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DLS
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Which carbo cation is least likely to form as as intermediate?
|dw:1360852772005:dw|
shubhamsrg
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D) maybe ?
shubhamsrg
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A) is 3 degree and so is C)
shubhamsrg
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B is 2 degree, also has a double bond which adds to the stability
DLS
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its definitely not A for sure
DLS
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C is not 3 degree i guess
shubhamsrg
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C is attached to 3 carbons ?
DLS
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its bridgehead
shubhamsrg
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hmm ? well still there are 3 carbons !
shubhamsrg
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If i had to put a guess, I'd say D)
DLS
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ITS C DAMMIT
shubhamsrg
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hmm,, sorry about that then! :|
DLS
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man I really thought u shud know all that before 2 months of JEE LOL
DLS
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hmm okay sorry :P
shubhamsrg
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Wish your thinking was true!
shubhamsrg
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Well I have never seen a bridged carbocation before.
DLS
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are u freaking kidding me ._.
shubhamsrg
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On a bridge head a positive carbon never occurs
~Wikipedia
DLS
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so what :P
shubhamsrg
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hmm, that is why it must be least likely to form! hmm, seems legit
DLS
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wtf
shubhamsrg
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:)
DLS
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whaaaaaaaaaaat
DLS
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thoda detail zara?
shubhamsrg
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well since bridged carbocation is not formed, hence it is least likely to be formed here.
shubhamsrg
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never formed*
DLS
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i asked why it isnt form ._.
i dont want to accept it as a fact
DLS
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formed*
shubhamsrg
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I don't know the fact! I just learnt it!
shubhamsrg
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reason of the fact*
DLS
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\m/
DLS
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god i cant read that whole thing :/
shubhamsrg
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learn as fact! thats what I just did !
shubhamsrg
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In chem, most of times, there aren't reasons, there are rules, !
DLS
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rehne de be :P
shubhamsrg
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sure! :D
Yahoo!
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Shuld nt the answer be D............
chmvijay
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i think answer is D
DLS
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its C
DLS
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and its proven I guess
DLS
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@abb0t
abb0t
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If (A) is benzene, then it's (D). Remember you can't form primary carbocations ever.
DLS
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answer is C?
DLS
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wikipedia says too..
DLS
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but i want smt more detailed
abb0t
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Wikipedia says the answer is C?
DLS
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On a bridge head a positive carbon never occurs
~Wikipedia
abb0t
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The + isn't on the bridge though.
DLS
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that is why it cant resonate,the charge is localized.
DLS
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so isnt C in a worse condition than D? it cant resonate at all but D still can
abb0t
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Resonance is not the same as formation of a carbocation
DLS
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its about the stability of the carbocation
abb0t
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Resonance just tells you where electron behaves or forms a more stable structure
DLS
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more resonating structures=more stable
C h as 0 resonating structures
DLS
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D has one if you see
abb0t
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Draw them for acetylene.
DLS
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|dw:1360961235810:dw|
not sure duh
abb0t
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I don't think that would work. Did you move the hydrogen?????
DLS
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idk man
abb0t
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Resonance is only movement of the electron. Not protons.
DLS
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so whatnow
abb0t
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Maybe @BluFoot can help right now
I'm not on my comp so I can't give detailed answers right now and don't have my notes w/ me. If you're on later I will explain better if no1 else has helped you. I gtg
DLS
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hmm okay
BluFoot
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A is very stable because of all the resonance from the phenyl groups.
B is kinda stable from the resonance of the double bond. This is called an "allylic carbocation"
http://science.uvu.edu/ochem/index.php/alphabetical/a-b/allylic-carbocation/
C has no resonance, but it's tertiary at least
D is definitely the least stable. Vinylic carbocations (+ on the C=C) are reaalllllllyyyy unstable. The reason is based in orbitals. C=C are sp2, but with a carbocation it becomes sp. sp orbitals are situated close to the nucleus, so the positive charge is very close to the nucleus, which is positive, so it's unstable
DLS
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okay,thanks :D
BluFoot
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I've never seen the structure in C btw... do you know what it's called?
DLS
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ive been taught its bridgehead carbon (out of the plane)
BluFoot
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Oh right, I haven't learned about those. It's still probably D but don't make my word for it since I know nothing about the bridges.
DLS
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its C idk why....
BluFoot
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I have no idea, sorry :/
abb0t
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It's a bicyclo compound.
abb0t
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Well, "C" would form a radical rather than a carbocation since it's an all hydrocarbon structure. That could be one argument.
I'm not entirely sure about this one to be honest. But I can't help but also think the answer could be D since you don't usually ever have primary carbocations. And there's no type of resonance in structure D. If you take out the double bond, you'd have another charge and that would definitely form a very thermodynamically unstable structure. It would definitely prefer to stay.
aaronq
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If the answer was to be C, then, i imagine that'd it would be because the strain put on it by it's inability to undergo an sp2 conformation (180 degree angles) since it's fixed on the frame and it would make of high energy/unstable