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  • 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
Title: 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
Abstract The rotational barrier about the CN carbamate bond ofN‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl)tert‐butyl carbamate1was determined by variable temperature (VT)13C and19F 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 modelN‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate.  more » « less
Award ID(s):
2153206
PAR ID:
10510926
Author(s) / Creator(s):
;
Publisher / Repository:
Chemistry Europe
Date Published:
Journal Name:
ChemistrySelect
Volume:
9
Issue:
16
ISSN:
2365-6549
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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