Related Experiment Video
Updated: Apr 18, 2026
Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Dimerization of two alkyne units: model studies, intermediate trapping experiments, and kinetic studies
Sven Fabig1, Gebhard Haberhauer, Rolf Gleiter
1Institut für Organische Chemie, Universität Duisburg-Essen , Universitätsstrasse 7, D-45117 Essen, Germany.
Substituents on alkynes influence their dimerization into diradicals and dicarbenes. Electron-withdrawing groups lower activation energy, enabling synthetic routes to cyclohexadiene derivatives.
Area of Science:
- Quantum Chemistry
- Organic Chemistry
- Computational Chemistry
Background:
- Alkyne dimerization is a key reaction in organic synthesis.
- Understanding substituent effects on alkyne reactivity is crucial for reaction design.
Purpose of the Study:
- Investigate the dimerization of substituted alkynes.
- Determine the influence of various substituents on reaction pathways and energetics.
- Explore potential synthetic applications.
Main Methods:
- High-level quantum chemical calculations (B2PLYPD and CCSD(T)).
- Analysis of diradical and dicarbene intermediates.
- Comparison with experimental trapping and kinetic studies.
Main Results:
- Monosubstituted alkynes favor bond formation at the unsubstituted carbon.
- Electronegative substituents (e.g., F, Cl) decrease activation and reaction energies.
- Strong π-donors (e.g., NH2, OH) facilitate dicarbene formation.
- Phenylacetylene reactivity follows the order: F > OCH3 > Cl > H.
- Experimental studies confirm computational predictions.
Conclusions:
- Substituent effects, particularly electronegativity and π-donating ability, significantly impact alkyne dimerization.
- The reaction mechanism involves stabilizing hyperconjugative interactions.
- Substituted phenylacetylenes offer a promising synthetic route to cyclohexadiene derivatives.
More Related Videos
Related Concept Videos
02:27Preparation of Alkynes: Alkylation Reaction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
02:38Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:37Structure and Physical Properties of Alkynes
In nature, compounds containing both carbon and hydrogen are known as "hydrocarbons". Aliphatic hydrocarbons are compounds whose molecules contain saturated single bonds (i.e., alkanes) or unsaturated double or triple bonds. Alkenes contain carbon–carbon double bonds and have a structural formula CnH2n. Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented by the formula CnH2n-2.
The...
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration