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I know that hyperconjugation stabilises a double bond. But in propene an electron-donating group $(\ce{-CH3})$ is increasing the electron density at the double bond, so its nucleophilicity should be higher. How can it be more stable as well as more reactive?

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  • $\begingroup$ you said more reactive, but with what are you reacting both of them. $\endgroup$
    – TeslaBolt
    Feb 12, 2022 at 11:00
  • $\begingroup$ @TeslaBolt I meant that propene has higher nucleophilicity than ethene. I am reacting them both with the same electrophile. $\endgroup$
    – Satya
    Feb 12, 2022 at 14:03
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    $\begingroup$ What do you mean by "stable"? $\endgroup$
    – user55119
    Feb 12, 2022 at 15:47
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    $\begingroup$ The heats of formation decreases by -5 kcal/mol for every -CH2- group that is added to each homologous. the n-alkanes . This doesn't mean that n-hexane is more stable tha n-pentane. Look here. $\endgroup$
    – user55119
    Feb 16, 2022 at 23:15
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    $\begingroup$ I don't say that. Is benzene more stable than cyclohexene in the presence of bromine? Yes, it ia kinetic difference. Is 1,2,4-tri-t-butylbenzene more stable than cyclohexene in in a UV photochemical reaction ? No, the benzene compound absorbs light to form a Dewar benzene and cyclohexene doesn't. Stability is relative to conditions.. $\endgroup$
    – user55119
    Feb 17, 2022 at 20:53

1 Answer 1

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you need to go with the mechanism.

1st

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in this case propene will form a 2nd degree carbocation which is more stable.

2nd enter image description here

when the electrophile is having a lone pair then a 3 membered ring is formed as intermidiate.then the other Nucleophile attack to open the ring and thus product is formed.

you can refer to Markovnikov's Rule for further info(https://en.wikipedia.org/wiki/Markovnikov%27s_rule)

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