A ylid or ylide (US) is a neutral molecule with a positive and a negative charge on adjacent atoms. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny They appear in organic chemistry as reagents or reactive intermediates. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation A reagent or reactant is a substance or compound consumed during a Chemical reaction. A reaction intermediate or an intermediate is a Molecular entity that is formed from the reactants (or preceding intermediates and reacts further to give the directly

A ylide is accompanied to some extent by (and often depicted as) its double bonded resonance structure:

The actual electron distribution in the bond depends on the entire molecular structure. Resonance in Chemistry is a theory used to represent and model certain types of non-classical Molecular structures Resonance is a key component

Contents 1 Preparation of a phosphonium ylide 2 Ylide types 3 Ylide reactions 4 References

Preparation of a phosphonium ylide

An ylide can be prepared rather straightforwardly. Typically, triphenylphosphine is allowed to react with an alkyl halide in a mechanism analogous to that of an S_N2 reaction. This forms a alkyltriphenylphosphonium salt which is then allowed to react with a strong base to form the ylide.

The salt products are not shown. Also, the product shown here is shown in the ylide form; however, it could also be shown as the phosphorane form in which the bond to phosphorus is a double bond with the methylene group. Due to an inductive effect, the trio of phenyl groups allows phosphorus to bear such a buildup of positive charge and shifts the negative charge to carbon, creating a reactive species.

Due to the S_N2 mechanism, a less sterically hindered alkyl halide reacts more favorably with triphenylphosphine than an alkyl halide with significant steric hindrance (such as tert-butyl bromide). Because of this, there will typically be one synthetic route in a synthesis involving such compounds that is more favorable than another.

Ylide types

• The most common ylids are phosphonium ylids, used in the Wittig reaction for double bond synthesis from carbonyl groups (C=O). The Wittig reaction is a Chemical reaction of an Aldehyde or Ketone with a triphenyl phosphonium ylide (often called a Wittig reagent In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen The positive charge in these Wittig reagents is carried by a phosphorus atom with three phenyl substituents and one bond to a carbon bearing a negative charge and two substituents, commonly alkyl groups. The Wittig reaction is a Chemical reaction of an Aldehyde or Ketone with a triphenyl phosphonium ylide (often called a Wittig reagent Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 In Organic chemistry, the phenyl group or phenyl ring (often abbreviated as -Ph) is the Functional group with the formula - Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 An alkyl is a Univalent radical consisting of Carbon and Hydrogen atoms arranged in a chain Ylids can be 'stabilised' or 'non-stabilised'. Non-stabilised ylids react readily with both aldehydes and ketones whereas stabilised will only react with aldehydes. An aldehyde is an organic compound containing a terminal Carbonyl group. A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or

• Other common ylids include sulfonium ylids and sulfoxonium ylids, for instance the Corey-Chaykovsky reagent used in the preparation of epoxides or in the Stevens rearrangement. The Johnson-Corey-Chaykovsky reaction is a Chemical reaction in which a Carbonyl is converted to an Epoxide by the action of a Sulfonium ylide An epoxide is a cyclic Ether with only three ring atoms This ring approximately is an Equilateral triangle, i The Stevens rearrangement in Organic chemistry is an Organic reaction converting Quaternary ammonium salts and Sulfonium salts to the corresponding

• Certain nitrogen-based ylids also exist such as azomethine ylids with the general structure:

These compounds can be envisioned as iminium cations placed next to a carbanion. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 An iminium Salt or Cation in Organic chemistry has the general structure + and is as such a protonated or substituted A carbanion is an Anion in which Carbon has an unshared pair of Electrons and bears a negative charge usually with three substituents for a total of eight The substituents R₁, R₂ are electron withdrawing groups. In Organic chemistry, a substituent is an atom or group of atoms substituted in place of a Hydrogen atom on the Parent chain of a Hydrocarbon The Polar effect or electronic effect in Chemistry is the effect exerted by a Substituent on modifying Electrostatic forces operating on a nearby These ylids can be generated by condensation of an α-amino acid and an aldehyde or by thermal ring opening reaction of certain N-substituted aziridines. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this An aldehyde is an organic compound containing a terminal Carbonyl group. Aziridines are a group of Organic compounds sharing the aziridine Functional group which is a three membered Heterocycle with one Amine group Stable carbenes also have a ylidic resonance structure e. A persistent carbene (also known as a stable carbene or an Arduengo carbene is a type of Carbene demonstrating particular stability despite also being a Reactive g. :

• Iminophosphoranes (also called:phosphazides) with general structure R₃P⁺-N^-R are intermediates in the Staudinger reduction. The Staudinger reaction or Staudinger reduction is a Chemical reaction in which the combination of an Azide with a Phosphine or Phosphite

• The active form of Tebbe's reagent is often considered a titanium ylide. The Tebbe reagent is (C5H52TiCH2ClAl(CH32 an Organometallic compound used in the methylenation of Carbonyl Like the Wittig reagent, it is able to replace the oxygen atom on carbonyl groups with a methylene group. Compared with the Wittig reagent, it has more functional group tolerance.

Ylide reactions

An important ylide reaction is of course the Wittig reaction but there are more. The Wittig reaction is a Chemical reaction of an Aldehyde or Ketone with a triphenyl phosphonium ylide (often called a Wittig reagent Many ylids are 1,3-dipoles and interact in 1,3-dipolar cycloadditions. For instance an azomethine ylid is a dipole in the Prato reaction with fullerenes. The Prato reaction in Fullerene chemistry describes the functionalization of Fullerenes and Nanotubes with Azomethine ylides in a 13-dipolar "C60" and "C-60" redirect here For other uses see C60 (disambiguation.

Many ylids also react as olefins in rearrangement reactions such as a [3,3]-sigmatropic reaction observed in certain phosphonium ylids ^{[1] [2]}

Wittig reagents are found to react as nucleophiles in SN₂' substitution:^[3]

The initial addition reaction is followed by an elimination reaction. A rearrangement reaction is a broad class of Organic reactions where the carbon skeleton of a Molecule is rearranged to give a Structural isomer of the original A Sigmatropic reaction in Organic chemistry is a Pericyclic reaction wherein the net result is one Sigma bond changed to another sigma bond. An allylic rearrangement or allylic shift is an Organic reaction in which the Double bond in an Allyl chemical compound shifts to the next carbon An elimination reaction is a type of Organic reaction in which two Substituents are removed from a molecule in either a one or two-step mechanism.

References

1. ^ Ferguson, Marcelle L. ; Senecal, Todd D. ; Groendyke, Todd M. ; Mapp, Anna K. (2006). "[3,3]-Rearrangements of Phosphonium Ylides". J. Am. Chem. Soc. 128 (14): 4576–4577. The Journal of the American Chemical Society (usually abbreviated as J doi:10.1021/ja058746q. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
2. ^ (i) Reaction of allyl alcohol with 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane forms a phosphite ester. Allyl alcohol or 2-propen-1-ol is an Organic compound with the formula CH2=CHCH2OH A phosphite ester or organophosphite is a type of Chemical compound with the general structure P(OR3 (ii) Metal carbene addition (from ethyl diazoacetate and ClFeTPP) forms an ylid. A transition metal carbene complex in Organometallic chemistry is a compound bearing a formal carbon-metal bond. Diazo refers to a type of Organic compound that has two linked nitrogen (azo compounds A porphyrin is a heterocyclic Macrocycle derived from four Pyrroline subunits interconnected via their α carbon atoms via Methine bridges (=CH- (iii) A rearrangement reaction (in blue) yields a phosphonate. Phosphonates or Phosphonic acids are organic compounds containing one or more C-PO(OH2 or C-PO(OR2 (with R= Alkyl, Aryl) groups
3. ^ Ramesh M. Patel and Narshinha P. Argade (2007). "Facile SN2' Coupling Reactions of Wittig Reagents with Dimethyl Bromomethylfumarate: Synthesis of Enes, Dienes, and Related Natural Products". J. Org. Chem. 72 (13): 4900 - 4904. The Journal of Organic Chemistry (abbreviated as J Org Chem or JOC) is a Scientific journal for original contributions of fundamental doi:10.1021/jo070728z. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  

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