It is now appreciated that, rather than an alteration of single and
double bonds, all the carbon-carbon bonds in benzene are equivalent
and are sort of intermediate between single and double bonds in
strength. The shared electrons are best described as existing in molec-
ular orbitals that encompass the entire ring structure. To represent
this, the structural diagram for benzene is sometimes drawn witha
circle inside the hexagon of carbons. While benzene itself does not
occur in living organisms (it is a highly toxic and combustible liquid),
the ring structure of benzene does occur widely as part of larger struc-
tures of many biological molecules. Let’s look at several of these that
have relevance to the human nervous system.
BenzeneHere are two famous molecules found in the brain, the neurotrans-
mitters dopamine and serotonin.H H H
H. | A sl | H H \
OL LCL LCL UN, 4 s/ N~y
Cc *C Cc H H | C~°’
Il | en “Oo Cc is
C20 HH “ee “o*{ WH
ae H H~ by “07 bye "
Dopamine | 4
H
Serotonin