A second set of constitutional isomers with the formula C 8 H 14 O was constructed for molecules bearing a C=O (oxo-group) and C=C (alkene-group) on an octane backbone. These isomers are thus formed by the following substance classes: one ketene, one conjugated aldehyde, four conjugated ketones, five nonconjugated aldehydes and eight non-conjugated ketones (see Fig. ). While these structures are chemically quite different, their orbital symmetries are largely similar, leading to a correlation between their polarizability and HOMO-LUMO gap. Notice, however, that the polarizabilities of the structures are all within 4 % of each other, whereas the variation of HOMO-LUMO gap is about five times larger. As such, the statement that polarizability is mainly determined by the atomic composition and HOMO-LUMO gap by the chemical composition seems to hold, even though some correlation between these two quantities is observed due to the similarity of the structures.