https://doi.org/10.1351/goldbook.Y06728
Compounds in which an anionic site Y− (originally on carbon, but now including other atoms) is attached directly to a heteroatom X+ (usually nitrogen, phosphorus or sulfur) carrying a formal positive charge. They are thus 1,2-dipolar species of the type RmX+–Y−Rn. If X is a saturated atom of an element from the first row of the periodic system, the ylide is commonly represented by a charge-separated form; if X is a second, third, etc. row element uncharged canonical forms are available RmX=YRn. If X is an unsaturated atom, doubly bonded to another first row element Z, the negative charge on Y may be stabilized by π- Z−–X+=YRn. Such ylides belong to the class 1,3 Ph3P+=CH2 (often called a Wittig (CH3)2S+–C−HPh. Note that ylide is a complete word, not to be confused with the suffix -ylide, used for some radical anions. Subclasses of ylides: Ylides RmX+–C−R2 having the negative charge on carbon are classified by citing the name of the element X before the word ylide. E.g. nitrogen ylide, RmX=Y (Y = O, S, Se, Te, NR) are usually named by citing the name of RmX followed by the
conjugation
, Z=X+–Y−Rndipolar compounds
. However, 1,3-dipolar compounds
with only sextet-containing canonical forms (e.g. vinylcarbenes
) are not ylides. E.g. Ph3P+–C−H2reagent
), (CH3)3N+–C−H2, RC≡N+N−–R, (CH3)2S=CHPhphosphorus ylide
, oxygen ylide
, sulfur ylide. A further specification may be achieved by citing the class name of RmX before the word ylide. Thus nitrogen ylides include amine ylides
, R3N+–C−R2, azomethine ylides
R2C=N+R–C−R2, nitrile ylides
, RC≡N+–C−R2. Some authors, who wish to express the positive charge on X, prefer e.g. ammonium ylides
over amine ylides
; such usage varies according to the heteroatom X and to national custom. The ylides RmX+–Y−additive
nomenclature term for Y (oxide, sulfide, selenide, telluride, imide, respectively). E.g. amine imides
; use of the less systematic synonyms amine imines
and aminimines is discouraged. Some classes of ylides are known by trivial names e.g. nitrones
, Wittig reagents
(synonymous with phosphonium ylides
).See also:
betaines
, dipolar compounds
Sources:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1176 [Terms] [Paper]
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1375 [Terms] [Paper]
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1176 [Terms] [Paper]
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1375 [Terms] [Paper]