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C6H5

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Originally appearing in Volume V25, Page 895 of the 1911 Encyclopedia Britannica.
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C6H5 .CH7 H. These facts may be explained in the same way as with See also:

carbon, by admitting See also:tetrahedral grouping. A See also:special feature, however, wanting with carbon, is that compounds with one See also:atom only of the See also:element in question have been obtained as See also:antipodes. A second observation of some See also:interest is that the compounds in question are electrolytes and that, as in solutions, where they are split up into ions, activity must be due to the last, the ionic complex, for in-stance, R1R2R3S, must cause See also:optical rotation. Optical antipodes have also been obtained with quinquevalent See also:nitrogen in compounds of the type: RiRIR3RaNR6. Le See also:Bel observed these in methylethylpropyl-isobutylammonium chloride; since then See also:Pope and Peachey and Wedekind studied the same question more thoroughly, and as a See also:general result it is now stated that ammonium compounds with four different radicals behave as See also:asymmetric carbon compounds. The explanation may be that the four radicals arrange themselves in the two possible tetrahedral configurations, and that the fifth element or See also:group, e.g. See also:chlorine or hydroxyl, more loosely linked, finds its fittest See also:place, as shown in See also:figs. 7 and 8. 2. Stereo-isomers Without Optical Activity.—The See also:chief cases here belong to the derivatives of nitrogen with See also:double linking and the metallic compounds which have been chiefly studied by See also:Werner. The nitrogen compounds showing stereo-See also:isomerism belong to two classes, according to the structural formulae, containing C:N or N :N ; in their general behaviour they seem related to the See also:ethylene derivatives. The first group was detected by See also:Victor See also:Meyer and See also:Goldschmidt in C6H6•C :NOH benzildioxime: CsHs• :NOH.

Later investigations, especially by Hantzsch, showed that a grouping R1•C •R2 R1•C•R2 X•N N X gives rise to stereo-isomerism, the supposed difference being that X is either more See also:

close to R, or to See also:R2. This peculiarity is observed in the aldoximes and ketoximes, derived from See also:aldehydes and See also:ketones on treatment with See also:hydroxylamine, and the two simplest examples are See also:ethyl-aldoxime H3C•CH:NOH, and phenyl-benzyl-ketoxime, (C6H5) (C6H4CH2) C : NOH. As the behaviour of these stereo-isomers much resembles that of ethylene-compounds, they are often indicated as cis- and trans-forms. The second stereo-isomerism in nitrogen-compounds was detected by Schraube in See also:potassium benzenediazotate, and may perhaps be reproduced by the following symbols: C6Hs•N and C6H6N KON NOK. The last group of stereo-isomers, in which insight is most difficult yet, is that of Werner's complex metallic compounds, observed with See also:cobalt, See also:platinum and See also:chromium. No enantiomorphous See also:character throws See also:light here, and there is no relation to ethylene derivatives. With cobalt the fact is that in the hexammonic cobalt salts, e.g. Co(NH3)sC13, when NH3C1 is substituted by NO2 isomerism appears as soon as the number of substituents is two ; Jorgensen's flavo-salts Co(NHa)a(NO2)2C1, and See also:Gibbs's isomeric croceo-salts offer examples. Werner puts forward that a grouping of (NH3)6 at the summits of a See also:regular See also:octahedron around Co may explain this. See also:I00 48 14 o•8 42, Platinum compounds such as (H3N)i PtCl2 have been obtained in fig. 2) this point is seen simply, together with a number of other points which together See also:form the so-called " horopter." According to Joh. See also:Muller, See also:Helmholtz, Hering, Volkmann and others, these are those points of the See also:object-space (e.g.

Q and R in fig. 2), whose images fall on identical or corresponding spots on the retina, by which are meant those points on the retina whose See also:

nerve filaments are See also:united and which are equidistant in the same direction from the centre of the yellow spot (see See also:EYE; See also:VISION). The horopter varies according to the position of the fixed spot in the object-space; for example, it is the ground two forms, Werner admitting here the following See also:plane configurations ClPtz Cl Cl NH3 > and )Pt( See also:HEN/ \NH3 H3N/ Cl shows a behaviour analogous to that of cobalt, and analogous space-formulae may be used here. But, in a general way, at See also:present it is extremely difficult to decide upon their value. (See also:annual since 1904). (J.

End of Article: C6H5

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