bicyclo[2.2.1]heptane. The carbon frame of camphor also counts 7 atoms, but is substituted with a carbonyl in this case, hence the suffix heptanone. We start with numbering the carbon frame at the bridgehead atom with the highest priority (methyl goes before proton), hence the bridgehead carbon in front gets number 1, the carbonyl gets number 2 and numbering continues along the carbon chain following the longest path, until the doubly substituted top carbon (number 7). Equal to norbornane, this molecule also has two paths of 2 carbon atoms and one path of 1 carbon atom between the two bridgehead carbons, so the numbers within the brackets stay [2.2.1]. Combining the brackets and suffix (now filling in the position of the carbonyl as well) gives us [2.2.1]heptan-2-one. Besides bicyclo, the prefix should also specify the positions of all methyl substituents so the complete, official name becomes 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one. When naming simple fused bicyclic compounds, the same method as for bridged bicyclic compounds is applied, except the third path between the two bridgehead atoms now consists of zero atoms. Therefore, fused bicyclic compounds have a "0" included in the brackets. For example, decalin is named bicyclo[4.4.0]decane. The numbers are sometimes omitted in unambiguous cases. For example, bicyclo[1.1.0]butane is typically called simply bicyclobutane. The heterocyclic molecule DABCO has a total of 8 atoms in its bridged structure, hence the root name octane. Here the two bridgehead atoms are nitrogen instead of carbon atoms. Therefore, the official name gets the additional prefix 1,4-diaza and the total name becomes 1,4-diazabicyclo[2.2.2]octane. References See also Polycyclic compound Bredt's rule Molecular geometry