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) 13C and 19F NMR spectroscopy. The −CH2CF3 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 Δνmax and the convergence temperature Tc. Both Δνmax and Tc 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 ΔGc≠(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.
Recommended Citation
B. Jameson and R. Glaser, "VT-NMR Analysis Of Rotation-Inversion Of N-(4-hydroxybutyl)-N-(2,2,2-trifluoroethyl) Tert-butyl Carbamate: Utilizing The −CH2CF3 Appendage As A Reporter On E/Z-Isomerization," ChemistrySelect, vol. 9, no. 16, article no. e202401323, Wiley, Apr 2024.
The definitive version is available at https://doi.org/10.1002/slct.202401323
Department(s)
Chemistry
Publication Status
Full Access
Keywords and Phrases
E/Z-Isomerization; Eyring-Polanyi Equation; Fluorinated Carbamates; Lorentzian Line Fitting; Variable Temperature NMR Spectroscopy
International Standard Serial Number (ISSN)
2365-6549
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2024 Wiley, All rights reserved.
Publication Date
24 Apr 2024
Comments
National Science Foundation, Grant 1665487