Thermochemistry and bond energies of nitro -alkanes, -alkenes, -carbonyls and corresponding nitrites
Document Type
Thesis
Date of Award
Fall 1-31-2009
Degree Name
Master of Science in Environmental Science - (M.S.)
Department
Chemistry and Environmental Science
First Advisor
Joseph W. Bozzelli
Second Advisor
Carol A. Venanzi
Third Advisor
Tamara M. Gund
Abstract
Density functional and ab initio theory based calculations were performed on a series of nitro -alkanes, -alkenes, carbonyl and corresponding nitrites representing large-scale primary, secondary and tertiary nitro compounds and their radicals resulting from the loss of skeletal hydrogen atoms. Geometries, vibration frequencies and thermochemical properties, ΔfH°298, S °(T) and C°p(T) (10K T 5 5000K) are calculated at the individual B3LYP/6-31G(d,p), B3LYP /6-31+G(2d,2p) and composite CBS-QB3 levels. Potential energy barriers for the internal rotations have been computed at the B3LYP/6-31G(d, p) level of theory and the lower barrier contributions are incorporated into entropy and heat capacity data. The standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Recommended values derived from the most stable conformers of respective nitro- and nitrite isomers include: -30.6 and -28.4 kcal moil for n-propane-, -33.9 and -32.3 kcal mol-1 for iso-propane-, -42.8 and -41.4 kcal mol-1 for tert-butane-nitro compounds and nitrites, respectively. Entropy and heat capacity values are also reported for the lower homologues: nitromethane, nitroethane and corresponding nitrites. C--H bond energies are decreased by ~ 5 kcal moil alpha to the nitro or nitrite groups and increased by ~ 0.5 kcal moil beta to the nitro and nitrite groups.
Recommended values for enthalpies of formation of the most stable conformers of nitroacetone, acetonitrite, nitroacetate and acetyl nitrite are -51.6 kcal mol-1, -51.26 kcal mol-1, -45.4 kcal mol-1 and -58.2 kcal mol-1, respectively. The calculated ΔfH°298 for nitroethylene is 7.6 kcal mol-1 and for vinyl nitrite is 7.2 kcal mol-1. The carbonyl and olefin groups retain the major influence on the C-H bond energies. Radicals on carbon adjacent to a nitrite (RC.ONO) group do not exist; they dissociate to the corresponding carbonyl (RC=O + NO) with 38 kcal mol-1 exothermic and no apparent barrier. This results from formation of the strong carbonyl (it bond ~ 80 kcal mol-1) with dissociation of the weak RO--NO bond (-43 kcal mol-1).
Recommended Citation
Snitsiriwat, Surawee, "Thermochemistry and bond energies of nitro -alkanes, -alkenes, -carbonyls and corresponding nitrites" (2009). Theses. 305.
https://digitalcommons.njit.edu/theses/305
