On the classification of chemical substances by means of generic radicals / by Alexander Crum Brown.

Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: On the classification of chemical substances by means of generic radicals / by Alexander Crum Brown. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    As <^A}n, cAOJn, C,H30,|^^ ^|.}n ,|^jN,^^ In these we have (NHg)', or jj | N common to the group. The generic reactions are—1st, Replacement of one or both atoms of H in NHg by radicals. 2d, The addition of two monatomic atoms to each NH2, N''' becoming N^. 3d, The replace- ment of N''^ by 0 and (ROJ (by the action of nitrous acid), or what comes to the same thing, the replacement of NH^ by HO. All these affect the radical NH, alone, which is therefore the generic radical. In the same way (NH) is the generic radical of the substances derived from ammonia, by the replacement of two atoms of H. The best way of extending this method of classification generally, is to examine the chemical structure of those bodies which form well-marked genera, and see what group of atoms they have in common, and whether the common group (or radical) is that part of the molecule, in which the reactions characteristic of the genus take place. One very well-marked genus is that of the monobasic acids, which have aldehydes and alcohols corresponding to them (Kolbe's Monocar- bonsauren). As examples, we may take acetic acid, acrylic acid, benzoic acid, and cinnamic acid. The chemical structure of these substances is represented, as far as known, by the following graphic formulae:— ' ® © ©-©-©-©-©=© ^ ^ © © § H j (h) Acetic Acid. Acrylic Acid. Benzoic Acid. Cinnamic Acid. -©=© The part common to all these acids is obviously the monatomic radical (0) and the generic reactions take place within it; the salts are formed by the replacement of the H by metal,—chlorides, bromides, aldehydes, &c., by the replacement of the (HO)', by CI, Br, H, &c.; alcohols from the aldehydes, by the addition of H2 A becoming -©-©-©; amides, by the replacement of (HO)' © by NH2; nitriles, by the replacement of O^'and (HO)' by N'; acetones, from two molecules, by the loss of CO(HO) in one, and the substitution of the radical thus produced for HO in the other. {(CO(HO)}' is, then, the generic radical of these acids. As this radical is of very great importance, it is advisible to indi-