1,3-dipole

In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms.

They are reactants in 1,3-dipolar cycloadditions.

[1][2] The dipole has at least one resonance structure with positive and negative charges having a 1,3 relationship which can generally be denoted as +a−b−c−, where a may be a carbon, oxygen or nitrogen, b may be nitrogen or oxygen, and c may be a carbon, oxygen or nitrogen.

[3] Known 1,3-dipoles are:

A demonstration that how some well known 1,3-dipoles like ozone, nitro compounds and azides can be shown to have a resonance structure having 1,3 relationship between positive and negative formal charges
Carbonyl oxide