Elucidating the Thermochemistry and Rate Kinetics of 2‑Ethylhexyl Nitrate: An H Atom Abstraction Reactions Approach

2-Ethylhexyl nitrate (EHN) is a promising high energy
liquid fuel
candidate due to its high reactivity and rapid energy release. Understanding
the multichannel H atom abstraction mechanisms in EHN combustion is
essential for improving combustion modeling accuracy. This study employs ab initio methods and transition state theory (TST) to systematically
investigate H-abstraction reactions at four specific sites in EHN,
initiated by six abstractors: Ḣ, ȮH, HȮ2, ṄO2, O2, and ĊN. Geometry optimizations,
frequency analyses, and dihedral scans were performed using the M06-2X/6-311++G
(d, p) method. Torsional modes were treated by using a one-dimensional
hindered rotor approximation. Single-point energies (SPEs) were calculated
via QCISD/cc-pVXZ (X = T, Q) and MP2/cc-pVYZ (Y = D, T, and Q) with
complete basis set (CBS) extrapolation. High-pressure limit rate constants
of all of the reaction channels were calculated at a wide temperature
range from 298.15 to 2000 K by taking asymmetric Eckart tunneling
corrections into account. In addition, the bond dissociation energies
(BDEs) of seven bonds in EHN were determined, and thermochemical properties
of relevant species were calculated via the atomization method. Finally,
the effect of different functional groups on the reactivity of H abstraction
was explored. Key findings include: (1) an O–N bond, with the
lowest BDE at 42.83 kcal mol–1, demonstrating that
it is the most susceptible to bond fission; (2) C2 is the
most reactive site for H-abstraction; (3) ĊN and ȮH
are particularly competitive abstractors; and (4) nitrogen-containing
functional groups have a very slight effect on the H abstraction reaction
as compared to non-nitrogen-containing functional groups.