Alkynes are hydrocarbons that have at least one triple bond between two carbon atoms, with the formula C_nH_2n-2. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 The alkynes are traditionally known as acetylenes or the acetylene series, although the name acetylene is also used to refer specifically to the simplest member of the series, known as ethyne (C₂H₂) using formal IUPAC nomenclature. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization

Contents 1 Chemical properties 2 Structure 3 Terminal and internal alkynes 4 Synthesis 5 Reactions 6 References 7 See also

Chemical properties

Unlike alkanes, and to a lesser extent, alkenes, alkynes are unstable and reactive. Alkanes, also known as Paraffins are Chemical compounds that consist only of the elements Carbon (C and Hydrogen (H (i In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon Terminal alkynes and acetylene are fairly acidic and have pK_a values (25) between that of ammonia (35) and ethanol (16). Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor This acidity is due to the ability for the negative charge in the acetylide conjugate base to be stabilized as a result of the high s character of the sp orbital, in which the electron pair resides. Within the Brønsted - Lowry ( protonic) theory of acids and bases, a conjugate acid is the acid member HX of a pair of two compounds that transform Electrons in an s orbital benefit from closer proximity to the positively charged atom nucleus, and are therefore lower in energy. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J This can also be thought of in terms of electronegativity: electrons in an hybrid orbital with high s character reside closer to the nucleus. " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons -->In Chemistry The closer proximity of the electrons to the nucleus allows an acetylinic carbon to have a greater amount of electronegative character. As a result, a proton is more easily removed from the carbon as electrons flow more willingly to a more electronegative atom.

A terminal alkyne with a strong base such as sodium, sodium amide, n-butyllithium or a Grignard reagent, gives the anion of the terminal alkyne (a metal acetylide):

2 RC≡CH + 2 Na → 2 RC≡CNa + H₂

More generally:

RC≡CH + B → RC≡C⁻ + HB⁺, where B denotes a strong base. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Sodium amide, commonly called sodamide is the Chemical compound with the formula NaNH2 n -Butyllithium (abbreviated BuLi is the most prominent Organolithium reagent. The Grignard reaction, named for the French chemist François Auguste Victor Grignard, is an organometallic Chemical reaction in which Alkyl - An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge

The acetylide anion is synthetically useful because as a strong nucleophile, it can participate in C−C bond forming reactions. In Chemistry, a nucleophile (literally nucleus lover as in nucleus and phile) is a Reagent that forms a Chemical bond to

It is also possible to form copper and silver alkynes, from this group of compounds silver acetylide is an often used example. Silver acetylide is an inorganic chemical compound with the formula Ag2C2 a Metal acetylide.

See also: Metal acetylide

Structure

The carbon atoms in an alkyne bond are sp hybridized: they each have 2 p orbitals and 2 sp hybrid orbitals. A metal acetylide is an Alkyne for which the terminal proton (hydrogen has been replaced by a Metal such as Sodium or an Organolithium. -->In Chemistry In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other -->In Chemistry Overlap of an sp orbital from each atom forms one sp-sp sigma bond. In Chemistry, sigma bonds ( σ bonds) are the strongest type of covalent Chemical bond. Each p orbital on one atom overlaps one on the other atom, forming two pi bonds, giving a total of three bonds. In Chemistry, pi bonds ( π bonds) are covalent Chemical bonds where two lobes of one involved electron orbital overlap two lobes The remaining sp orbital on each atom can form a sigma bond to another atom, for example to hydrogen atoms in the parent compound acetylene. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes The two sp orbitals on an atom are on opposite sides of the atom: in acetylene, the H-C-C bond angles are 180°. Molecular geometry or molecular structure is the three- Dimensional arrangement of the Atoms that constitute a Molecule. Because a total of 6 electrons take part in bonding this triple bond is very strong with a bond strength of 839 kJ/mol. In Chemistry, bond strength is measured between two Atoms joined in a Chemical bond. The sigma bond contributes 369 kJ/mol, the first pi bond contributes 268 kJ/mol and the second pi bond is weak with 202 kJ/mol bond strength. The CC bond distance with 121 picometers is also much less than that of the alkene bond which is 134 pm or the alkane bond with 153 pm. A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon

The simplest alkyne is ethyne (acetylene): H-C≡C-H

Terminal and internal alkynes

Terminal alkynes have a hydrogen atom bonded to at least one of the sp hybridized carbons (those involved in the triple bond. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes An example would be methylacetylene (1-propyne using IUPAC nomenclature). Methylacetylene ( propyne) is an Alkyne with the Chemical formula H 3C≡CH

Internal alkynes have something other than hydrogen attached to the sp hybridized carbons, usually another carbon atom, but could be a heteroatom. A good example is 2-pentyne, in which there is a methyl group on one side of the triple bond and an ethyl group on the other side.

The terminal Hydrogen atom is weakly acidic, and can be removed by a very strong base, to yield a salt. This property can be used as a chemical test to distinguish terminal alkynes from others, or the salt may be used to make larger alkyne molecules. A few drops of diamminesilver(I) hydroxide (Ag(NH3)2+ -OH or Ag(NH3)2OH)) solution are added to samples of a non-terminal alkyne and also a terminal alkyne. No reaction occurs for the non-terminal, but the terminal alkyne forms a characteristic white precipitate. This is the insoluble silver salt of the terminal alkyne: R-C≡CH + Ag(NH3)2+ -OH → R-C≡C- Ag+ + NH4+ + NH3 (R = general alkyl group) Warning: transition metal salts of terminal alkynes (metal; acetylides) can be explosive when dry.

Synthesis

Alkynes are generally prepared by dehydrohalogenation of vicinal alkyl dihalides or the reaction of metal acetylides with primary alkyl halides. Dehydrohalogenation is an Organic chemistry reaction from which an Alkene is obtained from an Alkyl halide. In Chemistry vicinal (from Latin vicinus = neighbour stands for any two Functional groups bonded to two adjacent Carbon atoms A halide is a Binary compound, of which one part is a Halogen Atom and the other part is an element or radical that is less The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane In the Fritsch-Buttenberg-Wiechell rearrangement an alkyne is prepared starting from a vinyl bromide. The Fritsch-Buttenberg-Wiechell rearrangement named for Paul Ernst Moritz Fritsch Wilhelm Paul Buttenberg and Heinrich G A vinyl compound is any Organic compound that contains a vinyl group (also called ethenyl) &minus C[[Hydrogen H]] =CH sub>2

Alkynes can be prepared from aldehydes using the Corey-Fuchs reaction and from aldehydes or ketones by the Seyferth-Gilbert homologation. An aldehyde is an organic compound containing a terminal Carbonyl group. The Corey-Fuchs reaction is a series of Chemical reactions designed to transform an Aldehyde into an Alkyne. 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 The Seyferth-Gilbert homologation is a the Chemical reaction of an Aryl Ketone 1 (or Aldehyde) with dimethyl (diazomethylphosphonate

Reactions

Alkynes are involved in many organic reactions. Organic reactions are Chemical reactions involving Organic compounds The basic Organic chemistry reaction types are Addition reactions Elimination

• electrophilic addition reactions
  • addition of hydrogen to give the alkene or the alkane
  • addition of halogens to give the vinyl halides or alkyl halides
  • addition of hydrogen halides to give the corresponding vinyl halides or alkyl halides
  • Nicholas reaction
  • addition of water to give the carbonyl compound (often through the enol intermediate), for example the hydrolysis of phenylacetylene to acetophenone with sodium tetrachloroaurate in water/methanol (scheme shown below)^[1] or (Ph₃P)AuCH₃ ^[2]:

• Cycloadditions
  • Diels-Alder reaction with 2-pyrone to an aromatic compound after elimination of carbon dioxide
  • Azide alkyne Huisgen cycloaddition to triazoles
  • Bergman cyclization of enediynes to an aromatic compound
  • Alkyne trimerisation to aromatic compounds
  • [2+2+1]cycloaddition of an alkyne, alkene and carbon monoxide in the Pauson–Khand reaction
• Metathesis
  • scrambling of alkynes in alkyne metathesis to new alkyne compounds
  • reaction with alkenes to butadienes in enyne metathesis
• nucleophilic substitution reactions of metal acetylides
  • new carbon-carbon bond formation with alkyl halides
• nucleophilic addition reactions of metal acetylides
  • reaction with carbonyl compounds to an intermediate alkoxide and then to the hydroxyalkyne after acidic workup in the Favorskii reaction. In Organic chemistry, an electrophilic addition reaction is an Addition reaction where in a Chemical compound, a Pi bond is removed by the creation Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon Alkanes, also known as Paraffins are Chemical compounds that consist only of the elements Carbon (C and Hydrogen (H (i Abundance Owing to their high Reactivity, the halogens are found in the environment only in compounds or as Ions Halide ions and oxoanions Hydrogen halides (or hydrohalic acids) are acids resulting from the chemical reaction of Hydrogen with one of the Halogen elements ( Fluorine, A vinyl halide in Chemistry is any Alkene with at least one Halide Substituent bonded directly on one of the unsaturated carbons The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane The Nicholas reaction is an Organic reaction where a Dicobalt octacarbonyl -stabilized Propargylic Cation is reacted with a Nucleophile In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen Enols (also known as alkenols) are Alkenes with a Hydroxyl group affixed to one of the carbon atoms composing the Double bond. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Phenylacetylene is an Alkyne hydrocarbon containing a Phenyl group Acetophenone is the Organic compound with the formula C6H5C(OCH3 A cycloaddition is a Pericyclic Chemical reaction, in which two π bonds are lost and two σ bonds are gained the resulting reaction is a The Diels-Alder reaction is an Organic chemical reaction (specifically a Cycloaddition) between a conjugated Diene and a substituted Alkene, 2-Pyrone ( α-pyrone or pyran-2-one) is an Unsaturated cyclic chemical compound with the molecular formula C5H4O2 Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single The Azide-Alkyne Huisgen Cycloaddition is a 13-dipolar cycloaddition between an Azide and a terminal or internal Alkyne to give a 123-triazole Triazole (Htrz refers to either one of a pair of Isomeric Chemical compounds with Molecular formula C2H3N3 having a five-membered The Bergman cyclization or Bergman reaction or Bergman cycloaromatization is an Organic reaction and more specifically a Rearrangement reaction An alkyne trimerisation reaction is a 2+2+2 cyclization reaction where three Alkyne Molecules react to form a Benzene compound In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. The Pauson–Khand reaction (or PKR or PK-type reaction) is a Chemical reaction described as a Cycloaddition between an Alkyne metathesis is an Organic reaction involving the redistribution of Alkyne Chemical bonds This reaction is closely related to Olefin metathesis Alkyne metathesis is an Organic reaction involving the redistribution of Alkyne Chemical bonds This reaction is closely related to Olefin metathesis An Enyne metathesis is an Organic reaction taking place between an Alkyne and an Alkene with a Metal carbene Catalyst forming a In organic and Inorganic chemistry, nucleophilic substitution is a fundamental class of Substitution reaction in which an "electron rich" A carbon-carbon bond is a Covalent bond between two Carbon Atoms. In Organic chemistry, a nucleophilic addition reaction is an Addition reaction where in a Chemical compound a π bond is removed by the creation A metal acetylide is an Alkyne for which the terminal proton (hydrogen has been replaced by a Metal such as Sodium or an Organolithium. In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen An alkoxide is the Conjugate base of an Alcohol and therefore consists of an organic group bonded to a negatively charged Oxygen atom Propargyl alcohol, or 2-propyn-1-ol is an Organic compound which is a simple Alcohol containing an Alkyne functional group. The Favorskii reaction (not to be confused with the Favorskii rearrangement) named for the Russian chemist Alexei Yevgrafovich Favorskii,
• hydroboration of alkynes with organoboranes to vinylic boranes
  • followed by reduction by oxidation with hydrogen peroxide to the corresponding aldehyde or ketone
• oxidative cleavage with potassium permanganate to the carboxylic acids
• migration of the alkyne along a hydrocarbon chain by treatment with a strong base
• Coupling reaction with other alkynes to di-alkynes in the Cadiot-Chodkiewicz coupling, Glaser coupling and the Eglinton coupling. In Organic chemistry, the hydroboration-oxidation reaction is a two-step organic chemical reaction that converts an Alkene into a neutral Alcohol Organoborane or organoboron compounds are Chemical compounds that are organic derivatives of BH3 for example trialkyl boranes Hydrogen peroxide (H2O2 is a very pale blue liquid which appears colorless in a dilute solution slightly more Viscous than water 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 Potassium permanganate is the Chemical compound K[[manganese Mn]] O 4 Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H A coupling reaction or oxidative coupling in Organic chemistry is a catch-all for a range of reactions in organometallic chemistry where two Hydrocarbon The Cadiot-Chodkiewicz coupling in Organic chemistry is a Coupling reaction between a terminal Alkyne and a Haloalkyne Catalyzed The Cadiot-Chodkiewicz coupling in Organic chemistry is a Coupling reaction between a terminal Alkyne and a Haloalkyne Catalyzed The Cadiot-Chodkiewicz coupling in Organic chemistry is a Coupling reaction between a terminal Alkyne and a Haloalkyne Catalyzed

References

See also

• -yne
• cycloalkyne

In Organic chemistry, a cycloalkyne is a Hydrocarbon, which is the cyclic analog of an Alkyne.

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