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Title:CHIRAL TAGGING OF VERBENONE WITH 3-BUTYN-2-OL FOR ESTABLISHING ABSOLUTE CONFIGURATION AND DETERMINING ENANTIOMERIC EXCESS
Author(s):Mayer, Kevin J
Contributor(s):Grubbs II, G. S.; Marshall, Frank E; Sedo, Galen; Pate, Brooks; West, Channing; Smart, Taylor; Holdren, Martin S.; Evangelisti, Luca
Subject(s):Mini-symposium: Chirality-Sensitive Spectroscopy
Abstract:Chiral analysis of a commercial sample of (1S)-(-)-verbenone has been performed using the chiral tag approach. The chirped-pulse Fourier transform microwave spectrum of the verbenone-butynol complex is measured in the 2-8 GHz frequency range. Verbenone is placed in a nozzle reservoir heated to 333K (about 1 Torr vapor pressure). The complex is formed by using a carrier gas of neon with approximately 0.1% butynol. The expansion pressure is about 2 atm. A measurement using racemic butynol is performed to identify isomers of both diastereomer complexes. Quantum chemistry calculations using the B3LYP-D3BJ method with the def2TZVP basis set provided estimated spectroscopic constants for the homochiral and heterochiral complexes. This analysis included 8 isomers for each diastereomer. Four rotational spectra are identified for isomers of the homochiral complex and correspond to the four lowest energy isomers from the theoretical study. Three heterochiral complexes are identified and also correspond to the lowest energy isomers from theory. Subsequent measurements were made with enantiopure tag (both (R)-(+)-3-buty-2-nol and (S)-(-)-3-butyn-2-ol) to establish the absolute configuration of verbenone. The sensitivity of the measurement was sufficient to perform $^{13}$C-isotopologue analysis of three of the homochiral complexes and two of the heterochiral complexes. These results provide definitive structures of verbenone with correct stereochemistry. The commercial sample has relatively low enantiomeric excess with the certificate of analysis reporting an EE of 53.6%. Using the intensities of assigned transitions of the chiral tag complexes, the enantiomeric excess was determined from the broadband rotational spectrum through the ratio of the intensities of pairs of transitions. A total of 2617 pairs of transitions were analyzed. The average EE was found to be 53.6% with a standard deviation of 2%.
Issue Date:6/21/2017
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/97106
DOI:10.15278/isms.2017.WG07
Date Available in IDEALS:2017-07-27


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