Editing Alkyne (section)

===Terminal and internal alkynes===
Internal alkynes feature carbon substituents on each acetylenic carbon. Symmetrical examples include [[diphenylacetylene]] and [[3-hexyne]]. They may also be asymmetrical, such as in [[2-pentyne]].

Terminal alkynes have the formula {{chem2|RC≡CH}}, where at least one end of the alkyne is a hydrogen atom. An example is [[methylacetylene]] (propyne using IUPAC nomenclature).  They are often prepared by alkylation of [[monosodium acetylide]].<ref>{{cite journal |doi=10.15227/orgsyn.030.0015 |title=''n''-Butylacetylene |journal=Organic Syntheses |date=1950 |volume=30 |page=15|author=K. N. Campbell, B. K. Campbell }}</ref> Terminal alkynes, like [[acetylene]] itself, are mildly acidic, with p''K''<sub>a</sub> values of around 25. They are far more acidic than alkenes and alkanes, which have p''K''<sub>a</sub> values of around 40 and 50, respectively. The acidic hydrogen on terminal alkynes can be replaced by a variety of groups resulting in halo-, silyl-, and alkoxoalkynes. The [[carbanion]]s generated by deprotonation of terminal alkynes are called [[acetylide]]s.<ref name="de57">{{cite book|last=Bloch|first=Daniel R.|title=Organic Chemistry Demystified|year=2012|publisher=McGraw-Hill|isbn=978-0-07-176797-2|pages=57|edition=2nd}}</ref> Internal alkynes are also considerably more acidic than alkenes and alkanes, though not nearly as acidic as terminal alkynes.  The C–H bonds at the α position of alkynes (propargylic C–H bonds) can also be deprotonated using strong bases, with an estimated p''K''<sub>a</sub> of 35.  This acidity can be used to isomerize internal alkynes to terminal alkynes using the [[alkyne zipper reaction]].