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Determination ofsyn/anti Isomerism in DCNQI Derivatives by 2D Exchange Spectroscopy: Theoretical Underpinning by Fernando P. Cossío; Pilar de la Cruz; Antonio de la Hoz; Fernando Langa; Nazario Martín; Pilar Prieto; Luis Sánchez is a Chemistry article available to read on EtoBox.

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The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional exchange spectroscopy (2D EXSY). The isomers formed were characterised by 1 H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16-13.93 kcal/ mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41-14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experi-[a

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Author

Fernando P. Cossío; Pilar de la Cruz; Antonio de la Hoz; Fernando Langa; Nazario Martín; Pilar Prieto; Luis Sánchez

Publisher

John Wiley and Sons; Wiley (John Wiley & Sons); John Wiley & Sons Ltd.; Wiley (ISSN 1434-193X)

Published

2000

Language

EN

Field

Chemistry (Physical Sciences)