| 释义 |
isomeric, a.|aɪsəʊˈmɛrɪk|
[f. as isomer + -ic; in mod.F. isomérique: after Ger. isomerisch (Berzelius, Jahresbericht of Swed. Acad. Sciences, 31 March 1831).]
1. a. Chem. Composed of the same elements in the same proportions, and having the same molecular weight, but forming different substances, with different properties (owing to the different grouping or arrangement of the constituent atoms). Said of two or more compounds, or of one compound in relation to another (const. with).
This was the sense in which the term was introduced by Berzelius; but many later chemists (e.g. Wanklyn in Watts Dict. Chem. 1865) have applied it in a wider sense, so as to include also the polymeric compounds of Berzelius, i.e. those which have their elements in the same proportions, but the number of atoms in one a multiple of those in the other, e.g. butyric acid C4H8O2, and aldehyde C2H4O; by these the isomeric compounds of Berzelius have been distinguished as metameric. More recent authors again (e.g. Tilden in Fownes' Chem. 1886) have used these terms more narrowly, subdividing the isomeric of Berzelius into isomeric strictly so called, and metameric; the former being compounds of the same molecular composition, which exhibit the same or closely similar decompositions and transformations, when subjected to the action of the same re-agents, such as the C10H8 hydrocarbons, the glucoses, the tartaric acids, etc.; the latter, those which exhibit dissimilar transformations under similar circumstances, as propionic acid, methyl acetate, and ethyl formate C3H6O2.
1838T. Thomson Chem. Org. Bodies 605 From the analysis of this substance [benzoin] it appears to be isomeric with the hydret of benzoyl. 1842–3Grove Corr. Phys. Forces (1874) 117 These solutions are what is termed isomeric, that is, have as far as can be discovered, the same chemical constitution. c1865J. Wylde in Circ. Sc. I. 311/2 Isomeric bodies have similar chemical constituents in the same proportions, and yet their external form may differ, as in sugar and starch. 1865–72Watts Dict. Chem. III. 415 Two or more different bodies which are composed of the same elements, and of the same proportions of those elements (i.e. which have the same percentage composition) are said to be isomeric. 1880E. Cleminshaw Wurtz' Atom. The. 294 We may..imagine isomeric compounds to be produced, according to the place occupied by the atoms fixed in the molecule. 1882Gilburt in Jrnl. Quekett Club Ser. ii. i. 27 We have already seen that cellulose, sugar, starch, and inulin, are isomeric with each other. 1892Morley & Muir Watts' Dict. Chem. III. 88/2 According to our modern conceptions, truly isomeric substances..are equi-molecular compounds containing identical radicles arranged in relatively different modes; and..bearing in mind that it was obviously the intention of Berzelius to limit the scope of the expression, the term isomeric should be used only with reference to such compounds.
b. Physics. Of, pertaining to, or designating nuclear isomers; isomeric transition, a radioactive transition from a metastable state to a lower energy state of the same nuclide.
1934Physical Rev. XLV. 729/1 Another consequence of the introduction of negative protons is the possibility of the existence of isomeric nuclei, that is, nuclei with the same charge and mass but different internal structure. 1937Ibid. LI. 1011 The 18 minute, 4·2 hour, and 35 hour activities must all belong to Br80 and Br82, i.e. one of these isotopes appears to exist in two isomeric forms, from which it decays with different periods. 1950Glasstone Sourcebk. Atomic Energy x. 276/1 Over seventy examples of nuclear isomerism have been discovered, and the phenomenon of decay by isomeric transition, that is, by the spontaneous conversion of one nuclear isomer into another, has been elucidated. In most instances there are isomeric pairs only, but triple isomerism has been observed in a few cases. 1955R. D. Evans Atomic Nucleus vi. 231 By the usual definition, an isomeric level is one whose half-period is ‘measurably’ long. 1970Marmier & Sheldon Physics of Nuclei & Particles II. xv. 1276 Those nuclei whose ground-state configuration is modified by the preferential-filling rule would be expected to display low-lying excited states whose configuration corresponds to that of an unmodified ground state; because of the large spin change occasioned by this effect, the excited state is usually an isomeric state.
2. Comp. Anat. Pertaining to or of the nature of an isomere; homologous.
1890Cent. Dict. s.v., Isomeric segments of the limbs.
So isoˈmerical a. = isomeric; isoˈmerically adv.
In recent Dicts. |