Conformational Landscape, Chirality Recognition and Chiral Analyses: Rotational Spectroscopy of Tetrahydro‐2‐Furoic Acid⋅⋅⋅Propylene Oxide Conformers. Issue 5 (2nd February 2021)

• Record Type: Journal Article
• Authors: Xie, Fan; Seifert, Nathan A.; Hazrah, Arsh S.; Jäger, Wolfgang; Xu, Yunjie
• Is Part Of: Chemphyschem. Volume 22:Issue 5(2021)
• Page Start: 455
• Page End: 460
• Publication Date: 2021-02-02
• Subjects: chirality-controlled structural preference -- chiral-tag spectroscopy -- conformational landscape -- isomerization -- rotational spectroscopy; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202000995
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: A chiral adduct formed between a chiral carboxylic acid, tetrahydro‐2‐furoic acid (THFA), and a chiral ester, propylene oxide (PO), was investigated using rotational spectroscopy and DFT calculations. Isolated THFA exists dominantly as three different conformers: I, II, and III in a jet, with I and II taking on the trans ‐COOH configuration and III having the cis ‐COOH configuration. We utilized CREST, a conformational ensemble space exploration tool, to identify the possible conformations of the binary adduct, THFA⋅⋅⋅PO. Subsequent DFT geometry optimizations predicted about two hundred homochiral and heterochiral binary structures with 28 low energy structures within an energy window of 15 kJ mol −1 . A rich broadband rotational spectrum was obtained with a mixture of trace amounts of THFA+PO in neon in a supersonic jet expansion. Six THFA⋅⋅⋅PO conformers were identified experimentally. Kinetically favored binary products which contain trans ‐COOH I dominate among the observed conformers, while thermodynamically more stable adducts were also detected. Detailed analyses of the structures of the observed conformers show interesting chirality‐controlled structural preferences. Such non‐covalently bound chiral contact pairs are the foundation of chiral‐tag rotational spectroscopy, an exciting new analytical application of rotational spectroscopy for determination of enantiomeric excess. Enantiomeric excess analyses were performed and the results are discussed. Abstract : Chiral preferences ? The complex conformational landscape of a chiral adduct, tetrahydro‐2‐furoic acid⋅⋅⋅propylene oxide, is revealed by rotational spectroscopy and a comprehensive theoretical conformational evaluation strategy. Six binary conformers were identified experimentally and show interesting chirality‐controlled structural preference. Enantiomeric excess experiments were carried out to showcase the power of chiral‐tag rotational spectroscopy.