Triplet ground state carbonylnitrenes

Harrison and Shalhoub131 have recently investigated the related carbonylnitrenes HCON, FCON, MeCON, and MeOCON, finding a triplet ground state in all cases. Geometry optimizations were carried out using an STO-3G basis set. 

However, the opposite conclusion from that drawn for aroylnitrenes was made about ground-state multiplicity of aroyloxynitrene 23. An ESR spectrum attributable to triplet (4-acetylphenoxy) carbonylnitrene ( 23) was detected at 8 K after irradiation of a suspension of 22 in fluorolube at 77... 

Therefore, the experimental data are most consistent with a singlet ground state of carbonyl nitrenes. Triplet carbonylnitrenes were not detected in either chemical trapping or spectroscopic experiments. The explanation of these resnlts was available only recently. 

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