The Relative Stability of Spin States

The relative stability of the different spin states of carbenes may depend considerably on their substituents  

The triplet state is generally the more stable one for CH, the singlet-triplet splitting is 10 kcal/mol (recent calculations) and carbalkoxycarbenes also have a triplet ground state, but in this case is only 7 kcal/mol (14). 

Dichlurocarbene. a carbene which bears n-donating substituent, is a singlet ground state species, where the n lectrons of the Cl groups interact with the empty / -orbita) of the singlet carbene. 

The two classical methods used for generating carbenes are the a-eliminatiun reactions of halogen compounds and the decomposition of diazo compounds. The generation of dichlorocarbene from chloroform under basic conditiorts or from HgCCl2Br by thermal decomposition is a classical example of the first method. 

The second method has received panicular attention because it constitutes 

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