Mendeleev Commun., 2019, 29, 495–497
All the studied trans-(RS)-cyclohexanols 2a–c prefer to exist
performed by the majority of structurally similar trans-2-
aminocyclohexanols studied previously.6,7 The obvious
dependence of the sensitivity to acid on the structure of N-hetaryl
group motivates for further studies of these promising models.
in the diequatorial conformation 2B in all solvents (70–100%,
see Table 1). This preference is substantially smaller than could
be expected from the data for similar models with R = Me, Ph
that were found to be completely diequatorial regardless of
solvent and temperature.8 Interestingly, the preference for the
apparently more polar form 2B is stronger in relatively non-polar
CDCl3 than in polar solvents. A plausible explanation for this
difference may be an intramolecular hydrogen bond OH···N in
the current N-hetaryl derivatives, which stabilizes 2B in CDCl3,
but is interrupted by interaction with CD3OD and especially with
(CD3)2SO.
The conformational equilibrium of the molecules 1 in polar
solvents is strongly shifted towards conformation 1A, where two
ethoxycarbonyl counterbalances are in equatorial positions.
However, the opposite conformation 1B is almost equally
populated or even slightly predominant in non-polar CDCl3,
apparently because of the stabilizing intramolecular hydrogen
bond (see above). Previously we estimated the destabilizing
effect of two axial COOEt groups in structures similar to 1B
(with R = alkyl) as 7 to 8 kJ mol–1 in C6D12 and approximately
10 kJ mol–1 in CDCl3 and (CD3)2CO.9 A comparison of the
DGB–A data in Tables 1 and 2 (1 vs. 2) gives similar values:
7.3–8.6 kJ mol–1 in CDCl3, 12–14 kJ mol–1 in (CD3)2SO, and
10–13 kJ mol–1 in CD3OD.
This work was made possible by the NSF Instrumentation
Grant NSF-MRI-0722654 (funding of the JEOL ECA-600 NMR
spectrometer). The Stauffer Grant from the Department of
Chemistry, University of the Pacific (UOP), the Pacific Fund
Grant from UOP, the Dean’s Undergraduate Research Award
from UOP, and the support from the Department of Chemistry at
UOP are gratefully acknowledged. The authors also thank
Professor O. David Sparkman, Dr. Patrick Batoon and Dr.
Michael Pastor for the use of the Pacific Mass Spectrometry
Facility.
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.09.005.
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Received: 6th May 2019; Com. 19/5912
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