# Yield of possible products from acid catalysed hydration of an alkene with a phenyl group

Here, (d) may be the major product due to high temperature.

My questions are:

• Will a kinetically favoured (minor) product (c) form?

• What shall be the order of yield of products?

• d>c>b>a........ Aug 11 '20 at 7:29
• @user600016 why c over b? Also, do you not agree with the answer given below in that case? If so, please take the time to formulate a proper answer or comment on the given answer on why it would be incorrect. Aug 11 '20 at 11:39
• Why do you think c) is the kinetic product? I mean what is your reasoning behind that. Also, acid catalysed hydration reactions are reversible, so the kinetic product would not form in a high yield. Aug 11 '20 at 20:33
• @ShoubhikRMaiti (1) Usually migratory aptitude of phenide > methanide. Hence, (c) will be kinetically favoured. If you have specific data for the order of migratory aptitude for acid catalysed dehydration of alcohols; please share. (2) Yes, because the reaction is thermodynamically favoured, the yield of kinetically favoured will be very low (or it won't from, I don't know). Aug 12 '20 at 4:18

A basic principle in OChem says that stability of intermediate is the key factor in deciding the major product, in general. Another factor is stability of final product.

Will a kinetically favoured (minor) product (c) form?

It will form, as far as it's intermediate is known to exist (and it exists). However, that will be present in very minor amount, as the intermediate of it will not be as stable as that of (b) and (d). Additionally, the stable intermediate of (c) has 7 α-H, while that of (a) has 2 α-H, so product (c) will be major than product (a).

Here, (d) may be the major product due to high temperature.

The intermediates of (b) and (d) are equally stable. So, here we use the second factor. By looking at the structures of product (b) and product (d), we can say that (d) is major product due to extended conjugation and hyperconjugation with 9 α-H. Really?

The answer is YES. It is known that acid-catalyzed hydration reaction is highly exothermic$$1$$, which is why it is favored at low temperatures! (In accordance with the "Le Chatelier's Principle", a system will consume heat when temperature of surrounding is raised).

Now, I think, it's pretty clear what the order of yield of products should be :)

### References

$$1$$: https://en.wikipedia.org/wiki/Hydration_reaction#Alkenes

• In one of your statement, you are comparing the stability of final products i.e. an alcohol and an alkene. Can we really compare two different class of compounds based on conjugation and hyperconjugation? Aug 12 '20 at 4:24
• I don't think that they can't be compared just bcoz they contain two different class. IMO, anything which contributes to stability can be used to decide major product. In addition to this, the side chain in (b) isn't participating in delocalization with ring, unlike many other benzene deriv., so the comparison becomes logical. I would suggest you to take more time. Another example, where stability of conjugate base of two different classes are compared: acidity of phenol and benzoic acid. Aug 12 '20 at 6:00