Halogens isotope ratios

Partial mass spectra showing the isotope patterns in the molecular ion regions for ions containing carbon and (a) only one chlorine atom, (b) only one bromine atom, and (c) one chlorine and one bromine atom. The isotope patterns are quite different from each other. Note how the halogen isotope ratios appear very clearly as 3 1 for chlorine in (a), 1 1 for bromine in (b), and 3 4 1 for chlorine and bromine in (c). If the numbers of halogens were not known, the pattern could be used in a reverse sense to decide their number. 

Studies of the dependence of on radiofrequency field strength have been demonstrated by Morgan and Strange (e.g. Ref. 149]) to be an efficient method of obtaining chlorine and bromine relaxation times. From plots like that pictured in Fig. 2.4 the halogen relaxation time is obtained through the ratio of slope to intercept. One difficulty in these types of experiments is that for bromine and chlorine two halogen isotopes contribute to the scalar relaxation. In some cases... 

When n >> 1 the above ratio is always unity. For n - 1 the ratio becomes a function of n. Eq. (5.42), although written in a different way, was originally derived by Hertz [40] who was the first to point out the usefulness of studying the different halogen isotopes in studies of exchange rates. Judging from the sparse use of this technique in later publications his pleas were largely unnoticed, however. 

The Spectra of these halogenated species are analogous to the non-halogenated compounds but with extra structure arising from the appropriate isotope ratio pattern. 

Rule 3). The size of the M + 2 peak indicates the absence of sulphur and halogens and the empirical formula C9H10O2 given in Beynon s tables best fits the isotope peak ratios. The number of saturated sites is 9 + 1 - 5 = 5, i.e. one ring and four double bonds. 

The ratio of products (36) and (37) from VNS of hydrogen (Pe) and substimtion of halogen (Px), respectively (Scheme 4), will depend on the strength and concentration of base, provided that the elimination is a kinetically important step in the VNS reaction, namely Pr/Px = kikE[B]/k-ikx. The influence of base will decrease until a constant value Ph/Px = k /kx is reached as kslB] k i. This has been demonstrated for 4-chloronitrobenzene, which undergoes exclusive substimtion of chlorine unless strong base is present to favour the VNS process. The deuterium isotope effect for VNS hydroxylation by Bu OOH, determined as me ratio of H versus D substitution of l-deutero-2,4-dinitrobenzene, varied from 7.0 0.3 to 0.98 0.01 as the base in NH3 was changed from NaOH to Bu OK me former value is consistent with a rate determining E2 process. 

The mass spectra of chlorine- and bromine-containing compounds clearly show the abundance ratios of the stable isotopes 35C1 37C1 = 3 1 and 79Br 81Br = 1 1 in the molecular ions and those ionic fragments which contain halogens (see Section 9-11). 

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