TY - JOUR
T1 - 1 H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives
T2 - Barriers to rotation about C{double bond, long}C bond
AU - Marković, R.
AU - Baranac, M.
AU - Juranić, N.
AU - Macura, S.
AU - Cekić, I.
AU - Minić, D.
N1 - Funding Information:
Partial financial support by the Ministry of Science, Technology and Development of the Republic of Serbia, Grant No. 1709 (to R.M.), is acknowledged.
Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.
PY - 2006/12/4
Y1 - 2006/12/4
N2 - The rotational barriers between the configurational isomers of two structurally related push-pull 4-oxothiazolidines, differing in the number of exocyclic C{double bond, long}C bonds, have been determined by dynamic 1 H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl 3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG # 98.5 kJ/mol (at 298 K). The variable-temperature 1 H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d 6 , possessing the two exocyclic C{double bond, long}C bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG # separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the S{single bond}C{double bond, long}C{single bond}C{double bond, long}O entity. The 13 C NMR Δδ C(2)C(2′) values, ranging from 58 to 69 ppm in 1a-d and 49-58 ppm in 2a-d, correlate with the degree of the push-pull character of the exocyclic C(2){double bond, long}C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh ∼ COEt > CONHPh > CONHCH 2 CH 2 Ph. The decrease of the Δδ C(2)C(2′) values in 2a-d has been discussed for the first time in terms of an estimation of the electron donor capacity of the {single bond}S{single bond} fragment on the polarization of the C{double bond, long}C bonds.
AB - The rotational barriers between the configurational isomers of two structurally related push-pull 4-oxothiazolidines, differing in the number of exocyclic C{double bond, long}C bonds, have been determined by dynamic 1 H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl 3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG # 98.5 kJ/mol (at 298 K). The variable-temperature 1 H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d 6 , possessing the two exocyclic C{double bond, long}C bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG # separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the S{single bond}C{double bond, long}C{single bond}C{double bond, long}O entity. The 13 C NMR Δδ C(2)C(2′) values, ranging from 58 to 69 ppm in 1a-d and 49-58 ppm in 2a-d, correlate with the degree of the push-pull character of the exocyclic C(2){double bond, long}C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh ∼ COEt > CONHPh > CONHCH 2 CH 2 Ph. The decrease of the Δδ C(2)C(2′) values in 2a-d has been discussed for the first time in terms of an estimation of the electron donor capacity of the {single bond}S{single bond} fragment on the polarization of the C{double bond, long}C bonds.
KW - 4-Oxothiazolidines
KW - H NMR spectroscopy
KW - Rotational barrier
KW - Z/E-isomerization
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U2 - 10.1016/j.molstruc.2006.03.075
DO - 10.1016/j.molstruc.2006.03.075
M3 - Article
AN - SCOPUS:33750718764
SN - 0022-2860
VL - 800
SP - 85
EP - 92
JO - Journal of Molecular Structure
JF - Journal of Molecular Structure
IS - 1-3
ER -