ALKYNE THEORY
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- Germán Fernández
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Alkynes are hydrocarbons that contain carbon-carbon triple bonds. The general molecular formula for acyclic alkynes is CnH2n-2 and its degree of unsaturation is two. Acetylene or ethyne is the simplest alkyne, it was discovered by Berthelot in 1862.
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Rule 1. Alkynes respond to the formula $C_nH_{2n-2}$ and are named by replacing the suffix -ane of the alkane with the same number of carbons by -yne.
![alkyne nomenclature01](/images/stories/organica-i/alkynes/nomenclatura/nomenclatura-alquinos01.png)
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Alkynes have similar physical properties to alkanes and alkenes. They are poorly soluble in water, have a low density and have low boiling points. However, alkynes are more polar due to the greater attraction that an sp carbon exerts on electrons, compared to an sp 3 or sp 2 carbon.
![physical properties of alkynes propiedades físicas de alquinos](/images/stories/organica-i/alkynes/propiedades-fisicas/propiedades-fisicas01.png)
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The carbon-hydrogen bond of terminal alkynes is polarized and shows a slight tendency to ionize.
![alkyne acidity acidez de alquinos](/images/stories/organica-i/alkynes/acidez/acidez-alquinos01.png)
![alkyne acidity acidez de alquinos](/images/stories/organica-i/alkynes/acidez/acidez-alquinos02.png)
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As we saw in the previous point, terminal alkynes have acidic hydrogens that can be removed by strong bases, forming acetylides (conjugate base of the alkyne). Acetylides are good nucleophiles and give mechanisms of nucleophilic substitution with primary substrates.
![alkyne alkylation alquilación de alquinos](/images/stories/organica-i/alkynes/alquilacion/alquilacion-alquinos01.png)
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Alkynes can be prepared by double dehydrohalogenation of vicinal or geminal dihaloalkanes.
![Alkyne synthesis - Double elimination Sintesis alquinos - Doble eliminación](/images/stories/organica-i/alkynes/doble-eliminacion/doble-eliminacion01.png)
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- ALKYNE THEORY
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![hydrogenation-alkynes hidrogenacion-alquinos](/images/stories/organica-i/alkynes/hidrogenacion/hidrogenacion-alquinos01.png)
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- Germán Fernández
- ALKYNE THEORY
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![hydrogenation of alkynes with Lindlar hidrogenación de alquinos con Lindlar](/images/stories/organica-i/alkynes/hidrogenacion-lindlar/hidrogenacion-lindlar01.png)
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- Germán Fernández
- ALKYNE THEORY
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An alternative to hydrogenation with Lindlar's catalyst is the reduction of alkynes with sodium or lithium in liquid ammonia, the difference lies in the alkene obtained. Thus, hydrogenation with Lindlar's catalyst produces cis alkenes, while hydrogenation with sodium in liquid ammonia generates trans alkenes.
![monoelectronic-reduction reduccion-monoelectronica](/images/stories/organica-i/alkynes/reduccion-monoelectronica/reduccion-monoelectronica01.png)
Read more: Hydrogenation of Alkynes with Sodium in Liquid Ammonia
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Alkynes react with aqueous sulfuric acid in the presence of a mercury catalyst to form enols. The enol isomerizes (tautomerizes) rapidly under the reaction conditions to give aldehydes or ketones.
![alkyne hydration hidratación de alquinos](/images/stories/organica-i/alkynes/hidratacion/alquinos-hidratacion01.png)
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Hydroboration is the anti-Markovnikov hydration of an alkyne. A hindered borane (dicyclohexylborane or diisoamylborane) is used as a reagent, obtaining an enol that tautomerizes to aldehyde or ketone. Terminal alkynes give rise to aldehydes, internal ones to ketones.
![hydroboration alkynes01](/images/stories/organica-i/alkynes/hidroboracion/hidroboracion-alquinos01.png)
![hydroboration alkynes01 2](/images/stories/organica-i/alkynes/hidroboracion/hidroboracion-alquinos01-2.png)
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Similar to alkenes, alkynes add hydrogen halides (HBr, HCl, HI) to the triple bond to form alkenyl halides.
![Addition of hydrogen halides to alkynes Adición de haluros de hidrógeno a alquinos](/images/stories/organica-i/alkynes/adicion-haluros-hidrogeno/adicion-haluros-hidrogeno01.png)
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![halogenation of alkynes Halogenación de alquinos](/images/stories/organica-i/alkynes/halogenacion/alquinos-halogenacion01.png)
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![alkyne ozonolysis ozonolisis de alquinos](/images/stories/organica-i/alkynes/ozonolisis/alquinos-ozonolisis01.png)