[5] Both the shortened length of the N−C bond and the longer Se=C bond suggest a delocalization of the lone pair on the amines; the Se=C π-bonding electrons are drawn towards the selenium atom, while the nitrogen's lone pair is drawn towards the carbonyl carbon.

[6] These minor differences suggest that the properties emergent from the delocalized nitrogen lone pair and destabilization of the C=S and C=Se π bond in thiourea and selenourea will also be similar.

While the selone tautomer (I) has been shown to be the more stable form,[7] mainly qualitative and comparative information on selenourea's tautomerization is available.

In comparable manner to ketones, selones also tautomerize: Since the greater delocalization of the lone pair electrons correlates with the selone product, the equilibrium position of selenourea likely has an equilibrium position comparable to thiourea's (which is lies more to the right that than urea's).

Thiourea has been shown to exist predominantly in its thione form at 42 °C in dilute methanol, with the thionol tautomer almost nonexistent at neutral pH.