Isotopically substituted compounds

As shown by the first prompt there are four types of search, of which we will discuss two exact and substructure (SSS). In an exact search, only information regarding exactly the stracture given will be retrieved, but even so there may well be several answers, because CA treats stereoisomers and isotopically substituted compounds as separate answers. At the conclusion of the search the system gives the number of answers, (e.g., 4). We may now look at the four answers by using the display command. As in the CA File, there is a choice of display formats, but if we choose SUB we will get (1) the Registry Number, (2) the approved CA index name, (3) other names that have appeared in CA for that compound, (4) a structural formula, and (5) the number of CA references since 1967, along with a notation as to... 

A complete analysis of the IR spectra of thienothiophenes 1 and 2 in the gaseous, liquid, and crystalline states was carried out by Kimel feld et a/. The following isotopically substituted compounds were also studied 2-deuterothieno[2,3-h]thiophene (l-2d), 2-deuterothieno[3,2-I)]-thiophene (2-2d), 2,5-dideuterothieno[2,3-h]thiophene (l-2,5-d2), and 2,5-dideuterothieno[3,2-h]thiophene (2-2,5-dj). The IR spectra of oriented polycrystalline films of all compounds were measured in polarized light, and Raman spectra of liquid thienothiophenes 1, l-2d, and 1-2,5-dj, of crystals of thienothiophenes 2 and 2-2,5-d2 and melts of thienothiophenes 2 and 2-2d were analyzed. The planar structure of point-group Cj, for thienothiophene 1 in the liquid and gaseous states was assumed. Then the thirty vibrations of compounds 1 and l-2,5-d2 can be divided into four symmetry classes Aj (11), Bj (10), A2 (4), and B2 (5) the vibrations of molecule (l-2d) (C, symmetry) are divided into two classes A (21) and A" (9). 

An isotopically substituted compound has a composition such that all of the molecules of the compound have only the indicated nuclides at the designated positions. To indicate isotopic substitution in formulas, the nuclide symbols are incorporated into the formulas. To indicate isotopic substitution in spelled-out compound names, the number and symbol (and locants if needed) are placed in parentheses closed up to the name. 

An isotopically labeled compound is a mixture of an isotopically unmodified compound with an analogous isotopically substituted compound or compounds. Isotopically labeled compounds may be specifically labeled or selectively labeled. To indicate isotopic labeling, the number and symbol (and locants if needed) are enclosed in square brackets closed up to the compound name or formula. 

The use of other isotopically labelled compounds may be of great value in the study of unstable intermediates in all cases, however, due allowance should be made for the differing chemical reactivities of the isotopically substituted compounds. 

Note that this distinguishes the specifically labelled compound from the isotopically substituted compound H215NNH2. 

IR-4.4.3.2 Formal treatment as coordination compounds IR-4.4.3.3 Chain compounds IR-4.4.3.4 Generalized salt formulae IR-4.4.3.5 (Formal) addition compounds IR-4.4.4 Figand abbreviations IR-4.5 Isotopically modified compounds IR-4.5.1 General formalism IR-4.5.2 Isotopically substituted compounds IR-4.5.3 Isotopically labelled compounds IR-4.5.3.1 Types of labelling IR-4.5.3.2 Specihcally labelled compounds IR-4.5.3.3 Selectively labelled compounds IR-4.6 Optional modibers of formulae IR-4.6.1 Oxidation state IR-4.6.2 Formulae of radicals IR-4.6.3 Formulae of optically active compounds IR-4.6.4 Indication of excited states IR-4.6.5 Structural descriptors IR-4.7 References... 

IR-4.5.1 General formalism The mass number of any specific nuclide can be indicated in the usual way with a left superscript preceding the appropriate atomic symbol (see Section IR-3.2). When it is necessary to cite different nuclides at the same position in a formula, the nuclide symbols are written in alphabetical order when their atomic symbols are identical the order is that of increasing mass number. Isotopically modified compounds may be classified as isotopically substituted compounds and isotopically labelled compounds. 

IR-4.5.3.1 Types of labelling An isotopically labelled compound may be considered formally as a mixture of an isotopically unmodified compound and one or more analogous isotopically substituted compounds. They may be divided into several different types. Specifically labelled compounds and selectively labelled compounds are treated briefly here and described in more detail in Ref. 5. 

IR-4.5.3.2 Specifically labelled compounds An isotopically labelled compound is called a specifically labelled compound when a unique isotopically substituted compound is added formally to the analogous isotopically unmodified compound. A specifically labelled compound is indicated by enclosing the appropriate nuclide symbol(s) and multiplying subscript (if any) in square brackets. 

Exclusive of special techniques, there exist three general methods for observing isotope effects, each of which was first worked out for the determination of specific reaction rates, or ratios of rates, for classical reactions and only later applied to the study of isotopically substituted compounds. These methods are (1) the Kinetic Method (2) the Method of Competing Reactions and (3) the Method of Product Analysis. Combinations of kinetic and product analysis techniques are also possible. 

Over several years, many LC-MS and LC-MS/MS methods were reported for the simultaneous analysis of trichothecene mycotoxins, including DON and NIV. These methods have been applied to the hygienic craitrol and surveillance of mycotoxins. However, LC-MS requires the use of expensive internal standards such as isotopically substituted compounds. Meanwhile, the precision of LC-UV has been valued, although its sensitivity is lower than that of LC-MS. 

Fig. 1A-F. The 75.5 MHz H-decoupled NMR spectra in aqueous solution at 40°C of the starting isotopically substituted compounds (A, B) and the synthetic products (C-F) obtained from isomerization reactions catalyzed with molybdic acid. D-(2- C)Hamamelose (C) and D-(2- C)sorbose (E) obtained from D-(2- C)fructose (A) D-(l- C)hamamelose (D) and D-(3- C)sorbose (F) obtained from D-(3- C)fructose (B) (Reprinted from Carbohydrate Research, Vol. 319, Zuzana Hricoviniova-Bflikovd, Milos Hricovini, Maria Petrusovd, Anthony S. Serianni, Ladislav Petrus, Stereospecific molybdic acid-catalyzed isomerization of 2-hexul-oses to branched-chain aldoses. Pages 38-46, Copyright 1999, with permission from Elsevier Science.)...

As light stable isotopes with signiflcant relative mass differences (e.g., 2 1 for D and H or 18 16 for oxygen isotopes), there are measmable differences in the physical properties of end member hght stable isotopic compoimds (e g., D2O and H2O or H2 0 and H2 0). These differences in physical properties manifest themselves in their thermodynamic properties so that the ratios of isotopically substituted compounds represent chemical activity products (a s) that have temperature signiflcance. Exchange reactions are the special class of chemical reactions where the only difference between the reactants and the products is in the isotopically substituted species. The compoimds are otherwise identical. In general, the fractionation factor a is the ratio of isotopes of two substances. Phases 1 and 2 ... 

The molar volumes of isotopically substituted compounds are virtually indistinguishable for most common compounds so that typical light stable isotopic exchange reactions involving solid materials are insensitive to changes in pressure normally encoimtered imder lithospheric conditions making them suitable for geothermometry (the study of temperature within the Earth). 

If the selectively labelled compound is created through admixture of several clearly defined isotopically substituted compounds, this is specified by appropriate subscripts to the nuclide symbols involved. 

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