I'm getting results from a transition state guess software, in which the number of intermediates are two and there's only one transition state for a reaction, is that possible?
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3$\begingroup$ In principle you could have a barrier-less process, but it sounds quite fishy. I guess it depends on your reaction. Can you say more? $\endgroup$– ZheCommented Dec 27, 2016 at 15:23
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1$\begingroup$ I'm attaching an image of the reaction (Michael Addition reaction) and the energy profile diagram that I'm getting for this reaction, I'm asking here that does this energy profile diagram makes sense? $\endgroup$– user39222Commented Dec 28, 2016 at 7:05
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$\begingroup$ I've seen a couple of inorganic metal complexes reactions where the total no. of intermediates are more than the total no. of transition states, I'm trying to figure out if that's also possible for this particular reaction. $\endgroup$– user39222Commented Dec 28, 2016 at 7:10
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$\begingroup$ @Zhe like radical recombinations? $\endgroup$– Eashaan GodboleCommented Dec 28, 2016 at 18:03
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$\begingroup$ @EashaanGodbole That would be an example, but your reaction does not seem such a process. Bonds are breaking and forming at the same time, so I would assume there is an intermediate. You can try an IRC search. $\endgroup$– ZheCommented Dec 28, 2016 at 18:56
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2 Answers
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Let's assume your reactive complex (reactants interacting) are optimised, i.e. its gradient equals zero, and your potential energy surface is continuous.
Then any direction is either uphill or constant (otherwise the optimisation hypothesis would not apply). There are three possibilities: (a) going from reactants to intermediate gives a transition state which has higher energy than both reactive complex and intermediate; (b) reactants and intermediate lie on a plateau where energy does not change; or (c) one hypothesis is wrong.
So yes, for barrierless processes.
answered Feb 6, 2017 at 21:01
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Completely normal, especially for a bimolecular process forming and adduct like that. However, you shouldn't be applying transition state theory for this kind of process - variational methods (minimising the reaction rate) are more accurate.
These systems can be treated very efficiently using energy grained master equation with RRKM theory, for example software packages look at Mesmer or Paper.
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1$\begingroup$ This answer has nothing to do with the question since it doesn't answer the if it's possible to go from reactants to product/intermediate without going through a higher energy state. $\endgroup$– DSVACommented Jan 28, 2017 at 16:56