Barrier to internal rotation, symmetry and carbonyl reactivity in methyl 3,3,3-trifluoropyruvate

Abstract

Abstract High-resolution rotational spectroscopy was used to investigate the conformational landscape of methyl-3,3,3-trifluoropyruvate, a small, partially-fluorinated molecule, which is of interest because of its chemical properties and reactivity in contrast to the unfluorinated species. Methyl 3,3,3-trifluoropyruvate is also subject to two possible large amplitude motions of the methyl and trifluoromethyl group. However, only the methyl rotor gives rise to the tunneling splitting specific to individual conformers. In the rotational spectrum measured in the frequency region from 6 to 27 GHz, the identified conformers, s-cis and s-trans, were fitted to experimental accuracy, resulting in the accurate determination of the vibrational ground state rotational constants A 0 = 2185.05827 36 MHz ${A}_{0}=2185.05827\left(36\right)\text{\hspace{0.17em}MHz}$ , B 0 = 1023.300 31 17 MHz ${B}_{0}=1023.30031\left(17\right)\text{\hspace{0.17em}MHz}$ , and C 0 = 803.520287 95 MHz ${C}_{0}=803.520287\left(95\right)\text{\hspace{0.17em}MHz}$ for the s-cis conformer, and A 0 = 2706.9024 ( 49 ) MHz ${A}_{0}=2706.9024\left(49\right)\text{\hspace{0.17em}MHz}$ , B 0 = 864.889 539 ( 81 ) MHz ${B}_{0}=864.889539\left(81\right)\text{\hspace{0.17em}MHz}$ , and C 0 = 746.532 896 ( 71 ) MHz ${C}_{0}=746.532896\left(71\right)\text{\hspace{0.17em}MHz}$ for the s-trans conformer. Additionally the barrier heights of the methyl rotor V 3 CH 3 = 363 . 116 94 cm − 1 ${V}_{3}\left({\text{CH}}_{3}\right)=363.116\left(94\right){\text{\hspace{0.17em}cm}}^{-1}$ and V 3 ( CH 3 ) = 389.290 ( 80 ) cm − 1 ${V}_{3}\left({\text{CH}}_{3}\right)=389.290\left(80\right){\text{\hspace{0.17em}cm}}^{-1}$ were obtained for the s-cis and s-trans conformer, respectively.