<P> Terminal alkynes have the formula RC H. An example is methylacetylene (propyne using IUPAC nomenclature). Terminal alkynes, like acetylene itself, are mildly acidic, with pK values of around 25 . They are far more acidic than alkenes and alkanes, which have pK 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 carbanions generated by deprotonation of terminal alkynes are called acetylides . </P> <P> In systematic chemical nomenclature, alkynes are named with the Greek prefix system without any additional letters . Examples include ethyne or octyne . In parent chains with four or more carbons, it is necessary to say where the triple bond is located . For octyne, one can either write 3 - octyne or oct - 3 - yne when the bond starts at the third carbon . The lowest number possible is given to the triple bond . When no superior functional groups are present, the parent chain must include the triple bond even if it is not the longest possible carbon chain in the molecule . Ethyne is commonly called by its trivial name acetylene . </P> <P> In chemistry, the suffix - yne is used to denote the presence of a triple bond . In organic chemistry, the suffix often follows IUPAC nomenclature . However, inorganic compounds featuring unsaturation in the form of triple bonds may be denoted by substitutive nomenclature with the same methods used with alkynes (i.e. the name of the corresponding saturated compound is modified by replacing the "- ane" ending with "- yne"). "- diyne" is used when there are two triple bonds, and so on . The position of unsaturation is indicated by a numerical locant immediately preceding the "- yne" suffix, or' locants' in the case of multiple triple bonds . Locants are chosen so that the numbers are low as possible . "- yne" is also used as an infix to name substituent groups that are triply bound to the parent compound . </P> <P> Sometimes a number between hyphens is inserted before it to state which atoms the triple bond is between . This suffix arose as a collapsed form of the end of the word "acetylene". The final "- e" disappears if it is followed by another suffix that starts with a vowel . </P>

Alkynes are compounds with at least one triple bond