Photochemical decomposition, singlet carbenes

Also, the Wolff rearrangement of diazo Meldmm s acid 33, studied by DFT at the B3PW91/6-311+G(3df,2p) level of theory, proved to be a concerted process because the product of the photochemical or thermal decomposition in methanolic solution was the ketoester 34 (Scheme 3) while the expected products of the singlet carbene 35, for example 36, were not detected <2003JA14153, 2005CJC1382>. 

Tlie decomposition of diazo compounds can be run under very difierem conditions. Their photochemical decomposition has been largely investigated in the gas phase and in solution in the presence of olefinic and saturated hydrocarbons as substrates the fundamental concepts concerning the relative reactivity and selectivity of singlet-triplet states of carbenes are essentially the result of such studies and they have formed the basis for the determination of the correla tion between the spin state of the carbene and its selectivity and reactivity in imerliun and cycloaddition reactions. 

Chapter 7. On the other hand, methylene (rCH ) and alkyl substituted methylenes (carbenes, CHR CR2 R H) can be readily prepared either by the thermal (or photochemical) decomposition of the corresponding diazo compounds (Equation 6.51) themselves prepared from an amine (Chapter 10) or ketone (or aldehyde) (Chapter 9) precursor. Alternatively, for a species that behaves as if it were singlet methylene (rCH ), the treatment of methylene iodide (diiodomethane, I2CH2) with copper (Cu)-activated zinc (Zn) metal (Equation 6.52) can be used (the Simmons-Smith reaction ). 

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