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Page:Popular Science Monthly Volume 72.djvu/139

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135
COLOR AND CHEMICAL CONSTITUTION


the para-position. Now the activity of these oxygen atoms is to be attributed to the residual affinity which each is known to possess, and hence by the assertion of this affinity when in close proximity to each other, followed quickly by a break in the same, we arrive at the condi- tion known as isorropesis, upon which form of oscillation the color depends. It is necessary in this process that the active groups under- going isorropesis should be adjacent. The pulsations of the benzol ring readily furnish the means by which the two para-atoms are suc- cessively brought under the influence of each other, and hence their positions will approach more nearly to that of adjacent atoms, a point that was confirmed by the similarity in the absorption spectra between para-benzo-quinone and compounds where the two carbonyl groups were actually adjacent. The study of ortho-quinones falls in the same category as the para-quinones and may be explained in a similar manner. Meta-quinones, however, can exist, but momentarily on the hypothesis of the benzol pulsations and hence are unstable.

Isorropesis, as has just been indicated, occurs between adjacent atoms possessing residual affinity. It is also to be remembered that some disturbing force must be brought to bear upon these atoms, for otherwise no make-and-break and consequently no oscillation can take place. In the simplest case studied, that of diacetyl (CH3 — CO — CO — CH3), the disturbing influence rests undoubtedly with the hydrogen atoms of the methyl groups which from their electro-positive nature exert a strong attraction for the electro-negative atoms of oxygen. This constitutes a sort of keto-enol tautomerism, the presence of which should certainly be accounted for in the appearance of the absorption-curve; indeed, the slight extension of the absorption-curve of this compound near the oscillation frequency 3,800 corresponds exactly to the location of a band due to keto-enol tautomerism. The cause of isorropesis in a compound rests, then, upon the disturbances of the residual affinities of the two atoms in juxtaposition. In the examples already cited, those of pyruvic acid and oxalic acid, the hydroxyl group is next to the active carbonyl group. The slight posi- tive nature of the hydrogen atom in this capacity will diminish its disturbing effect upon the second oxygen atom, or that of the carbonyl group, and consequently only the slightest amount of isorropesis will be possible. With the alkyl ester of pyruvic acid the conditions will favor a slight isorropesis, as we have seen, but with oxalic acid there should be none at all. In quinones the residual affinities of the benzol ring constitute the disturbing factors. The hydrogen atoms of the benzol molecule may also exert some disturbance. In general, we may say that the amount of isorropesis must rest upon the disturbing in- fluences which can be brought to bear upon the active groups showing residual affinity, or those susceptible of this new kind of oscillation.

Isorropesis need not always be confined to residual affinities between