Deuterium replacing hydrogen atoms

Replacing hydrogen atoms by deuterium atoms confirmed the above mechanism by showing that 95 % of the ammonia formed was NH3 and that for small amounts of N2H4 the hydrogen gas produced was chiefly HD. A lower limit for 2 is 3 X 10 l.mole sec Some experiments were also performed in which hydrazine was replaced by N2O and NH3. The rate coefficient for the disappearance of these molecules was of the order of 10" l.mole sec at 150 °C. 

A peak of mass 32 can form if both of the carbon atoms are replaced by atoms simultaneously. The probability that a molecule of formula C2Hg wUl appear in a natural sample of ethane is (1.08 x 1.08)7100, or 0.01%. A peak that appears two mass units higher than the mass of the molecular ion peak is called the M+2 peak. The intensity of the M+2 peak of ethane is only 0.01% of the intensity of the molecular ion peak. The contribution due to two deuterium atoms replacing hydrogen atoms would be (0.016 x 0.016)7100 = 0.00000256%, a negligible amount. To assist in the determination of the ratios of molecular ion, M + 1, and M+2 peaks, Table 8.3 lists the namral abundances of some... 

Miscellaneous Reactions. The A/-hydrogen atom of diphenylamine is reactive and readily replaced by deuterium by treating with C2H OD. The addition of acid cataly2es the exchange of the hydrogen atoms on the ring system (11). 

Draw structural formulas for all the isomers of ethylene (QH ) in which two of the hydrogen atoms have been replaced by deuterium atoms. Label the cis and the irons isomers. 

Vibrational spectra are often so complicated that assignment of a particular absorption to a given bond is difficult. One way to confirm that an assignment is correct is to carry out selective isotopic substitution. For example, we can replace a hydrogen atom with a deuterium atom. If an iron-hydride (Fe—H) stretch occurs at 1950 cm-1, at what energy will this stretch occur, approximately, for a compound that has deuterium in place of the hydrogen Refer to Major Technique 1, which follows these exercises. 

This mechanism would predict that a plot of l/d>r vs. 1/[BH2] should be linear with an intercept equal to l/Oisc. The experimental results 1 have been plotted in this way in Figure 3.1. The straight lines in Figure 3.1 are consistent with but do not prove the suggested mechanism. The slope for the lower line (BH2) is equal to 0.05, while that for the upper is 0.133. This difference in rate upon replacement of a hydrogen atom with deuterium indicates that the reaction is subject to an isotope effect. Therefore the abstraction... 

Because most common solvents, including water, contain protons, and most NMR analyses involve the measurement of protons, a solvent without protons is generally used in NMR spectroscopy. Commonly, solvents in which the hydrogen atoms are replaced with deuterium (i.e., solvents that have been deuterated) are used, the most common being deuterochloroform. In addition, an internal standard, most commonly tetramethylsilane (TMS), is added to the sample in the NMR sample tube (see Figure 14.3, D) and all absorption features are recorded relative to the absorption due to TMS. 

Replacement of a hydrogen atom by deuterium in 1 butanol by ID has created optical activity. 

Considering the deuterium effect on naphthalene, Ci0H8, in which all the hydrogen atoms are replaced by deuterium, the Franck-Condon factor is decreased and consequently the rate of internal conversion... 

A secondary deuterium kinetic isotope effect is observed when substitution of a deuterium atom(s) for a hydrogen atom(s) in the substrate changes the rate constant but the bond to the deuterium atom is neither broken nor formed in the transition state of the rate-determining step of the reaction. Several types of secondary hydrogen-deuterium (deuterium) KIEs are found. They are characterized by the position of the deuterium relative to the reaction centre. Thus, a secondary a-deuterium KIE is observed when an a-hydrogen(s) is replaced by deuterium [equations (1) and (2)], where L is either hydrogen or deuterium. 

Recently, deuterium isotope effects have attracted considerable attention. In most cases (440) carbon nuclei are shielded when hydrogen atoms in the molecules are replaced by deuterium. A torsional-angle dependence on deuterium... 

In the context of this book our interest is in the isotope effect on the equilibrium constant Kp. This is illustrated below for an isotope effect involving the replacement of a hydrogen atom by a deuterium atom... 

There are three methods that are widely used to follow the rates of isotopic hydrogen exchange in heterocyclic compounds. First, infrared spectroscopy enables the replacement of a hydrogen atom by a deuterium atom within a molecule to be detected. When an —H bond becomes an X—D bond there is a reduction in the stretching frequency... 

Organolithium reagents, like Grigncird reagents, are bases that react with proton (or deuteron) donors. Figure 14-13 illustrates this reaction. In this reaction D2O (heavy water) is the deuterated form of water in which the hydrogen atoms (H) are replaced with deuterium atoms (D). 

Treatment of pyridine with NaOD/D20 at elevated temperatures results in eventual replacement of all hydrogen atoms by deuterium. This process presumably involves deprotonation followed by rapid deuteration of the intermediate negatively charged species (cf. equation 21) in a sequential manner. Azine N- oxides are deuterated in a similar way, positions adjacent to the N- oxide exchanging particularly rapidly. Controlled deprotonation of ring carbon atoms a and y to the heteroatom can be accomplished by the use of strong, non-nucleophilic bases and the intermediate carbanions may be trapped by electrophiles (equation 27). The yields in these reactions are in most cases only moderate, however. As expected, deprotonation occurs more easily if the heteroatom is positively charged. 

With the techniques available at that time, it was not possible to discover whether a single hydrogen atom is replaced by a deuterium atom or whether more extensive exchange occurs during the lifetime of the hydrocarbon molecule on the surface of the catalyst. This type of information became available only after the mass-spectrometric technique of following exchange reactions was introduced. 

Simple or Stepwise Exchange Reactions. In this class of exchange reaction, only a single hydrogen atom is replaced by a deuterium atom in each molecule which reacts on the surface of the catalyst. Isotopic species containing two or more deuterium atoms are formed only by successive reactions. This class of reaction can be recognized in three ways o. The value of M defined by Equation (7) will be unity. h. The only initial product will be the monodeutero species, C Hm iD. c. The interconversion equilibria. Equations (1) and (2), will be satis-... 

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