Presentation Type

Poster

Keywords

computational chemistry, synthetic chemistry, spectroscopy

Department

Chemistry

Major

Chemistry

Abstract

A series of ketoimines bearing pendant quinolyl substituents were prepared by Schiff base condensation of 1,3-diketones with two different substituents: trifluoromethyl and an alkyl/aryl group (e.g., Me, Et, iPr,tBu, Ph. Synthetic reactions of ketoimines with varying alkyl/aryl substituents altered the distribution of regioisomers as measured in isolated yields and detected by 1H and 19F NMR spectroscopy of crude reaction mixtures. Reaction with the least sterically encumbered diketone (CF3with Me) resulted in mixture of ketoimines with virtually quantitative formation of the ketoimine resulting from quinolyl addition to the carbonyl adjacent to the alkyl substituent. As the steric bulk of the hydrocarbon substituent increased (CF3with Et, iPr, or Ph), a mixture of regioisomers continued, which favored quinolyl addition adjacent to the trifluoromethyl substituent. Only a single ketoimine was isolated or observed with CF3and tBu substituents with quinolyl addition adjacent to CF3. In order to investigate the role of steric and electronic influence of differing alkyl/aryl substitution, Density Functional Theory (DFT) calculation were employed to determine probable transition state structures as well an quantify differences in activation energy between the two regioisomers. Transition state structures were calculated using QST3 calculations verified with IRC calculations at the B3LYP level of theory. Comparisons between DDGdetermined by DFT agreed well with those calculated experimentally and supported steric driven regioselectivity for the series of ketoimines.

Faculty Mentor

Joseph M. Fritsch

Funding Source or Research Program

Summer Undergraduate Research Program

Presentation Session

Session E

Start Date

23-4-2021 3:00 PM

End Date

23-4-2021 3:15 PM

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Apr 23rd, 3:00 PM Apr 23rd, 3:15 PM

Experimental and Theoretical Investigation of Regioselectivity for a Series of Ketoimines with Nuclear Magnetic Resonance Spectroscopy and Density Functional Theory

A series of ketoimines bearing pendant quinolyl substituents were prepared by Schiff base condensation of 1,3-diketones with two different substituents: trifluoromethyl and an alkyl/aryl group (e.g., Me, Et, iPr,tBu, Ph. Synthetic reactions of ketoimines with varying alkyl/aryl substituents altered the distribution of regioisomers as measured in isolated yields and detected by 1H and 19F NMR spectroscopy of crude reaction mixtures. Reaction with the least sterically encumbered diketone (CF3with Me) resulted in mixture of ketoimines with virtually quantitative formation of the ketoimine resulting from quinolyl addition to the carbonyl adjacent to the alkyl substituent. As the steric bulk of the hydrocarbon substituent increased (CF3with Et, iPr, or Ph), a mixture of regioisomers continued, which favored quinolyl addition adjacent to the trifluoromethyl substituent. Only a single ketoimine was isolated or observed with CF3and tBu substituents with quinolyl addition adjacent to CF3. In order to investigate the role of steric and electronic influence of differing alkyl/aryl substitution, Density Functional Theory (DFT) calculation were employed to determine probable transition state structures as well an quantify differences in activation energy between the two regioisomers. Transition state structures were calculated using QST3 calculations verified with IRC calculations at the B3LYP level of theory. Comparisons between DDGdetermined by DFT agreed well with those calculated experimentally and supported steric driven regioselectivity for the series of ketoimines.