Question

Please Help!

Write the following "carbocations" in the correct order of their stability, with reasons :

(diagrams, attached)

Answer 1

i would like to know the answer to this too...

Answer 2

Haha :D

Answer 3

http://www.masterorganicchemistry.com/2011/03/11/3-factors-that-stabilize-carbocations/

Answer 4

@aaronq : Here there's something to do with the -i and +i groups..

Here, CN is the strongest -i group, hence I believe it's the least stable.
And, I am confused beyond this :(

Answer 5

what's -i?

Answer 6

aaronq the site you gave us is helpful, but it only shows groups like c=c bonds that are bonded to the cabon with a positive charge directly. So this allows the two p-orbitals to overlap and cause stabalization to occur. In aditi_singh's question, the the c=c/CN bond are not directly bonded to the carbon with the positive charge... they are bonded to another carbon with an sp3 hybridisation, so it "blocks" resonance stabalisation from occuring between the carbon with the positive charge and the c=c/CN bond..

Answer 7

I'm no pro at orgo., but here's my guess. From least stable to most: 1, 4, 2, 3.

#1 is just a secondary carbocation, it's fairly unstable.
#4 can undergo a hydride shift unlike #1 and so it can form a tertiary carbocation.
#2 can undergo the hydride shift and also participate in some resonance with the double bond.
#3 can undergo the hydride shift and also participate in resonance, but there are more pi electrons between the C and the N that can be delocalized, which should make it more stable.

Answer 8

(#3) delocalisation cannot occur because you are bonded to an sp3 hybridised carbon with no P orbital.

Answer 9

@Ezizio, delocalization can occur after a hydride shift from carbon 2 to carbon 3.