• WordNet 3.6
    • n isomerism the state of being an isomer; the complex of chemical and physical phenomena characteristic of isomers
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Webster's Revised Unabridged Dictionary
    • n Isomerism (Chem) The state, quality, or relation, of two or more isomeric substances.
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Century Dictionary and Cyclopedia
    • n isomerism In chem., identity or close similarity of composition and molecular weight, with difference of physical or of both chemical and physical properties. There are three different cases of isomerism: first, where compound bodies have the same ultimate composition and the same molecular weight, but differ in physical properties and in their behavior toward the same reagents, being essentially distinct substances; second, where compounds have the same composition, the same molecular weight, and the same general reactions, but differ in certain physical or chemical properties; third, where compounds differ solely in certain physical properties. The facts of isomerism are generally explained by assuming a difference in the arrangement of the atoms which form the isomeric molecules.
    • n isomerism In the widest sense this term is applied to any two or more chemical compounds having the same percentage composition. Various degrees and kinds of isomerism are distinguished, the primary distinction being between chemical and physical isomerism. Chemical isomerism may be subdivided as follows: Polymerism, which is applied to compounds with the same percentage composition, but with molecular weights differing by some constant value: example, ethylene. C2H4, and butylene, C4H8, molecular weights 28 and 56 respectively. Polymerism may be either accidental or generic, according to whether the compounds belong to the same or different classes. Metamerism is applied to compounds with the same percentage composition and molecular weight, but containing homologous radicals in the molecule: examples are propylamine, C3H7NH2, ethylmethylamine, C2H5NHCH3, and trimethylamine, N(CH3)3. Chain or nucleus isomerism characterizes compounds which have the same number of similar atoms in the molecule, but in which the carbon atoms forming the nucleus are differently grouped: as, normal butane, CH3CH2CH2CH3, and isobutane, (CH3)3CH. Position or place isomerism exists in compounds which have similar nuclei but differ in the relative position of certain substituting atoms or radicals in this nucleus: as, primary or α-propyl chlorid, CH3CH2CH2Cl, and secondary or β-propyl chlorid, CH3CHClCH3. Structural isomerism applies to compounds which have the same percentage composition and molecular weight but differ in the arrangement of atoms in their molecules. Physical isomerism characterizes compounds which consist of varying aggregations of chemically similar molecules. It was first used of substances which are now termed geometrical, stereo-isomeric, or optically isomeric. Alloisomerism is a term occasionally applied to geometrically isomeric compounds one of which can pass into the other by the action of heat Dynamical isomerism is applied to compounds which have perfectly similar linkage and spatial arrangement of atoms, but which differ in energy content, that is. in atomic motion. (Tanatar, Ann. Chem. (Liebig), 273, 55.) Geometrical isomerism or stereo-isomerism marks compounds which have the same constitution, but which differ in the spatial arrangement of certain constituent radicals or atoms. Optical isomerism is applied to stereo-isomeric substances which differ in their action on a ray of polarized light: they either deflect it to the right (dextrorotatory), to the left (levorotatory), or are optically inactive (racemic or mesoform).
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Chambers's Twentieth Century Dictionary
    • n Isomerism ī-som′er-izm the relation between chemical compounds which are identical in their ultimate or percentage composition, but present difficulties in their chemical properties
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Chambers's Twentieth Century Dictionary
Gr. isos, equal, meros, part.


In literature:

It is in such cases that isomerism is observed to occur.
"A History of Science, Volume 4(of 5)" by Henry Smith Williams
To such substances the term Isomeric (from 1/ao1/ equal and aei1/o1/ part) is applied.
"Familiar Letters of Chemistry" by Justus Liebig
The artificial alkaloid paraconine, isomeric with the natural conine, will be referred to later.
"Scientific American Supplement, No. 415, December 15, 1883" by Various
A Bibliography of Geometrical Isomerism.
"Scientific American Supplement, No. 832, December 12, 1891" by Various
Further, the allotropic modifications of elements and the isomerism of compounds increased the difficulties.
"Scientific American Supplement, No. 643, April 28, 1888" by Various
C. in a sealed tube for two hours, it becomes an isomeric compound, boiling at 175 deg.
"Scientific American Supplement, No. 711, August 17, 1889" by Various
More than one hypothesis has been proposed to account for these cases of isomerism, but no one has shown itself to be entirely satisfactory.
"Scientific American Supplement, No. 633, February 18, 1888" by Various
The constitution of the isomeric diazo hydroxides has given rise to much discussion.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 4" by Various
Many substitution derivatives are known: the monosubstitution derivatives being capable of existing in three isomeric forms.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 5" by Various
There are also isomeric quinones of the naphthalene series known as naphthaquinones.
"Coal" by Raphael Meldola
Below the temperatures G and H, isomeric transformation does not occur in measurable time.
"The Phase Rule and Its Applications" by Alexander Findlay
It corresponds to tartaric acid, and, like this substance, it occurs in four stereo-isomeric forms.
"Encyclopaedia Britannica, 11th Edition, Volume 9, Slice 7" by Various
It is therefore isomeric with the hydrocarbon of caoutchouc and with that of oil of turpentine.
"Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 6" by Various
Or how is it that even isomeric compounds may exhibit different qualities?
"A Review of the Systems of Ethics Founded on the Theory of Evolution" by C. M. Williams
A further distinction is necessary to a survey of the subdivisions of isomerism regarded in its widest sense.
"Encyclopaedia Britannica, 11th Edition, Volume 14, Slice 8" by Various
Berzelius cited these acids as examples of compounds which are ISOMERIC.
"Smithsonian Institution - United States National Museum - Bulletin 240" by Anonymous

In news:

Arrestin Translocation Is Stoichiometric to Rhodopsin Isomerization and Accelerated by Phototransduc.
Saccharide Isomerate to Deeply Hydrate Skin and Scalp.
Saccharide Isomerate to Deeply Hydrate Skin and Scalp
Metabolism of Trans and Cis Fatty Acid Positional Isomers Compared to Non-Isomeric Fatty Acids.

In science:

Bk.” These values are the accepted half-lives for the isomeric states.
Discovery of Isotopes of the Transuranium Elements with 93 <= Z <= 98
This value is the currently adopted half-life for the isomeric state.
Discovery of Isotopes of the Transuranium Elements with 93 <= Z <= 98
Three months later Enquist et al. independently reported the observation of the isomeric state which agreed with the value of Morita et al.
Discovery of the astatine, radon, francium, and radium isotopes
In all cases, we can use the relevant map to pull back the counterexample isomerically to ∆t , and we get a counterexample involving t with the same diameter.
The Octagonal PET II: The Topology of the Limit Sets
It decays predominantly to the short-lived isomeric state of 128Sb, which in turn decays to 128Te (shown in the dotted box). (b) The production of 126Sb by νe capture on 128Sn is shown.
Neutrino fluence after r-process freeze-out and abundances of Te isotopes in presolar diamonds
Due to angular momentum selection rules, 126Sb is produced mainly in its isomeric state rather than its high-spin ground state. (c) The production of 126Te through the β -decay of 126Sb is shown.
Neutrino fluence after r-process freeze-out and abundances of Te isotopes in presolar diamonds
The β -decay from the isomeric state dominates the production [see (b)].
Neutrino fluence after r-process freeze-out and abundances of Te isotopes in presolar diamonds
Lett. 84, 6058 (2000). Light-induced reversible isomerizations between two forms having different absorption spectra are referred to photochromism, and the compounds capable of these reactions are called photochromic molecules.
Driven Dynamics: A Probable Photodriven Frenkel-Kontorova Model
E2 decay of the 8+ states that results in the disappearance of isomeric states in 72,74Ni –the corresponding lifetimes move down to the ns region (see Table I).
New T=1 effective interactions for the f5/2 p3/2 p1/2 g9/2 model space; Implications for valence-mirror symmetry and seniority isomers
In addition to gamma-ray lines emitted from deexcitation of daughter nuclei, we considered radioactivity X-ray lines that can be produced from the decay of proton-rich isotopes by orbital electron capture or the decay of isomeric nuclear levels by emission of a conversion electron.
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
We obtained, however, more accurate predictions for isomeric cross sections with TALYS than with EMPIRE-II.
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
However, as the decay scheme of 34Cl was not well known in 1952, it is not clear which fraction of the isomeric state was populated in this experiment.
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
The relevant cross sections for the production of the isomeric pair 58Cog ,m are shown in Figures 9a and b.
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
Isomeric cross section ratios σm/σt were measured for various reaction channels by Sud´ar & Qaim (1996 and references therein).
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
In the absence of data for the isomer formation in α+natFe collisions, we estimated the cross section by multiplying the cross section for the total production of 58Co by the isomeric ratio σm/σt calculated with the TALYS code.
Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity