Lower energy transition state = more stable intermediate?

[Monkeymaniac]

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Is there a corelationship between energies of transition state and intermediate? That is, if a reaction proceeds with two transition states and one intermediate (two crests and one trough in between in G vs. time graph), and if the reaction can proceed in two pathways, does a pathway with higher first activation energy necessarily have higher intermediate energy? Thanks inadvance.

 

[PiBond]

Is there a corelationship between energies of transition state and intermediate? That is, if a reaction proceeds with two transition states and one intermediate (two crests and one trough in between in G vs. time graph), and if the reaction can proceed in two pathways, does a pathway with higher first activation energy necessarily have higher intermediate energy? Thanks inadvance.

transition states are more unstable and therefore are of high energy than intermediates (we can isolate intermediates--by definition, we can't isolate transition states). in the two step reaction you've given, the intermediate would be of lower energy than the transition states and the step in the reaction with the highest activation energy would be the rate determining step.

if a reaction can proceed through two pathways it will take the pathway that is easiest to get through (has the least activation energy in the rate determining step and thus allows more molecules get over the barrier). this is of course assuming that we're dealing with kinetics and not thermodynamics. i'm pretty confident that the pathway with the higher activation energy would also yield the highest energy intermediate as well; but then again, there's always exceptions in science

just my two cents

 

[orgohacks]

transition states are more unstable and therefore are of high energy than intermediates (we can isolate intermediates--by definition, we can't isolate transition states). in the two step reaction you've given, the intermediate would be of lower energy than the transition states and the step in the reaction with the highest activation energy would be the rate determining step.

if a reaction can proceed through two pathways it will take the pathway that is easiest to get through (has the least activation energy in the rate determining step and thus allows more molecules get over the barrier). this is of course assuming that we're dealing with kinetics and not thermodynamics. i'm pretty confident that the pathway with the higher activation energy would also yield the highest energy intermediate as well; but then again, there's always exceptions in science

just my two cents

Good answer, completely agree. It would be reasonable to expect a reaction with a lower activation energy barrier to also have a lower-energy intermediate, but I'd be cautious about calling this a general rule.