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 .
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.