4
$\begingroup$

Which of the following should have the longest c=c?

$$\begin{align} \text{a)}\ \ \ \ &\ce{CH2=C=CH2}\\ \\ \text{b)}\ \ \ \ &\ce{CH3 -CH=CH2}\\ \\ \text{c)} \ \ \ \ &\ \ \ \ \ \ \ \ \ \ \ \ce{CH3} \\ &\ \ \ \ \ \ \ \ \ \ \ \ | \\ &\ce{CH3 -C -CH=CH2}\\ &\ \ \ \ \ \ \ \ \ \ \ \ | \\ &\ \ \ \ \ \ \ \ \ \ \ \ce{CH3} \\ \\ \text{d)}\ \ \ \ &\ce{CH3 -C=CH2} \\ &\ \ \ \ \ \ \ \ \ \ \ \ | \\ &\ \ \ \ \ \ \ \ \ \ \ \ce{CH3} \\ \end{align}$$

I know that single bond > double > triple length-wise, but how do you distinguish between double bonds?

$\endgroup$
  • 3
    $\begingroup$ I edited your post to replace the picture with typeset structures. $\endgroup$ – Ben Norris Dec 22 '15 at 19:19
  • $\begingroup$ how do you make structures like this? $\endgroup$ – Prakhar Dec 24 '15 at 4:32
  • $\begingroup$ The basics are on this help center page, with some more advanced stuff at this meta post. The use of the {align} environment and control of spacing to create multi-line structures took some practice. $\endgroup$ – Ben Norris Dec 24 '15 at 12:26
5
$\begingroup$

You can draw Hyper conjugating Structures to compare bond length. More the $\alpha$ Hydrogen of alkene, more are the Hyper conjugating structures, more is the delocalization of π-bond and more is the bond length (since double bond character decreases, bond length increases) Therefore answer should be (d). Hope it helps !

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.