The question asks me to identify the compound which has a stronger double bond. I came up with two kinds of reasoning but they do not agree upon a common answer.

1: $sp^2$ carbons are more electro-negative and they would like to have electron donating groups sitting next to them. So in the compound one , the extra methyl group should increase stability and therefore, one would expect the bond strengths to increase. Thus decreasing the bond length (smaller bond length is more stronger? stronger bonds imply more stability)

2: Since the methyl group partially donates electrons to the $sp^2$ carbon, the $sp^2$ carbon's tendency of pulling the double bond electrons towards itself should decrease. Thus increasing the bond length.

So where am I going wrong?

If you have any good resource/material on strength of bonds, please let me know.

EDIT (another Q):


Which double bond has higher disassociation energy?

  1. Substituted alkene is more stable than unsubstantiated alkene. So I is more stable which means it has higher bond disassociation energy so II must be having lesser bond disassociation energy.

  2. Due to hyper conjugation, the bond order in compound I decreases so it must have lower bond disassociation energy.

Which one is correct among the above two reasoning?


If the electro-negativity difference between the atoms is larger, then the bond will be more ionic and hence should be stronger?


1 Answer 1


Out of the 2 bromo compounds, the first one has has stronger $\ce{C-Br}$ bond, because the lone pair of $\ce{Br}$ is in conjugation with $\ce{C=C}$. In first case I think Compound 1 is more stable for the reason that it has more substituted $\ce{C=C}$. In reasoning 2 I think when you think about decrease in bond order, the tendency of pulling electrons of $sp^2$ carbon has not decreased. Me- group itself donates electrons because Carbon is $sp^2$ hybridised. The tendency will not increase or decrease. I think it will remain in the form of slight polarisation.

  • $\begingroup$ What do you think? $\endgroup$ Jan 24, 2016 at 14:50

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