On reaction of diazomethane with ethene a carbene is formed as a intermediate . This carbene then attacks on the double bond and form cyclopropane . However I read that both singlet and triplet carbene can react in this reaction but according to me since the carbon of carbene is overlapping with two different orbitals hence each electron of carbene must be in different orbital hence must be triplet. I can't find a reference to this on the internet, perhaps you all could help me . enter image description here

  • $\begingroup$ part of the answer may be given here chemistry.stackexchange.com/questions/50277/… $\endgroup$ – porphyrin Apr 14 '17 at 6:40
  • $\begingroup$ I think a triplet carbene reacts in a stepwise fashion rather than a pericyclic concerted cyloaddition as in the singlet case. The triplet adds to one side then a spin flip must occur before radical combination. This leaves the possibility for stereochemical change $\endgroup$ – RobChem Apr 14 '17 at 11:17
  • $\begingroup$ This earlier answer may be helpful. $\endgroup$ – ron Apr 14 '17 at 13:59
  • $\begingroup$ Ron I understood that part and thanks for help but my question is still unanswered that how come if carbon of carbene has to overlap with two different orbitals of two carbon atoms $\endgroup$ – Apoorv Jain Apr 14 '17 at 14:10
  • $\begingroup$ Then how can singlet carbene be possible .( Please see the previous three comments including this one as one ) $\endgroup$ – Apoorv Jain Apr 14 '17 at 14:12

Diazomethylene is singlet therefore carbene is formed in the singlet state. singlet carbene is highly reactive therefore it goes through reaction probably before intersystem crossing (depends on competitive speeds). this is why singlet state of carbene is usually invisible. Triplet carbenes react like radicals unlike singlet state (besides some aryl carbenes) therefore the products are different. you can look up Skell-Woodworth for reaction of different spin states of carbenes. based on the products you can find which spin state of the carbene has been involved in the reaction.


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