had a head near the oscillation frequency 3,700. As the molecule is lighter than that of ethyl aceto-acetate, we should, from previous observations, expect the band to be shifted farther from the red; the opposite, however, is true and the only explanation that seems possible is that the band is the result of a new kind of vibratory motion arising between two carbonyl groups when in close proximity to each other. In order to substantiate these conclusions other derivatives containing two carbonyl groups were studied. But as the carbonyl group in carboxyl has not all the characteristics of a true carbonyl group, attention was turned to the compound diacetyl, CH3 — CO — CO — CH3. Here the absorption band occurs at the oscillation frequency 2,400 (wave-length 4,170 A.U.), which is in the visible blue region of the spectrum, and hence this absorption of colored rays must result in the compound itself taking on the complementary color—that of yellow. In the same way it can be shown that glyoxal, OHC — CHO, gives an absorption band in the visible blue region, and consequently its distinct yellow color may be explained. Oxalic acid, HOOC • COOH, however, with a hydroxyl group next to each carbonyl group and therefore analogous to pyruvic ester, gives no band in the visible spectrum, and is, therefore, colorless.
Upon the theory that a change in linking produces the absorption bands, the only possible explanation would be indicated as follows:
The make-and-break contact between the oxygen atoms would give marked activity to these atoms. Such a process other than tautomerism, where a wandering of a labile atom is suggested, has been named by Stewart and Baly[1] "isorropesis" (equipose), and differs from the former in that the head of its absorption band lies much nearer the red end of the spectrum or almost in the visible violet region. With the diketone known as benzil, C6H5 — CO — CO — C6H5, an absorption band with head at the oscillation frequency 3,900 was noticed in solutions of small concentrations. This would seem to indicate the presence of a certain amount of oscillation due to the benzol nucleus. The residual affinities of the two carbonyl groups are undoubtedly fixed, to some extent, by the free affinities of the benzol molecule, but even so there may be present a small amount of isorropesis between the two carbonyl groups. That such is really the case is demonstrated in solutions of greater concentration by the presence of a very shallow absorption band with head at the oscillation frequency 2,650. Its shallowness, however, argues for only a slight isorropesis; indeed the color of benzil, which is but faintly yellow, may be made to disappear entirely
- ↑ Chem. Soc. Trans., 89, 498, 1906.
