o-Oxycarbanil Ethyl Ether. Ketonic form; m. p. 29o.

Thickness of layer of liquid in millimetres.

0.163 gram (1 milligram-mol.) in 100 c.c. alcohol.

0-163 gram (1 milligram-mol.) in 500 c.c. alcohol.

o-Oxycarbanil Ethyl Ether. Enolic form; b. p. 225-230°.

Thickness of layer of liquid in millimetres.

0.163 gram (1 milligram-mol.) in 100 c.c. alcohol.

Thickness

0.163 gram (1 milligram-mol.) in 500 c.c. alcohol.

LXXVIII.-Ultra-violet Absorption Spectra of Some Closed Chain Carbon Compounds. Part II. Dimethylpyrazine, Hexamethylene, and Tetrahydrobenzene.

By WALTER NOEL HARTLEY, F.R.S., and JAMES J. DOBBIE, D.Sc., M.A. IN a former paper (Trans., 1898, 73, 598), we gave the results of the examination of the absorption spectra of thiophen, pyrrole, furfuran, and some of the more important furfuran derivatives. Each of these compounds contains two pairs of carbon atoms doubly linked, the chain being closed by a polyvalent element other than carbon. No trace of selective absorption, such as is shown by benzene, pyridine, and many of their derivatives, could be detected in the spectra of any of these substances.

We have now extended our investigation to 2: 5-dimethylpyrazine,

a substance in which not merely one carbon is replaced by nitrogen in the benzene ring, as in pyridine, but two. It thus belongs to a group not previously examined.

From the analogy between the constitution of this substance and that of pyridine, it was anticipated that it would show a marked selective absorption, and this anticipation proved to be correct. One of the principal reasons for examining a substance of this constitution lay in the fact that whilst pyridine contains the group ⚫C:N once in the benzene structure, dimethylpyrazine contains it twice, and the original formula proposed for cyanuric acid (Trans., 1882, 41, 84) contains it three times; accordingly, if this formula were correct for cyanuric acid and its esters, we should expect that they would exhibit a powerful absorption band, more intense than that of pyrazine, just as that of pyrazine is more intense than that of pyridine. But it has been concluded, from a widely extended experience of the behaviour of such substances under the ultra-violet rays, and particularly from the results of a recent examination of the absorption spectra of its derivatives (Hartley, Proc., 1899, 15, 46), that cyanuric acid does not possess this structure, but one in which

the acid is represented by a ring composed of three H

groups,

a mode of single linking resembling that of a hydropyridine or of a hydroaromatic group with one carbon replaced by nitrogen (Phil.

Trans., Part II, 1885, 519); it should not therefore exhibit selective absorption.

The specimen of dimethylpyrazine used in the experiments was prepared by the reduction of isonitrosoacetone in accordance with the directions given by Gabriel and Pinkus (Ber., 1893, 26, 2206). It boiled constantly at 154-155° (corr.) under atmospheric pressure.

2:5-Dimethylpyrazine.

Curves of Molecular Vibrations.

A layer, 25 mm. thick, of a solution of dimethylpyrazine containing 1 mill.-mol. in 100 c.c. of absolute alcohol cuts off all rays beyond 1/ 2994. On reducing the thickness of the layer to 10 mm., an absorption band makes its appearance, reaching from 1/A 3064 to 1/A 4321. This band is very persistent, and is still traceable in a layer 1 mm. thick of a solution containing 1 mill.-mol. of the

substance dissolved in 500 c.c. alcohol. The band of dimethylpyrazine is thus both wider and also more persistent than that of pyridine. These results are shown in the curve on page 847.

In the paper already referred to, an account was also given of the absorption spectra of diketohexamethylene. Previous investigations had shown that piperidine (Hartley, Trans., 1885, 47, 691) and hexachlorobenzene (Hartley, Trans., 1881, 39, 153) exhibit continuous absorption, but show no absorption band, and, as was to be expected, diketohexamethylene, in which the six carbon atoms are united with each other by a single bond, as in hexachlorobenzene and piperidine, likewise showed no bands in the spectrum.

Through the kindness of Prof. Sydney Young and Miss Fortey, we have recently been enabled to examine a specimen of pure hexamethylene prepared from Galician petroleum. This substance, in comparison with benzene and pyridine, is highly diactinic. A layer, 60 mm. thick, of a solution containing 1 mill.-mol. dissolved in 20 c.c. of alcohol, transmits all rays up to 1/A 3920, whilst a layer of the same solution, 10 mm. thick, transmits practically the whole spectrum. In none of the photographs of the spectra of this substance could any trace of a banded structure be detected.

Professor Young and Miss Fortey were also good enough to place a specimen of pure tetrahydrobenzene in our hands for examination. This substance exhibits somewhat greater general absorption than hexamethylene, a layer, 60 mm. thick, of a solution containing 1 mill.-mol. in 20 c.c. alcohol absorbing all rays beyond 1/A 3694, while absorption is still traceable in a layer of the same solution 1 mm. thick. Like hexamethylene, tetrahydrobenzene shows no selective absorption. The examination of these two substances thus confirms the conclusion previously reached, that the banded spectrum is shown only by substances which possess the true benzenoid structure (Hartley, Trans., 1881, 39, 153).

0.108 gram (1 milligram-mol.) in 100 c.c. alcohol.