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Transition structures for the [l,n]-sigmatropic hydrogen shift in 1-propene (n = 3), (2)-1,3-pentadiene (n = 5), and (32,52)-1,3,5-heptatriene (n = 7) have been studied by using a b initio SCF and correlated wave functions with several basis sets from STO-2G to 6-3 1G*. Antarafacial transition structures were found for propene and heptatriene and suprafacial for pentadiene, as predicted by the Woodward-Hoffmann rules. Activation energies were also obtained and were found to decrease significantly from the [1,3]-to the [ 1,5]-to the [ 1,7]-hydrogen shift in agreement with earlier experimental results. The deuterium isotope effect for the [1,5] shift has been computed a b initio and found in poor agreement with experiment.Sigmatropic rearrangements that involve hydrogen transfer have been of considerable theoretical'-s and experimental6 interest since the stereochemistry of their transition structures was predicted by Woodward and Hoffmann.' They stated that the [ 431-, [ 1,7]-, ... hydrogen migrations would have transition structures corresponding to an antarafacial hydrogen tnigration while the [ 1,5]-, [ 1,9]-, 0.. hydrogen migration would have transition structures with suprafacial stereochemistry. Quite recently Dewar has questioned the synchronous nature of many concerted reactiom8 However, he noted that [ l,n]-sigmatropic rearrangements t h a t involve hydrogen transfer are likely t o be an exception to his rule t h a t "synchronous multibond mechanisms are normally prohibited" and therefore are likely t o have symmetric transition structures.We have undertaken a systematic theoretical study of the [1,3]-, [ 1,5]-? and [ 1,7]-sigmatropic hydrogen-transfer rearrangements in t h e corresponding methyl-conjugated linear polyenes (1-3). Both transition structures and activation energies have been examined. 2 ResultsAll computations were done on Vanderbilt University's DEC-10 and DEC-20 computers with use of Pople's GAUSSIAN so program10 'Permanent address: J. Heyrovsky Institute of Physical and Electrochemistry, Czechoslovak Academy of Sciences, Prague.

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Electrochemical techniques (potentiodynamic polarization curves and electrochemical impedance spectroscoy (EIS) were used to study the effect of dibenzylsulfoxide adsorption on the dissolution of iron in 5% hydrochloric acid. To discuss different proposed mechanisms of dibenzylsulfoxide adsorption at the iron surface a quantum chemical topological method was used, which is suitable for studying the interaction of organic molecules with metal surfaces. Based on the results of the topological modeling, adsorption followed by reduction of dibenzylsulfoxide to sulfide is most favorable. EIS shows the possible effect dibenzylsulfoxide has on the electrochemical desorption of adsorbed hydrogen. Topological studies indicate strengthening of the bond of the adsorbed hydrogen to the metal due to adsorption of the inhibitor.

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