Conformational isomers of trans-urocanic acid observed by rotational spectroscopy. Issue 18 (24th April 2019)

• Record Type: Journal Article
• Authors: Cooper, Graham A.; Medcraft, Chris; Gougoula, Eva; Walker, Nicholas R.
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 18(2019)
• Page Start: 9495
• Page End: 9503
• Publication Date: 2019-04-24
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp00651f
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Rotational spectra have been measured and assigned for four conformers of trans -urocanic acid. Abstract : Rotational spectra have been measured and assigned for four conformers of trans -urocanic acid. The acid was transferred into the gas phase through laser vaporisation of a solid sample, mixed with a neon buffer gas and then cooled through supersonic expansion. Molecules and complexes in the expanding gas jet were probed through chirped-pulse, Fourier transform microwave spectroscopy between 2.0 and 18.5 GHz. Rotational constants, A 0, B 0 and C 0 ; centrifugal distortion constants, Δ J and Δ JK ; and nuclear quadrupole coupling constants of the nitrogen atoms, χ aa (N) and χ bb (N)– χ cc (N), were determined for the various conformers. Data were obtained for ten isotopologues of the conformer that was observed to yield the spectrum of highest intensity. Substitution ( r s ) coordinates were determined for all carbon atoms and two hydrogen atoms of this conformer. Other observed spectra were assigned to conformers on the basis of excellent agreement between calculated and experimentally-determined rotational constants, and empirical observations of the relative intensities of a- and b-type transitions. The results of DFT calculations imply high barriers to the interconversion of assigned conformers.