Dipolar compound

Example of a dipolar compound, represented by a resonance structure (isocyanide)

In organic chemistry, a dipolar compound or simply dipole is an electrically neutral molecule carrying a positive and a negative charge in at least one canonical description. In most dipolar compounds the charges are delocalized. ^[1] Unlike salts, dipolar compounds have charges on separate atoms, not on positive and negative ions which make up the compound. Dipolar compounds exhibit a dipole moment.

Dipolar compounds can be represented by a resonance structure. Contributing structures containing charged atoms are denoted as zwitterions. ^{[2] [3] [4] [5] [6]} Some dipolar compounds can have an uncharged canonical form.

Types of dipolar compounds

• 1,2-dipolar compounds have the opposite charges on adjacent atoms.
• 1,3-dipolar compounds have the charges separated over three atoms.^[1] They are reactants in 1,3-Dipolar cycloadditions.
• Also 1,4-dipolars ^[4], 1,5-dipolars, etcetera exist.

Examples

• 

  Phosphonium ylide

• 

  Diazomethane

• 

  Carbonyl oxide

See also

• Zwitterion
• Ylide
• 1,3-dipole
• 1,3-Dipolar cycloaddition
• Betaine

References

1. ^ ^{a b} IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "dipolar compounds".
2. ^ Braida et al.: A clear correlation between the diradical character of 1,3-dipoles and their reactivity toward ethylene or acetylene.; J. Am. Chem. Soc.; 2010 Jun 9;132(22):7631-7
3. ^ Hartmann and Heuschmann: Isolation of a Zwitterion in a Diels–Alder Reaction with Inverse Electron Demand; Angewandte Chemie; september 1989; Volume 28, Issue 9, pages 1267–1268
4. ^ ^{a b} MacHiguchi, Takahisa; Okamoto, Junko; Takachi, Junpei; Hasegawa, Toshio; Yamabe, Shinichi; Minato, Tsutomu (2003). "Exclusive Formation of α-Methyleneoxetanes in Ketene−Alkene Cycloadditions. Evidence for Intervention of Both an α-Methyleneoxetane and the Subsequent 1,4-Zwitterion". Journal of the American Chemical Society 125 (47): 14446. doi:10.1021/ja030191g. PMID 14624592. 
5. ^ IUPAC: Preferred IUPAC Names; Chapter 7, September 2004, pp. 56-70
6. ^ Rolf Huisgen (IUPAC): Cycloaddition mechanism and the solvent dependence of rate; Pure & Appl. Chem.; 1980, Vol.52, pp.2283—2302.