. Entropy and heat capacity values show good agreement with the calculation literature. The standard entropies for butyl hydroperoxide, propyl peroxy, and butyl peroxy are corrected.

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH, and radicals

“…The deviations of our calculated ΔH f o 298 , S o 298 and heat capacity values using the HBI method from those of DFT calculation are within 1.0 kcal mol −1 and 1.0 cal mol −1 K −1 , respectively. Our ΔH f o 298 and S o 298 and C p (K) values for CH 3 SCH•CH 3 are close to those obtained by Vandeputte et al The HBI method for S o (298) and Cp(T) allows calculation of the thermochemical properties of radicals with addition of 1 group to the groups used to estimate the respective properties of the parent molecules …”

“…Uncertainties are calculated based on the CBS‐QB3 level calculation results of the targeted species, and the uncertainties of the reference species in the work reactions …”

“…The uncertainty of a target molecule enthalpy depends on the uncertainty of work reaction calculation method, the uncertainty of reference species, and the number of isodesmic reactions . The calculation of uncertainty has been described in several previous studies . The calculated uncertainties listed in Table 2 are based on the CBS‐QB3 level calculation results of the targeted species, and the uncertainties of the reference species.…”

“…The hydrogen‐bond increment (HBI) method is used for estimation of the thermochemical properties of radicals formed by removal of 1 H atom from the parent molecules . The hydrogen atom bond increment method developed by Lay et al has been illustrated in previous studies .…”

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH, and radicals corresponding to loss of H atom

“…The uncertainty of targeted molecule depends on the uncertainty of work reaction calculation method, the uncertainty of reference species, and the number of isodesmic reactions . The calculation of uncertainty has been described in several previous studies . The uncertainty from isodesmic reactions for each species along with the calculation process is listed in Table S3.…”