A
special kind of multiple bonding, which we will learn later is vital
in energy-trapping molecules such as chlorophyll, is illustrated by
benzene,C6H6;. As indicated on the
right, the six carbon atoms in benzene are linked into a hexagon,
with each carbon atom bonded to two other carbon atoms and one hydrogen
atom. This leaves each of the six carbon atoms with one additional
electron, and these six electrons are the raw materials for three
more electron-pair bonds. One way of picturing these bonds would be
an alternation of single bonds and double bonds around the hexagon,
as shown in the right. This would imply an alternation of long and
short C-C bonds around the ring, yet every physical measurement that
we can carry out on benzene suggests that all of the C-C bonds are
alike.