In the preceding paper of the present series on “Absorption Spectra and Co-ordination of some Cupric Compounds” observations were recorded of the absorption spectra, in the infra-red, visible and ultra-violet regions, of a series of metallic derivatives of copper, ranging from typical metallic salts, such as the blue aqueous sulphate and nitrate, through the blue-green acetate and its homologues, to the violet, yellow or brown derivatives of various β-diketones. In spite of the wide differences of colour in these compounds, the variations were found to be due to a mere displacement of a single absorption band,
e. g
., from 9600 Å. U. in K
2
CuCl
4
to 6000 Å. U. in [Cu. 4NH
3
SO
4
, and the conclusion was drawn that the cupric ion in
all
these compounds exhibits a fourfold co-ordination, either with the anions of the salt or with molecules of the solvent. In the present paper analogous methods have been applied to the study of the metallic derivatives of benzoylcamphor. The investigation had its origin in a suggested correlation between the phenomena of
dynamic isomerism
in prototropic compounds and of
co-ordination
in their metallic derivatives. The former phenomenon was attributed, on the basis of an extended definition of acids and bases,† to the possibility of separating a proton from two alternative positions in the molecule, giving rise to two isomeric anions, which could be converted into one another through an intermediate multipolar ion,
e. g
., HO.C=C─⇌
-
O─C─C-⇌
-
O─
+ | | | | Enol. Enolic anion.
C─
-
C─⇌O=C─
-
C─⇌O=C─C─ | | | | | | Multipolar ion. Ketonic anion. Ketone.
H
CXXXII.—The ultra-violet absorption spectra of aromatic compounds. Part I. Benzene and certain mono-substituted derivatives