Isotopic terminology

Appendix 5.1 Relating K, a, 6, and e in stable isotope terminology Appendix 5.2 Derivation of the Rayleigh distillation equation References... 

From this expression, it is obvious that the rate is proportional to the concentration of A, and k is the proportionality constant, or rate constant, k has the units of (time) usually sec is a function of [A] to the first power, or, in the terminology of kinetics, v is first-order with respect to A. For an elementary reaction, the order for any reactant is given by its exponent in the rate equation. The number of molecules that must simultaneously interact is defined as the molecularity of the reaction. Thus, the simple elementary reaction of A P is a first-order reaction. Figure 14.4 portrays the course of a first-order reaction as a function of time. The rate of decay of a radioactive isotope, like or is a first-order reaction, as is an intramolecular rearrangement, such as A P. Both are unimolecular reactions (the molecularity equals 1). 

Using the terminology of Wolfsherg and Stem (1964), the isotopic rate ratio may be expressed as equation (11) ... 

As just demonstrated, exact mass values show some deviation from nominal mass that can be on either side, higher or lower, depending on the isotopes encountered. While the matter itself can be easily understood, existing terminology in this specific field is comparatively vague. 

STEREOCHEMICAL TERMINOLOGY, lURAC RECOMMENDATIONS WEDLER-BOYER ISOTOPE EXCHANGE PROTOCOL... 

One can apply the formalism discussed above to a wide variety of systems to produce a radiometric date. In this book, we will use the word date to mean the time calculated from the ratio of a radioactive isotope and its daughter isotope using the equation for radioactive decay. An age is the time between a natural event and the present. A date becomes a valid age when the conditions described in the previous paragraph are met. This terminology, suggested by Faure (1986), is not always used in the literature, where age and date are often used interchangeably. But there is value to the distinction because it helps a reader understand which numbers are significant. 

H-Cl plus intimate ion-pairs, H+C1-). A mechanism involving concerted attack by the proton and by the chloride ion was proposed. Since the deuterium isotope effect of DC1 was very small, it was suggested28 that the H-Cl bond in the transition state was only slightly weakened. In the present terminology, the mechanism would be regarded as SE2(cyclic), perhaps verging towards SE2(co-ord), viz. 

The first paper dealing with the NMR determination of non-random distribution of deuterium appeared in 1981 and the site-specific natural isotope fractionation studied by nuclear magnetic resonance (SNIF-NMR) terminology was proposed.36 Since this time several review articles on application of deuterium and 13C NMR natural abundance spectroscopy were published.37 1... 

According to International Union of Pure and Applied Chemistry (IUPAC), the terms speciation and chemical species should be reserved for the forms of an element defined as to isotopic composition, electronic or oxidation state and/or complex or molecular structure (Templeton el al, 2000). This classical definition, appropriate to speciation in solution samples, would exclude most speciation studies on solid materials, such as soils and sediments, more properly defined as fractionation studies. The terminology used in this chapter is based on the broader definition of speciation given by Ure and Davidson (2002), which encompass the IUPAC s narrow definition and includes the selective extraction and fractionation techniques of solid samples. 

Use an example and the appropriate terminology to explain the difference between an isotope and a radioisotope. 

The basic terminology used in this review (Fig. 31.1 A) includes the precursor and product, where the precursor can either be labeled or unlabeled. When labeled, the precursor will also be referred to as the source since it supplies tracer to the progressively N enriched product pool. The process of isotope dilution refers to the addition of an unlabeled precursor to the source pool resulting in a decrease in the source isotopic ratio. The precursor could be known, such as for N03 isotope dilution where N02 is the only option, or unknown as with N02 isotope dilution where N03 or NH4+ could be the precursor. Isotopic equilibrium is achieved when the product pool has the same isotopic composition as the precursor pool and it is important to note that isotope dilution fosters this condition. At equihbrium, a rate can no longer be discerned by comparing the isotopic ratios of the pools. As suggested by the unidirectional arrows in Fig. 31.1, an assumption of the tracer method is that isotope recycfing does not occur. However, we know this... 

This mechanism is similar to that proposed for cycloheptatriene replacement in (77-C7Hg)Cr(CO)3 by trimethyl phosphite. By analogy with the isotopic exchange of cycloheptatriene, the probability of a seven-coordinated transition state is rather low, which provides an explanation for the low rate constant other words, using Pearson s terminology 102), the... 

Waters mix conservatively with respect to their isotopic compositions. In other words, the isotopic compositions of mixtures are intermediate between the compositions of the end-members. Despite the terminology (the 8 notation and units of %c) and common negative values, the compositions can be treated just like any other... 

K. Cohen and I. Kaplan in the Ihiited States and is described in The Theory of Isotope Separation by Cohen [C3]. The most important results are summarized in Secs. 8 throu 12 of this chapter, with some changes in terminology and notation. 

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