Table 3. Relative energy differences (ΔE) between ground (nitro) and metastable (exo- and endo-nitrito) states computed using the QM/MM approach and for the optimized isolated-molecule geometries.

Computations were performed at the DFT(B3LYP)/6-311++G** level of theory.

Form	ΔE rel (kJ mol−1)
	QM/MM	Isolated molecule
Nitro	0.0	0.0
Endo-nitrito	+18.0	+5.3
Exo-nitrito	+31.2	+11.9