A Manual of the Chemistry of the Carbon Compounds

THE CA11B0N COMPOUNDS. U
All compounds m which the catbon atoms aie linseed together in
the same manner as in the hydrooarbons of the methane series, form
one large group, which has been called the group of the fatty substances,
because most of the monobasic acids, belonging to it, occur in
vegetable and animal fats; and these acids form a homologous series
which is very complete and has been long known. The most characteristic
property of the members of this group is that they undergo
chemical changes principally by substitution, ie. atoms or groups of
atoms are taken out and displaced by others.
A second group includes those compounds in which two or more
atoms of carbon are linked together with more than one of their
combining units. These bodies possess the characteristic property of
combining directly with hydrogen, chlorine, &a, and thus by addition
are changed into compounds belonging to the first group. This group
is usually called the group of the non-saturated compounds, a term
which, however, would imply that these bodies contained carbon
atoms with free combining units, an assumption which for several
reasons appears improbable.
Besides these two groups there exist other groups of carbon compounds,
"which are richer in carbon than the fatty substances, but,
these comport themselves in most of their chemical metamorphoses
like the latter, and only in a few cases form new compounds by
addition, which, however, always contain less hydrogen than fatty
bodies. This class of compounds is again subdivided into different
groups, the best known of which is that of the aromatic sitbstances,
this name being derived from the fact that many of them are found
in essential oils, balsams, resins, &c. Mo compound belonging to
this group contains less than six atoms of carbon, the most simple
hydrocarbon of the group being bciizenc C8H0, in which of the twentyfour
combining units of carbon, eighteen are taken up by the union
of carbon with carbon, whilst the remaining six are combined with
hydrogen, thus;—
HC—CH
// \
HC CH
HC=CH
This linking of the carbon atoms may fignratively be expressed by
saying that they are joined together in an annular or closed chain,
whilst in the fatty and the non-saturated compounds they form an
open chain.
All hydrocarbons contain an even number of atoms of hydrogen; this
is, 03 it will easily be seen, a consequence of carbon being a tetrad.
From this fact it follows further that the sum of the atoms of monad
and triad elements contained in the molecule of a carbon compound must
also always be an even number.
The observation that by replacing in a hydrocarbon one or more