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Originally appearing in Volume V06, Page 55 of the 1911 Encyclopedia Britannica.
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OOH _CI3O I OH es-CI I CI 'See also:

CO2H ~lCH CO2H C' CI CO C OH CI 0 Cl2 CO2H Clio C~ C12 Cl2 c12 CCl2 See also:CH3 (I) (a) (3) (4) (5) (6) See also:Resorcin (1.3 or See also:meta dioxybenzene) (1) is decomposed in a somewhat similar manner. Chlorination in glacial acetic See also:acid See also:solution yields pentachlor-m-diketo-R-hexene (2) and, at a later See also:stage, heptachlor-m-diketo-R-hexene (3). These compounds are both decomposed by See also:water, the former giving dichloraceto-trichlorcrotonic acid (4), which on boiling with water gives dichlormethylvinyl-a-diketone (5). The heptachlor See also:compound when treated with See also:chlorine water gives trichloraceto-pentachlorbutyric acid (6), which is hydrolysed by alkalis to See also:chloroform and pentachlorglutaric acid (7), and is converted by boiling water into tetrachlor-diketo-R-pentene (8). This latter compound may be chlorinated to perchloracetoacrylic chloride (9), from which the corresponding acid (to) is obtained by treatment with water; alkalis hydrolyse the acid to chloroform and dichlormaleic acid (II). 4 Co-CC12~ CIOC•CCI:CCI•CO•CC13&— ( CO (8) 1 (9) Ccl=ccl~ HO2C•CCl:CC!.CO•CC13- ---•• H02C•CC1:CC1•CO2H+CHCI3 fro) (II) Hydroquinone (1.4 or See also:para-dioxybenzene) (I) gives with chlorine, first, a tetrachlorquinone (2), and then hexachlor-p-diketo-R-hexene (3), which alcoholic potash converts into perchloracroylacrylic acid (4). This substance, and also the preceding compound, is converted by aqueous See also:caustic soda into dichlormaleic acid, trichlorethylene, and hydrochloric acid (5) (Th. Zincke and O. See also:Fuchs, See also:Ann., 1892, 267, p. 1). OH O CI CI CI •--. ci Qjci ~Ct OH O O (I)- (a) (3) (4) (5) Phloroglucin (I.3.5-trioxybenzene) (1) behaves similarly to resorcin, hexachlor [1.3.5] triketo-R-hexylene (2) being first formed. This compound is converted by chlorine water into octachloracetylacetone (3) ; by methyl See also:alcohol into the ester of dichlormalonic acid and tetrachloracetone (4) ; whilst See also:ammonia gives dichloracetamide (5) (Th.

Zincke and O. Kegel, Ber., 189o, 23, p. 1706). OH 0 (3) C13C•CO•CCIZCO•CCI3+See also:

CO2 ct2( `cl2~r (4) C12HC•CO•CHCl2+CH302C•CCVO4CH3 "''(5) Cl2HC•CONH2(I) (a) C(3) (4) (5) The reduction of o-oxybenzoic acids by See also:sodium in amyl alcohol solution has been studied by A. See also:Einhorn and J. S. See also:Lumsden (Ann., 1895, 286, p. 257). It is probable that tetrahydro acids are first formed, which suffer rearrangement to orthoketone carboxylic acids. These substances absorb water and become pimelic acids. Thus salicylic acid yields n-pimelic acid, HOOC•(See also:CH2),.COOH, while o-, m-, and p-cresotinic acids, CsH3(CH3)(OH)(000H), yield isomeric methylpimelic acids. Resorcin on reduction gives dihydroresorcin, which G.

Merling (Ann., 1894, 278, p. 20) showed to be converted into n-glutaric acid, HOOC•(CH2)3•COOH, when oxidized with See also:

potassium permanganate; according to D. Vorlander (Ber., 1895, 28, p. 2348) it is converted into 7-acetobutyric acid, See also:CH3CO•(CH2)3•000H, when heated with baryta to 150-16o°. Configuration of the See also:Benzene Complex.—The development of the " structure theory " in about 186o. brought in its See also:train an appreciation of the chemical structure of the derivatives of benzene. The See also:pioneer in this See also:field was See also:August See also:Kekule, who, in 1865 (Ann., 137, p. 129; see also his Lehrbuch der organischen Chemie), submitted his well-known See also:formula for benzene, so See also:founding the " benzene theory " and opening up a problem which, notwithstanding the immense amount of labour since bestowed upon it, still remains imperfectly solved. Arguing from the existence of only one mono-substitution derivative, and of three di-derivatives (statements of which the rigorous See also:proof was then wanting), he was led to arrange the six See also:carbon atoms in a See also:ring, attaching a See also:hydrogen See also:atom to each carbon atom; being See also:left with the See also:fourth carbon valencies, he mutually saturated these in pairs, thus obtaining the See also:symbol I (see below). The value of this ringed structure was readily perceived, but objections were raised with respect to Kekule's disposal of the fourth valencies. In 1866 See also:Sir See also:James See also:Dewar proposed an unsymmetrical See also:form (II); while in 1867, A. Claus (Theoretische Betrachtungen and deren A nwendung zur Systematik der organischen Chemie) proposed his See also:diagonal formula (III), and two years later, A. Ladenburg (Ber., 2, p.

140) devised his See also:

prism formula (IV), the six carbon atoms being placed at the six corners of a right equilateral triangular prism, with its See also:plane projections (V, VI). CH CH CH HC CH HC CH HC CH HC CH HC CH HC C~CH HC CH HC CH HCCH HC CH HC CH HC t^P,0` cH CH CH i Kekui 12 Dewar inClaus CH Ladenburg One of the earliest and strongest objections urged against Kekul6's formula was that it demanded two isomeric ortho-di-substitution derivatives; for if we number the carbon atoms in cyclical See also:order from i to 6, then the derivatives 1.2 and 1.6 should Objections be different.' Ladenburg submitted that if the 1.2 and toKekule's i.6 compounds were identical, then we should expect the formula. two well-known crotonic acids, CH2.CH: CH•COOH and CH2: CH•CH2•000H, to be identical. This view was opposed by See also:Victor See also:Meyer and Kekule. The former pointed out that the supposed See also:isomerism was not due to an arrangement of atoms, but to the disposition of a See also:valency, and therefore it was doubtful whether such a subtle See also:condition could exert any See also:influence on the properties of the substance. Kekule answered Ladenburg by formulating a dynamic See also:interpretation of valency. He assumed that if we have one atom It is now established that ortho compounds do exist in isomeric forms, instances being provided by chlor-, brom-, and amino-See also:toluene, chlorphenol, and chloraniline; but arguments, e.g. E. Knoevenagel's theory of " motoisomerism," have been brought forward to cause these facts to support Kekule.

End of Article: OOH

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