Chiral tagging of verbenone with 3-butyn-2-ol for establishing absolute configuration and determining enantiomeric excess

Mayer, Kevin J.

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https://hdl.handle.net/2142/97106 Copy

Description

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, G.S., II
• Marshall, Frank E.
• Sedo, Galen
• Pate, Brooks
• West, Channing
• Smart, Taylor
• Holdren, Martin S.
• Evangelisti, Luca

Issue Date

2017-06-21

Keyword(s)

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%.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/97106

DOI

https://doi.org/10.15278/isms.2017.WG07

Copyright and License Information

Copyright 2017 Kevin J. Mayer

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