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Reports: UR653451-UR6: The Characterization and Conformational Preferences of Long Alkyl Chains Using Advanced Broadband Microwave Spectroscopy

Stephen A. Cooke, PhD, State University of New York, College at Purchase

The proposed, ongoing work consists of three goals all of which involve the use of microwave spectroscopy to study molecules of petrochemical interest. The first goal is to characterize end group effects on the conformations of long alkyl chains, the second goal is the fingerprinting of oligomeric tacticity, and the third goal being to study the potential energy surfaces of long alkyl chain methyl ethers. In our first year of support we have focused our efforts on the methyl ether project.

Briefly, ethyl methyl ether exists in a trans conformer in its lowest energy configuration. The next member of the series, propyl methyl ether, has, curiously, only been studied as the trans-trans conformer, with the aim of that study being to compare geometric parameters to ethyl methyl ether. This is curious because the lowest energy conformer of propyl methyl ether is the trans-gauche configuration, i.e. the O-C-C-C dihedral is approximately 60o. Butyl methyl ether, and the higher members have not been the subject of any prior microwave spectroscopic studies. We proposed to study these molecules using microwave spectroscopy with the goal of establishing the conformations of the alkyl chain.

We have successfully recorded the pure rotational spectrum of butyl methyl ether. Furthermore, we have synthesized the pentyl methyl ether and recorded its rotational spectrum. The synthesis of hexyl methyl ether is complete, and its microwave spectrum is next to be recorded. Through the analysis of the rotational spectrum for butyl methyl ether, performed by our students, we have located the lowest energy conformer also contains the O-C-C-C dihedral angle of approximately 60 degrees. The analysis of the pentyl methyl ether is ongoing, as is the analysis of the observable effects of the methoxy internal rotation in these molecules.

We have also recorded the rotational spectra of several molecules containing long alkyl chains. This novel work is ongoing but one outcome has already been published.

In regards to impact upon the personnel’s careers all four undergraduates who have been supported by this award are making applications to graduate school to pursue advanced degrees in the field of chemistry or medicine. All data obtained will be publishable in a peer reviewed journal such as the Journal of Molecular Spectroscopy or Journal of Molecular Structure.