Nikolai N. Semenov - Nobel Lecture - Nobelprize.org

510 1956 N.N.SEMENOV
main problem in theoretical chemistry - the connection between reactivity
and the structure of the particles entering into the reaction.
For chain processes, the reaction of free radicals with the molecules is
characteristic (the reaction of chain propagation). Such reactions belong to
the simplest because here only one bond is disrupted and one bond is
generated afresh. Therefore, the investigation of these simple reactions offers
the best opportunity for breaking fresh ground in the development of the
theory of reactivity and it can be applied subsequently to other types of
reaction also.
It is one of the main tasks of chemistry to create a possibility of rationally
regulating the rate and direction of a chemical change. Unfortunately,
chemistry and the chemicals industry are in this respect lagging behind radio
technology, electronics, atomic engineering, etc., where technology is based
far more on theoretical anticipation and calculation. The chain reaction theory
shows the first possibilities in this respect also.
That the chain reaction includes the stages of initiation of the chain and its
termination, which are greatly dependent upon the average condition and
upon external influences, opens up the possibility of regulating the rate and
sometimes even the yield of the process. The knowledge of the reaction of
chain propagation often makes it possible to control the process in the desired
direction.
Accordingly, the chain theory provides fresh prospects of perfecting established
industrial processes and others which are new and in the development
stage, and is already to a certain extent being applied; this is particularly true
with polymerization processes.
One of the next tasks is the application of the notion of chain theory to
the development of new technology of direct oxidation processes and hydrocarbon
cracking. I would like further to add that, for practical purposes of
chemical technology, radioactive radiation probably offers very good prospects
where chain reactions are concerned.
Certainly, chemical transformation processes are not limited purely to
radical chain reactions which occur with the help of free radicals; a vast number
develop with the help of quite different labile forms.
I am firmly convinced that it is entirely necessary to extend the research
into the mechanism of various types of chemical reactions. It is hardly possible
to enrich chemical technology to any extent without this knowledge
or even to achieve decisive success in biology.
Naturally, there are considerable obstacles in the way. The chemical pro-