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Here is a question from my textbook:-

Q - Give the major product formed by the heating of the following ether with HI.

         CH3
         |
CH3-CH2-CH-CH2-O-CH2-CH3

According to me, The product should be this due to Delocalisation of +ve charge among the neighbouring Carbon atoms.

         CH3
         |    
CH3-CH2-CH-CH2-I + CH3-CH2-OH

I checked the answer in my book and it is completely different:-

         CH3
         |
CH3-CH2-CH-CH2-OH + CH3-CH2-I

Now, I think they may have considered Steric Hindrance to be the factor of attack of OH but will not Delocalisation be dominant over Steric Effect?

Also, What will be the effect of Hyperconjugation on the reaction? Please Guide Me.

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Your ether has $\ce{CH2}$ groups at both sides of the oxygen atom.

I would exclude a $S_N1$ reaction here! Instead, cleavage of the ether proceeds via $S_N2$. The oxonium ion resulting from addition of a proton is attacked by iodide at the least hindered carbon atom. Iodide is quite big ;-)

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  • $\begingroup$ So that means that they indeed has taken steric effect to be the factor. $\endgroup$ – Sharad Gautam May 18 '15 at 18:17
  • $\begingroup$ @SharadGautam Yes, absolutely. $S_N1$ reactions would give two primary cations with little stabilisation here. $\endgroup$ – Klaus-Dieter Warzecha May 18 '15 at 18:23
  • $\begingroup$ How will Hyperconjugation affect the reaction? $\endgroup$ – Sharad Gautam May 19 '15 at 8:26
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According to me, The product should be this due to Delocalisation of +ve charge among the neighbouring Carbon atoms.

Even if you consider a $S_N1$ reaction pathway for this reaction, the positive charge could be more stable on the $\ce{-CH2CH3}$ branch as it has 3 hyperconjugation structures stabilizing the positive charge against 1 in the other branch. And gives the same products.

Moreover, as Klaus Warzecha said, steric hindrance comes into the play while considering $S_N2$ pathway which looks a more plausible pathway due to the the relatively unstable primary carbocations that form in $S_N1$

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