Semester

Spring

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Fabien Goulay

Committee Member

Terry Gullion

Committee Member

Michelle Richards-Babb

Committee Member

Stephen Valentine

Committee Member

Alan Bristow

Abstract

Conjugated a, b-unsaturated carbonyl compounds like cyclopentenone play a significant role in various environmental processes. These compounds are formed in combustion and Earth’s atmosphere from the oxidation of cyclic ketones such as cyclopentanone. Once formed under oxidative conditions, cyclopentenone may react with presence of free radicals like OH in the atmosphere molecules to form vinoxy type resonantly stabilized radicals. The presence of free radicals species like OH, O2 in the atmosphere can react with these molecules resulting into intermediate products that dissociate to give final products. Experimental and theoretical investigations in the reactions of cyclopentenone derivatives with these small free radical species are necessary to advance our fundamental understanding of the gas-phase oxidation of conjugated cyclic ketones with a focus on their role toward the formation of resonantly stabilized products. In this project, the reactions of the hydroxyl radical (OH) with cyclopentenone derivatives and cyclopentanone were investigated in a quasi-static reaction cell at 4 Torr over the 300-500 K temperature range. The ketone reactants were introduced in excess and the OH radicals generated using pulsed laser photolysis (PLP) of hydrogen peroxide vapors. The relative concentration of the radical reactant was monitored as a function or reaction time using laser induced fluorescence (LIF). At room temperature, the reaction rate coefficients were measured to be 1.24 ́10-11 cm3 s-1 for reaction with 2-cyclopenten-1-one, 1.71 ́10-11 cm3 s-1 for reaction with 2-metyl-2-cyclopenten- 1-one, 0.44 ́10-11 cm3 s-1, for reaction with 3-metyl-2-cyclopenten-1-one, and 0.29 ́10-11 cm3 s-1 for reaction with cyclopentanone. In the case of 2-cyclopenten-1-one and 2-metyl-2-cyclopenten- 1-one, the values and temperature dependencies of the rate coefficients are like those calculated or measured for non-cyclic conjugated ketones. The rate coefficients for reaction with 3-metyl-2- cyclopenten-1-one is found to behave similarly to the saturated cyclopentanone. Isomeric products are measured for OH radical reactions with cyclopentenone derivatives using photoionization time-of-flight mass spectrometry coupled to synchrotron radiation at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratories in Berkeley, California. Potential energy surfaces calculated at the CBS-QB3 level of theory are used to discuss the experimental data. The relevance for combustion and atmospheric chemistry is discussed.

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