1H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives

Barriers to rotation about C{double bond, long}C bond

R. Marković, M. Baranac, N. Juranić, Slobodan I Macura, I. Cekić, D. Minić

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

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 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-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 ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, 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 13C NMR ΔδC(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 > CONHCH2CH2Ph. The decrease of the ΔδC(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.

Original languageEnglish (US)
Pages (from-to)85-92
Number of pages8
JournalJournal of Molecular Structure
Volume800
Issue number1-3
DOIs
StatePublished - Dec 4 2006

Fingerprint

alkylidene
Isomerization
Isomers
isomerization
isomers
Hot Temperature
Nuclear magnetic resonance
Derivatives
nuclear magnetic resonance
Electrons
Energy barriers
Nuclear magnetic resonance spectroscopy
Temperature
Hydrogen bonds
electrons
Hydrogen Bonding
Dimethyl Sulfoxide
fragments
Polarization
Magnetic Resonance Spectroscopy

Keywords

  • 4-Oxothiazolidines
  • H NMR spectroscopy
  • Rotational barrier
  • Z/E-isomerization

ASJC Scopus subject areas

  • Structural Biology
  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Spectroscopy
  • Atomic and Molecular Physics, and Optics
  • Materials Science (miscellaneous)

Cite this

1H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives : Barriers to rotation about C{double bond, long}C bond. / Marković, R.; Baranac, M.; Juranić, N.; Macura, Slobodan I; Cekić, I.; Minić, D.

In: Journal of Molecular Structure, Vol. 800, No. 1-3, 04.12.2006, p. 85-92.

Research output: Contribution to journalArticle

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abstract = "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 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-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 ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, 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 13C NMR ΔδC(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 > CONHCH2CH2Ph. The decrease of the ΔδC(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.",
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AU - Juranić, N.

AU - Macura, Slobodan I

AU - Cekić, I.

AU - Minić, D.

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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 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-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 ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, 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 13C NMR ΔδC(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 > CONHCH2CH2Ph. The decrease of the ΔδC(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 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-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 ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, 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 13C NMR ΔδC(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 > CONHCH2CH2Ph. The decrease of the ΔδC(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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