1.2 Cyclic Systems
1
2
84B3
7~4
3
~
~
31
Cubane: Pentacyclo [4.2.0.0 2 ,5.0 3 ,8.0 4 ,7] octane
On insertion of double bonds, especially more than one such bond, into
such systems one rapidly encounters borderline situations which in many
cases suggest that it might be more reasonable to apply an alternative
naming method. While the following compounds, both valence isomers of
benzene (as is prismane above), can be named clearly and unambiguously
by the von Baeyer system,
Benzvalene
H
HC--C--CH
II , II
HC-~-CH
Dewar benzene
1
' €1:
Tricyclo [2.1.1.0 5 ,6]
hex-2-ene
incorrect
1
60,2
S
3
1
6rA 2
5V3
Tricyclo [3.1.0.0 2 ,6]
hex-3-ene
correct
Bicyclo [2.2.0 ]hexa-2,5-diene
for compounds containing intact benzenoid skeletons the nomenclature of
fused polycycles or of parent structures substituted by side chains is much
more reliable and recommendable.
2
8~3
7~4
Bicyclo[ 4.2.0 ]octa-l,3,5,7tetraene
6
sQJtl1
4 ~
2
2a
better: Cyclobutabenzene