Isomerization Mechanism in Hydrazone-Based Rotary Switches: Lateral Shift, Rotation, or Tautomerization?
Two intramolecularly hydrogen-bonded aryihy- drazone (aryl = phenyl or naphthyl) molecular switches have been synthesized, and their full and reversible switching between the E and Z configurations have been demonstrated. These chemically controlled configurational rotary switches exist primarily as...
| Publicado en: | Journal of the American Chemical Society Vol. 133; no. 25; pp. 9812 - 9824 |
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| Autores principales: | , , , , , , |
| Formato: | Artículo |
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American Chemical Society
6/29/2011
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=62654514&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 62654514 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 6/29/2011 vid: 133 iid: 25 pid: 997 pub: American Chemical Society artinfo: ui: 62654514 10.1021/ja200699v ppf: 9812 ppct: 12 formats: tig: atl: Isomerization Mechanism in Hydrazone-Based Rotary Switches: Lateral Shift, Rotation, or Tautomerization? aug: au: Landge, Shainaz M. Tkatchouk, Ekatarina Benítez, Diego Lanfranchi, Don Antoine Elhabiri, Mourad Goddard III, William A. Aprahamian, Ivan affil: Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States Department of Chemistry, Georgia Southern University, Statesboro, Georgia 30458, United States Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, United States Laboratoire de Chimie Bioorganique et Médicinale, Université de Strasbourg, ECPM, UMR 7509 CNRS-UdS, 25, rue Becquerel, 67200 Strasbourg, France Laboratoire de Physico-Chimie Bioinorganique, Université de Strasbourg, Institut de Chimie de Strasbourg, ECPM, UMR 7177 CNRS-UdS, 25, rue Becquerel, 67200 Strasbourg, France su: Hydrogen bonding Isomerization Hydrazones Density functionals Proton transfer reactions Chemical bonds sug: subj: Hydrogen bonding Isomerization Hydrazones Density functionals Proton transfer reactions Chemical bonds ab: Two intramolecularly hydrogen-bonded aryihy- drazone (aryl = phenyl or naphthyl) molecular switches have been synthesized, and their full and reversible switching between the E and Z configurations have been demonstrated. These chemically controlled configurational rotary switches exist primarily as the E isomer at equilibrium and can be switched to the protonated Z configuration (Z-H) by the addition of trifluoroacetic acid. The protonation of the pyridine moiety in the switch induces a rotation around the hydrazone C=N double bond, leading to isomerization. Treating Z-H with base (KCO) yields a mixture of E and "metastable" Z isomers. The latter thermally equilibrates to reinstate the initial isomer ratio. The rate of the Z → E isomerization process showed small changes as a function of solvent polarity, indicating that the isomerization might be going through the inversion mechanism (nonpolar transition state). However, the plot of the logarithm of the rate constant k vs the Dimroth parameter (E) gave a linear fit, demonstrating the involvement of a polar transition state (rotation mechanism). These two seemingly contradicting kinetic data were not enough to determine whether the isomerization mechanism goes through the rotation or inversion pathways. The highly negative entropy values obtained for both the forward (E → Z-H) and backward (Z→E) processes strongly suggest that the isomerization involves a polarized transition state that is highly organized (possibly involving a high degree of solvent organization), and hence it proceeds via a rotation mechanism as opposed to inversion. Computations of the Z E isomerization using density functional theory (DFT) at the M06/cc-pVTZ level and natural bond orbital (NBO) wave function analyses have shown that the favorable isomerization mechanism in these hydrogen-bonded systems is hydrazone-azo tautomerization followed by rotation around a C-N single bond, as opposed to the more common rotation mechanism around the C=N double bond. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2011 holdings: @attributes: islocal: N |
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