Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions. In most dipolar compounds the charges are delocalized; however the term is also applied to species where this is not the case. 1,2-Dipolar compounds have the opposite charges on adjacent atoms. The term 1,3-dipolar compounds is used for those in which a significant canonical resonance form can be represented by a separation of charge over three atoms (in connection with 1,3-dipolar cycloadditions). Subclasses of 1,3-dipolar compounds include:
- Allyl type X=Y+–Z−↔︎ X−–Y+=Z↔︎ X+–Y–Z−↔︎ X−=Y–Z+ (X, Z = C, N, or O; Y = N or O)
See: azo imides, azomethine imides, azomethine ylides, azoxy compounds, carbonyl imides, carbonyl oxides, carbonyl ylides, nitro compounds, nitrones
- Propargyl type X≡N+–Z−\(\leftrightarrow\) X−=N+=Z\(\leftrightarrow\) X−=N–Z+\(\leftrightarrow\) X–N=Z (X = C or O, Z = C, N, or O)
See: azides, diazo compounds, nitrile imides, nitrile oxides, nitrile ylides, nitrilium betaines
- Carbene type X:–C=Z\(\leftrightarrow\) X+=C–Z− (X = C or N; Z = C, N, or O)
See: acyl carbenes, betaines, imidoyl carbenes, vinyl carbenes