** The rotational barrier could not be estimated owing to the fact that the fragments across C1-C2 bond are already orthogonal to each other.
The major difference between oximes (Table 1) and NNHOs (Table 2) is that the C1-N bond length and C1-C2 bond length values became relatively smaller after deprotonation. Another significant observation is that the C1-C2 rotational barrier increased by at least 10-20 kcal/mol. The BDE values are significantly smaller in the neutral species. This reduction is due to the fact that C1-C2 bond strength is significantly reduced upon deprotonation in O-1 to O-15 . Also, the two fragments upon dissociation exists independently (Figure 5). These observations imply that the L→C coordination character is quite justifiable in NNHOs. This also implies that these NNHOs are very unstable and they may get dissociated to the NHC and the fulminic acid species easily. Bond dissociation in O-12 gives rise to NHC and aryl cyanide oxide which is a stable species. This could be the reason why no information is available on the nitroso NHO’s in the chemistry of NHO’s. The above study indicates that it is possible to consider the carbene→Fulminic acid coordination interaction in these species as shown in Figure 5 as one of the resonating structures.
Fig 5 . Possible NHC→C interaction in Pralidoxime and its deprotonated form.