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 OLEFINE, in organic chemistry, the generic name given to open chain hydrocarbons having only singly and doubly linked pairs of carbon atoms. The word is derived from the French olefiant (from oléfier, to make oil), which was the name given to ethylene, the first member of the series, by the Dutch chemists, J. R. Deiman, Paets van Troostwyk, N. Bondt and A. Lauwerenburgh in 1795. The simple olefines containing one doubly-linked pair of carbon atoms have the general formula ( C𝑛H2𝑛; the di-olefines, containing two doubly-linked pairs, have the general formula C𝑛H2𝑛−2 and are consequently isomeric with the simple acetylenes. Tri-, tetra- and more complicated members are also known. The name of any particular member of the series is derived from that of the corresponding member of the paraffin series by removing the final syllable “-ane,” and replacing it by the syllable “ylene.” Isomerism in the olefine series does not appear until the third member of the series is reached.

The higher olefines are found in the tar which is obtained by distilling bituminous shales, in illuminating gas, and among the products formed by distilling paraffin under pressure (T. E. Thorpe and J. Young, Ann., 1873, 165, p. 1). The olefines may be synthetically prepared by eliminating water from the alcohols of the general formula C𝑛H2𝑛+1·OH, using sulphuric acid or zinc chloride generally as the dehydrating agent, although phosphorus pentoxide, syrupy phosphoric acid and anhydrous oxalic acid may frequently be substituted. In this method of preparation it is found that the secondary alcohols decompose more readily that the primary alcohols of the series, and when sulphuric acid is used, two phases are present in the reaction, the first being the building up of an intermediate sulphuric acid ester, which then decomposes into sulphuric acid and hydrocarbon: C2H5OH→C2H5·HSO4→C2H4+H2SO4. As an alternative to the above method, V. Ipatiew (Ber., 1901, 34, p. 596 et seq.) has shown that the alcohols break up into ethylene's and water when their vapour is passed through a heated tube containing some “contact” substance, such as graphite, kieselguhr, &c. (see also J. B. Senderens, Comptes rendus, 1907, 144, pp. 382, 1109).

In their physical properties, the olefines resemble the normal paraffins, the lower members of the series being inflammable gases, the members from C5 to C14 liquids insoluble in water,

and from C16 upwards of solids. The chief normal members of the series are shown in the table. In chemical properties, however, they differ very markedly from the paraffins. As unsaturated compounds they can combine with two monovalent atoms. Hydrogen is absorbed readily at ordinary temperature in the presence of platinum black, and paraffins are formed; the halogens (chlorine and bromine) combine directly with them, giving dihalogen substituted compounds; the halogen halides to form monohalogen derivatives (hydriodic acid reacts most readily, hydrochloric acid, least); and it is to be noted that the haloid acids attach themselves in such a manner that the halogen atom unites itself to the carbon atom which is in combination with the fewest hydrogen atoms (W. Markownikow, Ann., 1870, 153, p. 256).

OLEG (?–912), prince of Kiev, succeeded Rurik, as being the eldest member of the ducal family, in the principality of Great Novgorod, the first Russian metropolis. Three years later he moved southwards and, after taking Smolensk and other places, fixed his residence at Kiev, which he made his capital. He then proceeded to build a fortress there and gradually compelled the surrounding tribes to pay him tribute, extending his conquests in all directions (883–903) at the expense of the Khazars, who hitherto had held all southern Russia to tribute. In 907,