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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: cupid.callin on November 25, 2010, 12:08:39 PM

Title: A few MCQ of Organic
Post by: cupid.callin on November 25, 2010, 12:08:39 PM

Hi all,

These are a few organic questions i couldn't get.

For Ques 1 part (a) ans. is given : E>F>G>A
I guess F should be greater than E as +M effect of Cl will be absent there plus -I effect will make it more acidic.

For pic 2 A is very obvious, but B ... i have no idea what will happen oh heating.

For third pic ... I guessed previously that A will be made as H+ will attack OH forming A, but it wasnt so, answer was C. It is only possible when H+ attack unsaturated system. but why??? if it attacks OH, a 3 degree allylic catbocation will be formed,,, what can be more stable than that??? Please explain it to me!!!!

And the last one ... I have NOOOOOOOOOOOOOO IDEA AGAIN!!!

Title: Re: A few MCQ of Organic
Post by: cupid.callin on November 25, 2010, 12:10:05 PM

i know too many pics made loading slow...

Sorry for that...

Title: Re: A few MCQ of Organic
Post by: orgopete on November 25, 2010, 04:10:19 PM

1) Electrophilic substitution rates can be a good way to estimate the strength of donation and withdrawal. Chlorobenzene is an o/p director, but slower than benzene. Hence, I usually argue that it is a resonance donor to control regiochemistry, but rates indicate that it is reluctant to do so. Therefore the resonance effect is weak.

2) Acetate elimination to alkene, it must have been in your textbook.

3) I expected cyclopentene, but that wasn't a choice. I am guessing hydration of the double bond first, then a pinacol rearrangement.

4) 2x Claisen rearrangements. That might have given something like B, but I think your textbook is wrong on this. It should have been ¹⁴CH₂O.

Title: Re: A few MCQ of Organic
Post by: cupid.callin on November 26, 2010, 04:18:25 AM

2) no i never saw it in my textbook ... can you please explain it to me?

3) But why will it attack double bond. the carbocation formed on attack on OH  is 3 degree and also allylic ... also 2 lone pairs of O are much more basic than a double bond!!! I got the product as C on attack on double bond but why will it attack double bond?

4) i thought the same... i thought book is correct so i am getting something wrong!!!!

Title: Re: A few MCQ of Organic
Post by: orgopete on November 26, 2010, 09:17:35 AM

2) http://www.organic-chemistry.org/synthesis/C2C/alkenes/syn-eliminations.shtm

3) I agree with you. No reference is given so I don't even know if the product is correct. This could have been a hypothetical reaction. I was wrong to suggest cyclopentene after drawing it on paper.

Title: Re: A few MCQ of Organic
Post by: cupid.callin on November 29, 2010, 11:11:57 AM

Thanks!!!!

i'll try to find ans. to third one and get back to you if i could!!!!