ON THE STEREOCHEMISTRY OF NITROGEN. 169 
The Stereochemistry of Nitrogen. By H. O. Jones, M.A., D.Sc. 
[Ordered by the General Committee to be printed in ewtenso.] 
Tue stereochemistry of nitrogen has, for a number of years, attracted 
considerable attention, which was until recently confined chiefly to the 
isomerism of the tervalent compounds; of late years, however, the quin- 
quevalent compounds have been the subject of an exceptionally large 
number of investigations. The former, with the exception of a few out- 
standing problems, may almost be regarded as a closed chapter, whereas 
the latter is still in a state of rapid change. The phenomena exhibited 
by these compounds are so bewildering in their variety, and apparently so 
difficult to reconcile with one another, that this brief review of the present 
state of our knowledge may be useful in promoting discussion which will 
throw some light on the obscure problems that perplex workers in the 
field. 
The facts brought to light by the work on quinquevalent nitrogen 
compounds considered in conjunction with those observed by Professor 
Pope and his collaborators in sulphur and selenium compounds necessitate 
some slight alteration in the prevalent conception of valency, and have 
at the same time supplied the materials for such a revision of ideas. 
No entirely satisfactory hypothesis as to the nature of valency and 
the forces which act in chemical compounds has hitherto been proposed. 
There is, however, a growing conviction that these forces are electrical in 
their origin and arise in consequence of the electrical structure of the 
atom; if this be so, then these forces are very probably localised along 
certain directions outside the atom. 
However, without making any assumption as to the nature of these 
forces, the existence and stability of chemical compounds almost require 
that they should have a definite spatial configuration such as must be 
assumed in order to account for the phenomena of stereoisomerism, and 
further, that the most symmetrical contiguration possible would probably 
be the most stable. By a definite stable configuration is understood an 
arrangement of atoms or groups around a plurivalent atom in which each 
group, under the action of forces exerted on it by the plurivalent atom 
and by the other groups, oscillates (within limits dependent on tempera- 
ture and other conditions) about an equilibrium position in which it 
would probably be stationary at absolute zero. The lines joining the 
centre of the plurivalent atom to the centres of the various atoms or 
groups in their equilibrium positions may be called the ‘ valency directions.’ 
The equilibrium position for any particular radical attached to a pluri- 
valent atom—carbon, for example—would not be fixed, but would be 
dependent to some extent on the other radicals attached to the same 
atom, since the position taken up is the result of the action of a number 
of forces; hence the valency direction must also be variable to some 
extent. These views were quite clearly expressed by van’t Hoff soon 
aiter the tetrahedral configuration for carbon compounds was proposed. 
The new assumption, which had to be made in the light of recent 
experience, is that during a change of valency, such as that of sulphur 
from quadri- to sexa-valency,' the configuration of the molecule may 
alter and the radicals already present take up entirely new positions. 
1 Pope and Neville, Zvans. Chem Soc., 1902, 81, 1560. 
