Chemistry · Ch 15 — Hydrocarbons
Alkynes
Alkynes
Alkynes are aliphatic unsaturated hydrocarbons containing at least one carbon-carbon triple bond (C-triple-bond-C). Because a triple bond ties up even more of the carbon's bonding capacity than a double bond does, alkynes carry even fewer hydrogen atoms than the corresponding alkene of the same carbon count; their general molecular formula is CnH2n-2. The very first and simplest alkyne, ethyne (C2H2), is universally known by its older common name, acetylene. Table 15.4 lists the structural formulas, common names and IUPAC names of the lower alkynes: ethyne/acetylene (C2H2), propyne/methyl acetylene (C3H4), and the two isomers of C4H6 -- but-1-yne (ethyl acetylene, a terminal alkyne) and but-2-yne (dimethyl acetylene, an internal alkyne). Just as with alkenes, chains carrying two or three carbon-carbon TRIPLE bonds are given their own family names -- al …
Number of carbons (n), molecular formula, structural formula with common name, IUPAC name: n=2, C2H2, H-C(triple bond)C-H, common name Acetylene, IUPAC name Ethyne. n=3, C3H4, CH3-C(triple bond)CH, common name Methyl acetylene, IUPAC name Propyne. n=4, C4H6, CH3-CH2-C(triple bond)CH, common name Ethyl acetylene, IUPAC name But-1-yne. n=4 (second isomer), C4H6, CH3-C(triple bond)C-CH3, common name Dimethyl acetylene, IUPAC name But-2-yne. This table shows that But-1-yne (a terminal alkyne, with the triple bond at the chain end) and But-2-yne (an internal a …