The properties of three-membered rings are related to strain, due to the low bond angles. Angular strain gives rise to opening reactions to form acyclic products.

In this section we will study the following heterocycles: oxirane, thiirane, 2H-azirine, aziridine, dioxirane, oxaziridine, 3H-diazirine and diaziridine.

Boiling point: 10.5ºC
Ring stress: 114 KJ/mol
dipole moment: 1.88 D
Characteristics: Colorless liquid, soluble in water, very poisonous in the gas phase.

Boiling point: 55ºC
Ring stress: 83 KJ/mol
dipole moment: 1.66 D
Characteristics: Colorless liquid, partially soluble in water.

Boiling point:
Ring stress: 170 KJ/mol.
dipole moment:
Characteristics: Very unstable substance, with high reactivity in the C=N bond

Boiling point: 57ºC
Ring stress: 113 KJ/mol.
dipole moment: 1.89 D
Characteristics: Colorless liquid, soluble in water, poisonous, with an ammonia-like odor.