We have 3 products one is cyclobuta-1,2 diene cyclobuta-1,3 diene and the other is cyclo prop-2-en-one, we want to find the stable product out of the 3. So,the third one due to high angle strain, must be unstable, however this is not true as per datas. Even some of the resonance structures of cycloprop2-enone(the one with positive charge on O atom are highly unstable), so I am not able to understand what makes the third one more stable than the first and second products.
Please help.

  • $\begingroup$ I have edited the question, hope it is more understandable can it be reopened again please $\endgroup$
    – green_32
    Apr 21 '21 at 18:27
  • $\begingroup$ One of cyclopropenone's resonance structures has a positive charge in the 3-membered ring (and a negative charge on oxygen) making it aromatic (increased stability) according to Huckel's 4n+2 rule. $\endgroup$
    – ron
    Apr 21 '21 at 19:12
  • $\begingroup$ Please don't edit and practically change the question because those who have already answered do not get a notification. $\endgroup$ Apr 22 '21 at 6:19
  • $\begingroup$ Can anyone please tell why was it downvoted? What improvement should I make in the post? Thanks. $\endgroup$
    – green_32
    Apr 27 '21 at 13:14

In an allene system(two double bonds next to one another) the substituents on either carbon try to be in the plane perpendicular to each other. For reference see this image:


But as we know that a cyclobutane ring is completely planar, it will prevent this phenomenon and will produce a ring strain even more than that in cycloprop-2-en-one.

Now you might wonder why does an allene system tend to behave in such a manner. For that you can refer to @ringo's answer on Why are the two CH2 groups in allene perpendicular to each other? .

Looking up the 3d structures of these compounds on pubchem can also help you.



  • $\begingroup$ Thanks, for the answer, but then what makes cyclobuta-1,3-diene less stable than 2 cyclo propen- one, in this all the carbon atoms have less angle strain than the first one $\endgroup$
    – green_32
    Apr 21 '21 at 11:18
  • $\begingroup$ @green Yes, angel strain is the key here. $\endgroup$ Apr 21 '21 at 14:05
  • $\begingroup$ I didn't understand, so cyclobuta-1,3 diene should be more stable than 2 cyclopropenone as angle strain is less in the former one but this is not true, as per the datas . $\endgroup$
    – green_32
    Apr 21 '21 at 16:37
  • $\begingroup$ @green In the question you mentioned cyclobuta-1, 2 diene and not cyclobuta-1, 3 diene $\endgroup$ Apr 22 '21 at 4:04
  • $\begingroup$ Sorry, but I didn't remove cyclobuta-1,2 diene it is still there, I just added a new product, your answer is still helpful, thanks. I was just wondering what could be reason for cyclobuta-1,3diene $\endgroup$
    – green_32
    Apr 22 '21 at 16:43

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