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. The dipole has at least one resonance structure with positive and negative charges having a 1,3 relationship which can generally be denoted as , where a may be a carbon, oxygen or nitrogen, b may be nitrogen or oxygen, and c may be a carbon, oxygen or nitrogen. Known 1,3-dipoles are:
 Azides ()
 Ozone ()
 Nitro compounds ()
 Diazo compounds ()
 Some oxides
 Azoxide compounds (RN(O)NR)
 Carbonyl oxides (Criegee zwitterions)
 Nitrile oxides ()
 Nitrous oxide ()
 Nitrones ()

 Some imines:
 Azomethine imine
 Nitrilimines (, analogous to nitrile oxide)
 Carbonyl imines
 Some ylides
 Azomethine ylide
 Nitrile ylide ()
 Carbonyl ylide
 Thiosulfines ()

References

Organic chemistry