Date of Award
Master of Science in Chemistry - (M.S.)
Chemistry and Environmental Science
Joseph W. Bozzelli
Tamara M. Gund
α,β and α-γ unsaturated carbonyl compounds are important classes of carbonyl compounds with the general structure R-(O=C)-Cα=Cβ-R’ and R-(O=Cγ)-Cβ-Cα=Cβ-R’. These compounds are utilized in industry and are also produced as intermediates of hydrocarbon oxidation in chemistry of the atmosphere and in combustion. These unsaturated carbonyls are common environmental pollutants, are frequently associated with adverse effects, and are considered to play an important role in human cancer. Their stability, thermochemical properties are important to understanding their reaction paths in atmospheric, combustion and bio related environments. Enthalpy, entropy, and heat capacity of unsaturated alkene molecules, and radicals corresponding to hydrogen atom loss from the parent stable molecules are determined in this study. Structures and enthalpies of formation (ΔfHº298) are determined for series of unsaturated carbonyl hydrocarbons and their carbon centered radicals at B3LYP/6-31g(d,p), CBS-QB3 and M062X/6-31+G(d,p) theory levels by using the isodesmic reactions approach. Entropy(S°) and heat capacities (Cp(T)), and the contributions from vibrational, translational and external rotational are calculated using the rigid-rotor-harmonic oscillator approximation, based on the vibration frequencies and structures obtained from density functional studies. Potential barriers for internal rotors in each molecule are determined and used to calculate contributions to So and Cp(T) from the hindered rotors. ΔfHº298 for unsaturated carbonyl alkenes are, CH2=CHCH=O, 16.89 kcal/mol, CH3CH=CHCH2CH=O (trans), 27.41 kcal/mol, CH2=CHCH2CH=O, 19.91 kcal/mol. The trans conformation of CH3CH=CHCH2CH=O is more stable than cis form. For a C-H bond on allylic adjacent to carbonyl group, the allylic has resonance with the carbonyl group. Several bond enthalpies are quite different from that normally found on olefins, and carbonyls. The bond enthalpy for the secondary C-H bonds, adjacent to carbonyl group, are quite low: 77.0 kcal/mol for CC=CC(-H)C=O and 77.8 kcal/mol for C=CC(-H)C=O. The C--H bond enthalpy at the position of secondary vinyl, adjacent to carbonyl group, C=C(-H)C=O shows a value of 113.1 kcal/mol, which is about 5 kcal/mol higher than a normal secondary vinyl C--H bond. The C-H bond enthalpy of the primary vinyl of cdccdo is increased but only by 0.7 kcal/mol from a normal primary.
Jian, Ruiqi, "Thermochemical properties of c3 to c5 unsaturated carbonyl alkenes: enthalpies of formation, entropy, heat capacity, bond enthalpy" (2013). Theses. 186.