VT‐NMR Analysis of Rotation‐Inversion of N ‐(4‐hydroxybutyl)‐ N ‐(2,2,2‐trifluoroethyl) tert ‐butyl Carbamate: Utilizing the −CH 2 CF 3 Appendage as a Reporter on E / Z ‐Isomerization
Year: 2024
Type: article
Abstract: The rotational barrier about the CN carbamate bond of N ‐(4‐hydroxybutyl)‐ N ‐(2,2,2‐trifluoroethyl) tert ‐butyl carbamate 1 was determined by variable temperature (VT) 13 C and 19 F NMR spectroscopy. The −CH 2 CF 3 appendage reports on rotational isomerism and allows for the observation of separate signals for the E ‐ and Z ‐ensembles at low temperature. The activation barrier for E / Z ‐isomerization was quantified using Eyring‐Polanyi theory which requires the measurements of the maximum difference in Larmor frequency Δ ν max and the convergence temperature T c . Both Δ ν max and T c were interpolated by analyzing sigmoidal functions fitted to data describing signal separation and the quality of the superposition of the E ‐ and Z ‐signals, respectively. Methods for generating the quality‐of‐fit parameters for Lorentzian line shape analysis are discussed. Our best experimental value for the rotational barrier Δ G c ≠ ( 1 )=15.65±0.13 kcal/mol is compared to results of a higher level ab initio study of the model N ‐ethyl‐ N ‐(2,2,2‐trifluoroethyl) methyl carbamate.
Source: ChemistrySelect
Authors: Brian Jameson, Rainer Glaser
Institution: Missouri University of Science and Technology
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: bronze
Funder: National Science Foundation
OpenAlex ID: W4395043176