A residue from heat treatment and distillation of petroleum fractions. It is solid
at room temperature, consists of a complex mixture of numerous predominantly aromatic
and alkyl-substituted aromatic
hydrocarbons, and exhibits a broad softening range instead of a defined
melting temperature.
Note:
The hydrogen
aromaticity (ratio of aromatic to total hydrogen atoms) varies between 0.3 and 0.6. The aliphatic
hydrogen atoms are typically present in
alkyl groups substituted on aromatic rings or as naphthenic hydrogen.
Source:
PAC, 1995, 67, 473
(Recommended terminology for the description of carbon as a solid (IUPAC Recommendations
1995))
on page 499