The high pressure and temperature oxidation of methyl trans-2-nonenoate, methyl trans-3-nonenoate, 1-octene, and trans-2-octene are investigated experimentally to probe the influence of the double bond position on the chemical kinetics of long esters and alkenes. Single pulse shock tube experiments are performed in the ranges p = 3.8-6.2 MPa and T = 850-1500 K, with an average reaction time of 2 ms. Gas chromatographic measurements indicate increased reactivity for trans-2-octene compared to 1-octene, whereas both methyl nonenoate isomers have reactivities similar to that of 1-octene. A difference in the yield of stable intermediates is observed for the octenes when compared to the methyl nonenoates. Chemical kinetic models are developed with the aid of the Reaction Mechanism Generator to interpret the experimental results. The models are created using two different base chemistry submodels to investigate the influence of the foundational chemistry (i.e., C0-C4), whereas Monte Carlo simulations are performed to examine the quality of agreement with the experimental results. Significant uncertainties are found in the chemistry of unsaturated esters with the double bonds located close to the ester groups. This work highlights the importance of the foundational chemistry in predictive chemical kinetics of biodiesel combustion at engine relevant conditions.