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cyclopentanone is treated with piperidine in acid catalyzed conditions to form the organic product (A). (A) on reaction with benzyl bromide followed by hydrolysis gives another organic product (B) containing aromatic ring. If the sum of degrees of unsaturation of (A) and (B) is x and the difference of the number of carbon atoms in (A) and (B) is y, then find the value of x/y.

According to me compound (A) is an enamine, but I'm not sure about (B)!

my attempt

So according to this, my answer is x/y = 10/7 But the actual answer is x/y = 4.5

I don't know where am I going wrong!

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    $\begingroup$ What reactions do enamines undergo? They are isoelectronic with enolates. $\endgroup$
    – user55119
    Jun 1, 2020 at 15:47
  • $\begingroup$ If you have a enolate and alkyl halide in a mixture, what product you expect to have? $\endgroup$
    – Mathew Mahindaratne
    Jun 1, 2020 at 15:50
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    $\begingroup$ A ketone with some extra carbons than the enolate! $\endgroup$
    – Yashwini
    Jun 1, 2020 at 15:51
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    $\begingroup$ Structure given for (B) is not quite correct. Your question says "(A) on reaction with benzyl bromide followed by hydrolysis gives another organic product (B)." Then what happens to the hydrolysis? $\endgroup$
    – Mathew Mahindaratne
    Jun 1, 2020 at 15:55
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    $\begingroup$ Exactly so, you regenerate the ketone $\endgroup$
    – Waylander
    Jun 1, 2020 at 16:00

1 Answer 1

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As per the reaction sequence what you said about A is absolutely correct and in B I think you didn't consider hydrolysis of the product. The product what you have written is correct before hydrolysis, and after hydrolysis the carbonyl reforms and the other component becomes piperidine again. So,the final product B is 2-(phenylmethyl)cyclopentan-1-one. Hope that helps!

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