Just like C=C double bonds, C≡C triple bonds have a special type of reactivity associated with them, so it’s useful to call a C≡C triple bond a functional group. Alkynes are linear so we Alkynes contain C≡C triple bonds Just like C=C double bonds, C≡C triple bonds have a special type of reactivity associated with them, so it’s useful to call a C≡C triple bond a functional group. Alkynes are linear so we draw them with four carbon atoms in a straight line. Alkynes are not as widespread in nature as alkenes, but one fascinating class of compounds containing C≡C triple bonds is a group of antitumour agents discovered during the 1980s. Calicheamicin is a member of this group. The high reactivity of this combination of functional groups enables calicheam icing to attack DNA and prevent cancer cells from proliferating. For the fi rst time we have drawn a molecule in three dimensions, with two bonds crossing one another—can you see the shape?