01761nas a2200157   4500008004100000022001400041245007600055210006900131260007100200300001400271490000800285520116300293100002201456700001601478856010901494       2012                        eng d  a1089-563900aViscosity dependence of intra- and intermolecular diels-alder reactions0 aViscosity dependence of intra and intermolecular dielsalder reac  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcFEB  a1191-11980 v1163 a<p>The kinetics of the bimolecular Die Is Alder reaction between anthracene-9-carbinol and N-ethyl maleimide have been studied in a series of pyridinium-based ionic liquids with the tetrafluoroborate ([BF4](-)) and the bis(trifluorosulfonimide) ([NTf2](-)) anions and the viscosity dependence of the rate constants have been compared with the results for the intramolecular Diels Alder reaction of (E)-1-phenyl-4-[2-(3-methyl-2-butenyloxy)benzylidene]-5-pyrazolone. The comparison leads to the surprising observation that the intermolecular reaction is less susceptible to viscosity variations of the ionic liquids as compared to the intramolecular reaction. The observed similarities and differences emphasize the complicated nature of solvent friction on the kinetics of cycloaddition reactions. The results are explained by considering the bimolecular and intramolecular processes as cases of translational and rotational diffusion, respectively. Plausible indicators of microviscosity consistent with the kinetic data for the Diels-Alder reactions are briefly discussed along with the constraints involved in designing a general microviscosity scale.</p>1 aTiwari, Shraeddha1 aKumar, Anil  uhttps://library.ncl.res.in/content/viscosity-dependence-intra-and-intermolecular-diels-alder-reactions-0