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

Structure and thermochemical properties of the normal hydroperoxides, C n H 2 n +1 OOH (1 ≤ n ≤ 4), and corresponding peroxy radicals, C n H 2 n +1 OO·(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 Δ f H ° 298 values are determined using several isodesmic reactions which utilize experimental standard enthalpy data for CH 3 OOCH 3 and CH 3 CH 2 OOCH 2 CH 3 as reference species, where previous studies used atomization or work reactions with alcohols or other nonperoxide species. The S ° 298 and C p ( 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 C p ( T ) are calculated using direct integration over energy levels of the internal rotational potentials. The results show the following Δ f H ° 298 values (units in kcal mol –1 ): CH 3 OOH (−31.0), CH 3 CH 2 OOH (−39.0), CH 3 CH 2 CH 2 OOH (−44.0), CH 3 CH 2 CH 2 CH 2 OOH (−48.9),CH 3 OO· (2.4), CH 3 CH 2 OO· (−6.2), CH 3 CH 2 CH 2 OO· (−11.4), and CH 3 CH 2 CH 2 CH 2 OO· (−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.