Hydrocarbons with one triple bond are referred to as
alkynes. Alkynes have the general formula is C
nH
2n-2 and have four fewer hydrogens than the corresponding alkane which has the general formula C
nH
2n+2.
When deducing the number of alkynes possible for a particular carbon skeleton, it is important again to recognize that some carbons in a given carbon skeleton may be equivalent.
C ≡ C – C – C
C – C ≡ C – C
The carbon skeletons for the two possible C4 alkynes are shown. There can be a triple bond either between the blue and red carbons or between the red carbons.
it is also important to remember that the maximum number of bonds to carbon is four. Therefore each of the triply-bonded carbons may be bonded to a maximum of one other carbon.
This means that there is only one alkyne isomer possible for the carbon skeleton shown at the right, that is with a triple bond between the blue and the orange carbons. The black carbon cannot be involved in a triple bond as it already is bonded to three other carbons.