SECTION I: Kinetics of HO₂ Abstraction of H Atoms From Hydrocarbons

Structures, internal rotational barriers and ideal gas thermochemical properties, ΔH^°_f98 for representative series of transition states for abstraction of H atoms from primary, secondary and tertiary hydrocarbons by the HO₂ radical, TC-HOOH (1), TCC-HOOH (2), TC₂C-HOOH (3), TC₃C-HOOH (4), TC₂CC-HOOH (5), TC₂CC-HOOHC (6) and TC₃CCC-HOOH (7) are analyzed in this study. Molecular structures and vibrational frequencies are determined at the B3LYP/6-3111G(d,p) density functional level. The S°₂₉₈ and C_p(T) values (300≤T/K≤1500) from vibrational, translational, and external rotational contributions are calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Internal rotor contributions are included in the S and C_P(T) values. ΔHt°,_TS of the transition states are computed at the G3MP2 level. The forward and reverse rate constants are calculated for the transition state reactions (1) to (7). ΔH_rxn of these paths are estimated. ΔHt°,_TS of species 1, 2, 3, 4 and 5 are also calculated at CBS-Q//B3LYP/6-311G(d,p) level and compared with the G3MP2 results.

SECTION II: Thermochemical Properties, Enthalpy, Entropy and Heat Capacity
(T) for Model Urethane Monomers and Corresponding Radicals.

Two separate model urethanes (carbamates), Ethyl N Ethyl carbamate [C-C-N-C(O)-OC-C] and N (n-propyl) methylcarbamate [C-C-C-N-C(O)-O-C] are utilized to investigate the thermochemical properties and bond energies in several model urethane monomers. Molecular structure, vibration frequencies, energies, enthalpies (ΔH^°_f(298)) and bond energies are determined for the molecules and radicals at the B3LYP/6-31 G(d,p) Density Functional Calculation Level. Entropy (SΔ₍₂₉₈₎) and heat capacity C_P(T) are determined from the above structures and vibration frequencies. Enthalpies of formation (Δ_fH^°_f(298)) are estimated using total energies including zero point vibrational energy (ZPVE), thermal contributions for each species and the calculated ΔH_rxn from isodesmic- working reactions. Bond energies are also calculated. The enthalpy values calculated at the B3LYP/6-31 G(d,p) level for C-C-N-C(O)-O-C-C and C-C-C-N-C(O)-O-C are -115.08 and -113.34 kcal/mol, respectively. Carbon and nitrogen - hydrogen bond energies, calculated in this study are: 453.2 (kJ.mol) for C-C-N_j-C(O)-O-C-C, 400.3 (kJ.mol) for C-C_j-N-C(O)-O-C-C, 430.1 (kJ.mol) for C-C-N-C(O)-O-C-C, 429.4 (kJ.mol) for C-C-NC(O)-O-C_j-C, 439.9 (kJ.mol) for C-C-N-C(O)-O-C-C~, 452.7 (kJ.mol) for C-C-C-NiC(O)-O-C, 401.7 (kJ.mol) for C-C-C_j-N-C(O)-O-C, where j represents the radical site.