Chemistry
Organic Building Blocks
Alkynyls
Alkynes are unsaturated hydrocarbons that possess at least one carbon–carbon triple bond. The homologous series of the simplest acyclic alkynes, which contain only one triple bond and no other functional groups, have the general chemical formula CnH2n−2. As with other hydrocarbons, alkynes tend to be hydrophobic.
Alkynes are rod-like due to the 180° H–C≡C bond angles present in acetylene, which also accounts for the infrequency of cyclic alkynes.
Compared to the C=C bond distance in alkenes (132 pm, for C2H4) or the C-C bond distance in alkanes (153 pm), the C≡C bond distance in acetylene (118 pm) is significantly shorter.
With a total bond strength of 839 kJ/mol, the triple bond is exceptionally robust. The contribution of the sigma bond to this strength is 369 kJ/mol, while the first pi bond and the second pi bond contribute 268 kJ/mol and 202 kJ/mol, respectively.
Acetylene and other terminal alkynes exhibit a mild acidity, with pKa values of approximately 25, surpassing the acidity of alkenes and alkanes with pKa values of approximately 40 and 50, respectively.
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2-Amino-N-(prop-2-yn-1-yl)acetamide hydrochloride
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4-Methylhex-1-yn-3-amine hydrochloride
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Trimethyl(3-((trimethylsilyl)oxy)prop-1-yn-1-yl)silane
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2-Fluoro-4-(trifluoromethyl)phenylacetylene
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1,4-Bis(dodecyloxy)-2,5-diethynylbenzene
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3',5'-Bis(trifluoromethyl)phenylacetylene