656 
The Philippine Journal of Science 
1921 
against an ethylene molecule with sufficient force so that some 
of the bromine shell electrons momentarily penetrate into one of 
the large empty spaces in the shell of one of the carbon atoms, a. 
Such an addition loosens (by repulsion) the restraints on 
shell a electrons sufficiently so that the other carbon atom, 
h, immediately pulls a pair of the shared electrons beyond the 
boundary of shell a. The result is: 
H H 
( b ) (a) | (a) | ( b ) 
Compound A Br — Br cc C ^ C 
I I 
H H 
H H 
H H 
This compound has never been isolated, so far as the writer 
knows. A large number of exactly analogous unstable inter- 
mediate products, however, have been isolated. Vorlander , 16 who 
found it impossible to explain them on the basis of “affinity 
units,” named them class “A” compounds, and the rearranged 
stable forms, class “B.” These designations will be adopted by 
the writer. 
In this case the “class A” compound is very unstable for 
the reason that when bromine a “lends” a pair of electrons to 
carbon a, a general electron shift (toward the right in the 
formula as shown), away from bromine b and toward carbon 
b, takes place notwithstanding the relatively strong attraction 
which the bromine kernel has for electrons. The strained con- 
dition of electron-free spaces originally on carbon a, is thus 
transferred to bromine atom b. The next step is probably that 
another bromine molecule acts on bromine b, just as bromine a 
did on carbon a; forming a positive bromine ion, 
(b) (c) ( d ) 
Br + oo Br — Br, or [Br — Br — Br]t 
This ion is immediately attracted by the negatively charged 
carbon b, upon which one of its atoms is deposited by a repeti- 
tion of the same type of reaction. The movements involved at 
16 Ann. d. Chem. 341 (1905) 1. 
