H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond
Abstract
The rotational barriers between the configurational isomers of two structurally related push-pull 4-oxothiazolidines, differing in the number of exocyclic C=C bonds, have been determined by dynamic H-1 NMR spectroscopy. The equilibrium mixture of (5-ethoxy-carbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier Delta G(#) 98.5 kJ/mol (at 298 K). The variable-temperature H-1 NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d(6), possessing the two exocyclic C=C bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier Delta G(#) 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 ( gt 90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type (SO)-O-... in...teractions within the S-C=C-C=O entity. The C-13 NMR Delta delta(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)=C(2') bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2') position in the following order: COPh similar to COEt gt CONHPh gt CONHCH2CH2Ph. The decrease of the Delta delta(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 -S- fragment on the polarization of the C=C bonds. (c) 2006 Elsevier B.V. All rights reserved.
Keywords:
4-oxothiazolidines / Z/E-isomerization / rotational barrier / H-1 NMR spectroscopySource:
Journal of Molecular Structure, 2006, 800, 1-3, 85-92Publisher:
- Elsevier Science Bv, Amsterdam
DOI: 10.1016/j.molstruc.2006.03.075
ISSN: 0022-2860
WoS: 000242743600011
Scopus: 2-s2.0-33750718764
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Hemijski fakultet / Faculty of ChemistryTY - JOUR AU - Marković, R. AU - Baranac-Stojanović, Marija AU - Juranić, N. AU - Macura, S. AU - Cekic, I. AU - Minić, Dragica M. PY - 2006 UR - https://cherry.chem.bg.ac.rs/handle/123456789/813 AB - The rotational barriers between the configurational isomers of two structurally related push-pull 4-oxothiazolidines, differing in the number of exocyclic C=C bonds, have been determined by dynamic H-1 NMR spectroscopy. The equilibrium mixture of (5-ethoxy-carbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier Delta G(#) 98.5 kJ/mol (at 298 K). The variable-temperature H-1 NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d(6), possessing the two exocyclic C=C bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier Delta G(#) 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 ( gt 90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type (SO)-O-... interactions within the S-C=C-C=O entity. The C-13 NMR Delta delta(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)=C(2') bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2') position in the following order: COPh similar to COEt gt CONHPh gt CONHCH2CH2Ph. The decrease of the Delta delta(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 -S- fragment on the polarization of the C=C bonds. (c) 2006 Elsevier B.V. All rights reserved. PB - Elsevier Science Bv, Amsterdam T2 - Journal of Molecular Structure T1 - H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond VL - 800 IS - 1-3 SP - 85 EP - 92 DO - 10.1016/j.molstruc.2006.03.075 ER -
@article{ author = "Marković, R. and Baranac-Stojanović, Marija and Juranić, N. and Macura, S. and Cekic, I. and Minić, Dragica M.", year = "2006", abstract = "The rotational barriers between the configurational isomers of two structurally related push-pull 4-oxothiazolidines, differing in the number of exocyclic C=C bonds, have been determined by dynamic H-1 NMR spectroscopy. The equilibrium mixture of (5-ethoxy-carbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier Delta G(#) 98.5 kJ/mol (at 298 K). The variable-temperature H-1 NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d(6), possessing the two exocyclic C=C bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier Delta G(#) 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 ( gt 90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type (SO)-O-... interactions within the S-C=C-C=O entity. The C-13 NMR Delta delta(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)=C(2') bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2') position in the following order: COPh similar to COEt gt CONHPh gt CONHCH2CH2Ph. The decrease of the Delta delta(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 -S- fragment on the polarization of the C=C bonds. (c) 2006 Elsevier B.V. All rights reserved.", publisher = "Elsevier Science Bv, Amsterdam", journal = "Journal of Molecular Structure", title = "H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond", volume = "800", number = "1-3", pages = "85-92", doi = "10.1016/j.molstruc.2006.03.075" }
Marković, R., Baranac-Stojanović, M., Juranić, N., Macura, S., Cekic, I.,& Minić, D. M.. (2006). H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond. in Journal of Molecular Structure Elsevier Science Bv, Amsterdam., 800(1-3), 85-92. https://doi.org/10.1016/j.molstruc.2006.03.075
Marković R, Baranac-Stojanović M, Juranić N, Macura S, Cekic I, Minić DM. H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond. in Journal of Molecular Structure. 2006;800(1-3):85-92. doi:10.1016/j.molstruc.2006.03.075 .
Marković, R., Baranac-Stojanović, Marija, Juranić, N., Macura, S., Cekic, I., Minić, Dragica M., "H-1 NMR dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about C=C bond" in Journal of Molecular Structure, 800, no. 1-3 (2006):85-92, https://doi.org/10.1016/j.molstruc.2006.03.075 . .