PRESIDENTIAL ADDRESS. 325 
The demonstration that optical activity, or enantiomorphism, of molecular con- 
figuration is associated not only with the presence of an asymmetric quadrivalent 
carbon atom, but also with that of a nitrogen atom attached to five different 
radicles, was the result of an improvement of technique in connection with the 
study of optical activity; previously the resolution into optically active compo- 
nents of a potentially optically active basic substance had been attempted with 
the aid of naturally occurring optically active weak acids of the general type of 
d-tartaric acid. The application of the strong d- and J-bromocamphorsulphonic 
acids and the d- and /-camphorsulphonic acids to such purposes rendered 
possible the isolation of the optically active substances containing no asymmetric 
atom other than one of quinquevalent nitrogen. The resolution of asymmetric 
quaternary ammonium salts of the kind indicated was rapidly followed by the 
preparation of optically active substances in which the enantiomorphism is asso- 
ciated with the presence of an asymmetric sulphur, selenium, tin, phosphorus, or 
silicon atom; compounds of the following constitutions were thus obtained in 
optically active modifications :— 
CTE ssi CE 42 Oy! CH, C.H, CH, 
ee a Seis 74 
N Ss Se - 
Apietmi a: PS Ps 
C,H, CH, cl  CH,.CcO.0H cl CO . C,H, 
I 
C.H H, C,H, CH, 
E Cc 
ate ea 
lle eS 
H, I 0) 
C, CH, 
CH, C,H, 
| 
S0,H . C,H, . CH,. Si. 0. Si. CH,. C,H,. SO,H. 
| | 
C,H, C,H, 
In all this work, and amongst all the varied classes of optically active com- 
pounds prepared, it was in every instance possible to indicate one particular 
quadrivalent or quinquevalent atom in the molecule which is separately attached 
to four or five different atoms or radicles; the enantiomorphism of molecular con- 
figuration may be detected, in fact, by the observation that such an asymmetric 
atom is present. It must, however, be insisted that the observed optical activity 
is the result of the enantiomorphism of the molecular configuration; the asym- 
metry of a particular atom is not to be regarded as the cause of the optical 
activity but merely as a convenient geometrical sign of molecular enantio- 
morphism. In 1874 van ’t Hoff realised that molecular enantiomorphism and 
optical activity might conceivably exist without the presence of an asymmetric 
carbon atom, and suggested that compounds of the type 
@ C 
No:c: 0d 
o7 Na 
should be of this kind. Previously this particular case had escaped realisation 
experimentally, but an example fulfilling similar conditions was described in 
: in this year the d- and J-isomerides of 1-methyleyclohexylidene-4-acctic 
acid, 
CH CH, . CH H 
og ast NEO | 
H/ \cH,.CH,”  \cCO.0H 
were obtained.4 The consideration of the constitution of these substances shows 
4 Perkin, Pope, and Wallach, Z'rans. Chem. Soc., 1909, 95, 1789; Perkin and Pope, 
Trans. Chem. Soc., 1911, 99, 1510. 
