Figure 4.

RSNO resonance structures, balanced between the neutral (center), the zwitterion (left) and the ion pair (right) forms. The trans conformer is depicted here, but the cis is also possible though less stable, as mentioned in section Physical Models for S-nitrosothiols (RSNOs). The neutral form is the most abundant one, the other ones being only minor conformations with dramatically opposite features—hence the dual reactivity of RSNOs with nucleophiles. The relative abundance of the three RSNO forms is highly depend on its microenvironment and the nature of the R group. For instance, the neutral/zwitterion/ion pair ratio is 79/11/10% vs. 75/15/10% for HSNO and CH₃SNO respectively.