19, 6 Perkins: Addition to the Double Bond, I 655 
because an adequate concept has already been provided, and 
impossible, because usually no minimum attraction point a exists. 
Addition to an already complete shell is possible only when 
the electrons are so displaced from their normal positions as 
to leave large electron-free spaces in the shell. When such 
direct addition occurs, the resulting molecule is unstable, and 
usually ** immediately rearranges so as to reduce the number 
of electrons in the shell to the normal value. 
TWO TYPES OF DIRECT BOND REACTION 
Most of the reactions of organic chemistry involve both addi- 
tion and dissociation. These are divided into two types: 
Type 1.—Direct addition reaction. 
Type 2.—Dissociation-addition reaction. 
In type 1 there is evidence that addition of electrons to a 
Shell, as above defined, takes place before dissociation. In type 
2 there is evidence that dissociation occurs before addition. 
The dissociation is usually, but not always, of the unsymmet- 
rical type. 
REACTIONS OF THE DOUBLE BOND 
As has been intimated, it seems to the writer that the primary 
cause of double bond reactivity is no more or less than was 
Suggested by Baeyer,’® namely, that a double union between 
two atoms cannot exist without a distortion of the binding 
mechanism (the electron shell) of each atom. In fact, some 
so-called “double bonds” exist only in the half dissociated con- 
Pay eae B bietad B). An illustrative case of each 
of the two types of double-bond reaction will be briefly con- 
sidered. 
TYPE 1. DIRECT ADDITION REACTION 
In the case of the addition of bromine to ethylene and similar 
reactions it seems to the writer that various assumptions which 
have been made as to directed valence, tautomerism, opened .up 
force fields, or ionization, are unnecessary to explain the ob- 
served facts. It seems more probable that thermal impacts, aided 
by the slight attraction between the positive and negative areas 
of the respective molecules, occasionally send a bromine molecule 
“Sometimes conditions prevent this rearrangement. Cf. Langmuir’s 
discussion of liquid PCls. Langmuir, I., Journ. Am. Chem. 41 (1919) 
919. 
* Baeyer, A., Ber. deut. chem. Ges. 23 (1890) 1275. 
