Examples of alkyne in the following topics:
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- Diborane reacts readily with alkynes, but the formation of substituted alkene products leaves open the possibility of a second addition reaction.
- Because of the alkyl branching, only two alkenes add to a BH3 moiety (steric hindrance again), leaving one B-H covalent bond available for reaction with an alkyne, as shown below.
- An important application of disiamylborane is its addition reaction to terminal alkynes.
- Hydroboration of internal alkynes is not a particularly useful procedure because a mixture of products will often be obtained, unless the triple-bond is symmetrically substituted.
- Reactions of alkynes with oxidizing agents such as potassium permanganate and ozone usually result in cleavage of the triple-bond to give carboxylic acid products.
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- Reactions with alkynes are more sensitive to solvent changes and catalytic influences than are equivalent alkenes.
- Why are the reactions of alkynes with electrophilic reagents more sluggish than the corresponding reactions of alkenes?
- It is possible that vinyl cations stabilized by conjugation with an aryl substituent are intermediates in HX addition to alkynes of the type Ar-C≡C-R, but such intermediates are not formed in all alkyne addition reactions.
- This is illustrated for alkenes versus alkynes by the following energy diagrams.
- Complexes formed by alkenes and alkynes with transition metals are different from the simple pi-complexes noted above.
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- Alkenes and alkynes are more reactive than alkanes due to their pi bonds.
- Cycloaddition processes involving alkynes are often catalyzed by metals.
- Alkenes and alkynes can react with hydrogen halides like HCl and HBr.
- Water can be added across triple bonds in alkynes to yield aldehydes and ketones for terminal and internal alkynes, respectively.
- Give examples of the various reactions that alkenes and alkynes undergo
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- Alkenes and alkynes are named similarly to alkanes, based on the longest chain that contains the double or triple bond.
- Alkenes are hydrocarbons that contain one or more double bonds, while alkynes contain one or more triple bonds.
- Alkene and alkyne compounds are named by identifying the longest carbon chain that contains both carbons of the double or triple bond.
- Next, the position of the double or triple bond is indicated using the position of the carbon in the bond with the lower backbone number, and the suffix for the compound is changed to "-ene" for an alkene and "-yne" for an alkyne.
- Translate between the structure and the name of an alkene or alkyne compound
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- Such a base is sodium amide (NaNH2), discussed above, and its reactions with terminal alkynes may be conducted in liquid ammonia or ether as solvents.
- The acidity of terminal alkynes also plays a role in product determination when vicinal (or geminal) dihalides undergo base induced bis-elimination reactions.
- If the very strong base sodium amide is used, the terminal alkyne is trapped as its sodium salt, from which it may be released by mild acid treatment.
- The resulting allenic carbanions undergo rapid proton transfer equilibria, leading to the relatively stable terminal alkyne conjugate base.
- This isomerization may be used to prepare longer chain 1-alkynes, as shown in the following conversion of 3-heptyne to 1-heptyne.
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- Indeed, most of the alkene addition reactions discussed earlier also take place with alkynes, and with similar regio- and stereoselectivity.
- Alkenes and alkynes show a curious difference in behavior toward catalytic hydrogenation.
- Independent studies of hydrogenation rates for each class indicate that alkenes react more rapidly than alkynes.
- Before hydrogen can add to a multiple bond the alkene or alkyne must be adsorbed on the catalyst surface.
- The Lindlar catalyst permits adsorption and reduction of alkynes, but does not absorb alkenes sufficiently to allow their reduction.
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- The sp-hybrid carbon atoms of the triple-bond render alkynes more electrophilic than similarly substituted alkenes.
- As a result, alkynes sometimes undergo addition reactions initiated by bonding to a nucleophile.
- Electron addition to a functional group is by definition a reduction, and we noted earlier that alkynes are reduced by solutions of sodium in liquid ammonia to trans-alkenes.
- Returning to the reducing capability of the blue electron solutions, we can write a plausible mechanism for the reduction of alkynes to trans-alkenes, as shown below.
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- Aliphatic hydrocarbons can be classified based on the structure and bonding of the carbon skeleton into one of three groups: alkanes, alkenes, and alkynes.
- Alkenes and alkynes are known as unsaturated hydrocarbons because some of the carbons are connected to fewer than four neighboring atoms.
- Alkenes contain at least one double bond, while alkynes contain at least one triple bond.
- For example, a chemical structure can be both aromatic and contain an alkyne.
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- As with alkenes, the addition of water to alkynes requires a strong acid, usually sulfuric acid, and is facilitated by mercuric sulfate.
- However, unlike the additions to double bonds which give alcohol products, addition of water to alkynes gives ketone products ( except for acetylene which yields acetaldehyde ).
- The initial product from the addition of water to an alkyne is an enol (a compound having a hydroxyl substituent attached to a double-bond), and this immediately rearranges to the more stable keto tautomer.
- For terminal alkynes the addition of water follows the Markovnikov rule, as in the second example below, and the final product ia a methyl ketone ( except for acetylene, shown in the first example ).
- For internal alkynes ( the triple-bond is within a longer chain ) the addition of water is not regioselective.
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- Reversible loss of CO ligands frees coordination sites and facilitates the oxidative addition of alkenes or alkynes.
- However, metallocyclobutenes derived from alkyne reactants undergo electrocyclic ring opening to a new alkylidene species.
- The unsaturated carbene supplies three carbon atoms and a carbon monoxide unit to the product phenol, and the alkyne reactant provides the remaining carbons.