Question

Please help with question #3

Discuss in your own words) how the change from gas phase to aqueous solution can cause each of these observed effects. 3. A mechanism for alkene arylation by palladium (11) is given below. The isotope effect kw/ko was found to be 5 when benzene-De was used. On the other hand, when styrene-2,5-D2 was sued, no isotope effect was observed. Which step in the mechanism below has to be the Rate-Determining Step, based on these observations?? Explain your reasoning thoroughly in your own words). + PACO CCH3)2 k1, Ph–PdO,CCHA + CH3CO,H Ph--PdOCCH, + PhCH=CH, #2Ph-Pd-CH=CHPh + CH,CO,H Ph-Pd-CH=CHPh & PhCH=CHPh + Pd

Answer 1

The concept required to answer this question is that: if a C-H bond breaking is involve in rate determining step, than replacing H with D will result in decreasing the rate of reaction in other words kH/kD will be greater than 1.

Now, in given case the when H of benzene is replaced with D, kH/kD is 5, which means the step involving breaking of benzene C-H bond is rate determining step. Hence

First step of the reaction is rate determining step

Ph-H (benzene) + Pd(O2CCH3)2 ------k1-----> Ph-PdO2CCH3 + CH3CO2H

Is rate determining step.

Thank you