Elucidation of fundamental chemical systems through the use of high-level ab initio quantum chemical methods

A goal of any scientist is to gain an understanding for the subject matter at hand. Within quantum chemistry understanding can be achieved through the in-depth study of small systems which retain key features of larger, more chemically interesting species. Within combustion chemistry, the n-propylperoxy radical is the smallest peroxy radical system with an energetically favorable pathway to the formation of the all-important hydroperoxyalkyl radical, a species that is key to low-temperature combustion phenomena. The five rotamers that are formed within the deep potential energy well as the n-propylperoxy radical forms are considered. Focal point analysis and second order vibrational perturbation theory (VPT2) are utilized to differentiate the energies and vibrational frequencies of these nearly isoenergetic species. They hydrogen cyanide dimer represents a small linear system which exhibits hydrogen-bonding phenomena. Results are obtained for this system utilizing a robust combination of method and basis set. The effect of substitution with common isotopes upon vibrational frequencies is investigated using VPT2. Finally, the consideration of simple aluminum (I) compounds, whose valence electron structure mimics that of carbenes are considered. The effect of several substituents, at varying degrees of electrophilicity are investigated. In order to determine the relative energetic favorability, two different schemes, one isodesmic the other hypohomodesmotic are used to determine evaluate the relative energies of formation of different carbene derivatives