The ratio of aromatic to aliphatic hydrogen depends mainly on the source of the starting
material. The hydrogen
aromaticity (ratio of aromatic to total hydrogen atoms) varies between 0.3 and 0.9. The aliphatic
hydrogen in pitch is largely associated with alkyl side chains substituted on aromatic
rings. The content of
heterocyclic compounds in pitches varies depending on their origins. Also, the softening temperature can
vary in a broad range between about
and
depending on the
molecular weight (
relative molecular mass) and composition of the constituents.