** 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.