Page 15 - A TEXTBOOK OF ORGANIC CHEMISTRY

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ISOMERISM •
establishment of the quadrivalent nature of the carbon atom
accompanying this, were connected the endeavours of Kolbe
to derive the constitution of organic compounds from carbonic
acid (according to Kolbe, CO, C = 6, O0 = 8), by the ex-
change of oxygen for organic radicals (A., 113, 293); see also,
for further details, Kopp's " Entwickelung der Chemie in der
eueren Zeit " (Oldenbourg, Munich, 1873), and E. V. Meyer's
" History of Chemistry " (Macmillan, 1891), Schorlemmer's
" Rise and Development of Organic Chemistry " (Macmillan).
The question of the valency of elements, a point which it is
often difficult to decide in inorganic chemistry, is infinitely
easier of determination in the case of the carbon compounds,
because the carbon atom is quadrivalent towards hydrogen as
well as towards chlorine and oxygen, Since the atom of
hydrogen, as the unit of valency, is univalent, and, further,
since the bivalence of the oxygen atom cannot reasonably be
doubted, the valency of the three " organic " elements hydro-
gen, oxygen, and carbon may be considered as resting upon
a sure basis, as may also the conclusions drawn therefrom,
and this all the more since the most important carbon com-
pounds are made up of those three elements.
The above are the normal valencies of H, O and C, but
oxygen can be quadrivalent in the oxonium salts (Chap.
XLILI, A.), and carbon bi- and tervalent (Chap. LII, B.).

Explanation of Isomerism; Determination of
the Constitution of Organic Compounds

The phenomenon known as isomerism is elucidated to a
great extent by the theory of valency. If two substances
have the same molecular formula, i.e. both contain the same
elements and the same number of atoms of the respective
elements in their molecules, then the obvious conclusion to
be drawn is that in the two molecules the atoms are differently
arranged. The methods adopted in determining the manner
,,
in which the atoms are linked together, or, as it is called, the
determination of the chemical constitution of the compound,
is usually based on the following points: (a) The respective
valencies of the atoms constituting the molecule. A compound

or, as
GH, most have the structural formal ['