289
Structural Group Analysis
naphthenic and paraffinic carbon only, is an exact measure of the number of rings. As compared
with paraffins, each ring closure involves a reduction by two hydrogen atoms. If R T is the number of
rings of the hypothetical molecule,
R T = 1 + (0.08326 − 0.005793H′)M′
To derive a complete set of carbon distribution and ring content figures from %C A and R T , an
assumption must be made about the type of rings present. It has been assumed that all rings are six
membered and, in the case of the polycyclic materials, are kata-condensed; this type of condensation only occurs in such a way that the rings have two carbon atoms in common, as, for example,
naphthalene, anthracene, or tetracene. However, the occurrence of systems based on anthracene and
tetracene is now considered less likely than that occurrence of system based on phenanthrene and
chrysene in crude oil. The natural product precursors of petroleum (Chapter 3) are considered more
likely to produce the linear condensed aromatic systems.
However, for C R , that is, the average number of ring carbon atoms per molecule, assuming that
only kata-condensed six-membered rings are present,
C R = 4RT + 2R TS
where R TS is the number of substantial rings (R TS = RT if R T < 1 and R TS = 1 if R T > 1). In a katacondensed system, it is possible to differentiate between the rings insofar as one ring (a substantial
ring) has six carbon atoms and the additional rings contribute only four carbon atoms each.
Thus, the percentage carbon in ring structures is given by the expression
%C P = 240,200(2R T + R TS )/M(100 − H)
The carbon distribution is
%C P = 100 − %C R
%C N = %C R − %C A
where
C N is naphthene carbon
C A is aromatic carbon
Furthermore, since
%C A = 240,200(2R A + R AS )/M(100 − H)
where R AS is the number of substantial aromatic rings (R AS = R A if R A < 1 and R AS = 1 if R A > 1),
then for R A < 1,
R A = %C A M(100 − H)/720,600
For R A > 1,
R A = [%C A M(100 − H)/480,400] − 0.5
The naphthene ring content is deduced from the relationship
R N = R T − R A
Structural Group Analysis
naphthenic and paraffinic carbon only, is an exact measure of the number of rings. As compared
with paraffins, each ring closure involves a reduction by two hydrogen atoms. If R T is the number of
rings of the hypothetical molecule,
R T = 1 + (0.08326 − 0.005793H′)M′
To derive a complete set of carbon distribution and ring content figures from %C A and R T , an
assumption must be made about the type of rings present. It has been assumed that all rings are six
membered and, in the case of the polycyclic materials, are kata-condensed; this type of condensation only occurs in such a way that the rings have two carbon atoms in common, as, for example,
naphthalene, anthracene, or tetracene. However, the occurrence of systems based on anthracene and
tetracene is now considered less likely than that occurrence of system based on phenanthrene and
chrysene in crude oil. The natural product precursors of petroleum (Chapter 3) are considered more
likely to produce the linear condensed aromatic systems.
However, for C R , that is, the average number of ring carbon atoms per molecule, assuming that
only kata-condensed six-membered rings are present,
C R = 4RT + 2R TS
where R TS is the number of substantial rings (R TS = RT if R T < 1 and R TS = 1 if R T > 1). In a katacondensed system, it is possible to differentiate between the rings insofar as one ring (a substantial
ring) has six carbon atoms and the additional rings contribute only four carbon atoms each.
Thus, the percentage carbon in ring structures is given by the expression
%C P = 240,200(2R T + R TS )/M(100 − H)
The carbon distribution is
%C P = 100 − %C R
%C N = %C R − %C A
where
C N is naphthene carbon
C A is aromatic carbon
Furthermore, since
%C A = 240,200(2R A + R AS )/M(100 − H)
where R AS is the number of substantial aromatic rings (R AS = R A if R A < 1 and R AS = 1 if R A > 1),
then for R A < 1,
R A = %C A M(100 − H)/720,600
For R A > 1,
R A = [%C A M(100 − H)/480,400] − 0.5
The naphthene ring content is deduced from the relationship
R N = R T − R A