Deuterium atomic properties

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

Table 3.1 Atomic properties of hydrogen (protium), deuterium, and tritium...

Many ionic liquids are based on N,N-dialkylimidazolium cations (BMI) which form salts that exist as liquids at, or below, room temperature. Their properties are also influenced by the nature of the anion e. g. BF T PFg. The C-2(H) in imidazole is fairly labile but the C-4(H) and the C-5(H) are less so. Under microwave-enhanced conditions it is therefore possible to introduce three deuterium atoms (Scheme 13.4). As hydrogen isotope exchange is a reversible reaction this means that the three deuterium atoms can be readily exchanged under microwave irradiation. For storage purpose it might be best to back-exchange the C-2(D) so that the 4,5-[2H2] isotopomer can be safely stored as the solid without any dangers of deuterium loss. The recently... 

It is a fundamental property of atomic particles, such as electrons, protons, and neutrons, to have spins. Spins can be classified as + or spin. For example, a deuterium atom, H, has one unpaired electron, one unpaired proton, and one unpaired neutron. The total nuclear spin = j (from the proton) + j (from the neutron) = 1. Hence, the nuclear spins are paired and result in no net spin for the nucleus. For atoms such as H,... 

A considerable amount of data exists on the luminescence properties of excited benzyl [6,83-90,94-97], arylmethyl [91-93,100-108], diphenylketyl [7,109-116], and heteroradicals [117-123] in low-temperature matrices and in room temperature solution. Tables 6 through 11 tabulate both spectral and lifetime information. Where data is available, these tables also include information on the absorption spectra of the excited radicals. Due to the fact that numerous radicals listed in the tables are partially or totally deuterated, structures indicate the number of hydrogen atoms and/or deuterium atoms present. 

Deuterolysis of the boron derivative with acetic acid-di gives m-1,2-pentadiene which has incorporated three deuterium atoms. Thus, chemical evidence appears to support a borabenzene structure. If delocalization of the negative charge generated at the position a to the Si atom into the d orbitals on the silicon occurs, an aromatic system may result. The spectral properties of this system are discussed in a later section. Formation of germacyclopentadiene anion may also involve formation of a bw-electron system. Protonation of the anion generates the starting material. 

For example, there are three distinct kinds of hydrogen atoms, commonly called hydrogen, deuterium, tritium. (This is the only element for which we give each isotope a different name.) Each contains one proton in the atomic nucleus. The predominant form of hydrogen contains no neutrons, but each deuterium atom contains one neutron and each tritium atom contains two neutrons in its nucleus (Table 5-2). All three forms of hydrogen display very similar chemical properties. 

The hydrogen atoms in the vast majority of structures in the CSD are terminal, single-connected atoms and are represented via the atom property (nh) assigned to the relevant non-H atom. In those few cases where hydrogen is connected to more than one other atom, it is treated explicitly in the connectivity tables, i.e. it is regarded as a non-H atom. Deuterium is always treated in this way. The principal source of multi-connected H atoms arises in bridging hydride complexes of transition metals. This situation also occurs, but rarely, where the crystal structure indicates a... 

Like most of the PLP-dependent decarboxylases, these enzymes involve retention of configuration at the a-carbon (Fig. 13). Chang and Snell first observed that histidine decarboxylase catalyzes the conversion of L-histidine to histamine in solvent with the stereospecific incorporation of one deuterium atom from H20 solvent (266). Retention of configuration was tentatively suggested on the basis of a comparison of the optical rotation properties of the deuterated histamine with those of model compounds. This conclusion was later confirmed for histidine decarboxylase from both Lactobacillus 30a and Clostridium welchii by a method that employed diamine oxidase for the configurational analysis of the (a5)-[a- H]histamine resulting from enzymic decarboxylation of (aS)-[of- H]histidine in H2O diamine oxidase catalyzes stereospecific removal of the pro- S) hydrogen at the a-methylene of histamine (267, 2 ) [Eq. (53)] ... 

The additions of HCl or HBr to norbornene are interesting cases because such factors as the stability and facile rearrangement of the norbornyl cation come into consideration. (See Section 4.4.5 to review the properties of the 2-norbornyl cation.) Addition of deuterium bromide to norbornene gives ejco-norbornyl bromide. Degradation to locate the deuterium atom shows that about half of the product is formed via the bridged norbornyl cation, which leads to deuterium at both the 3- and 7-positions. ° The exo orientation of the bromine atom and the redistribution of the deuterium indicate the involvement of the bridged ion. 

An alternative, and possibly more fruitful, approach lies in the study of the redistribution of deuterium atoms accompanying the exchange and addition reactions of simple hydrocarbon molecules. Such studies have been made on evaporated metal films, and exchange patterns characteristic of the metal have been observed [see, for example, (S)], but the relation of the quantities governing these patterns to the properties of the metals used is by no means straightforward. 

Table 1. Some atomic properties of protium, deuterium and tritium.

Deuteroethane distributions have been interpreted in terms of a parameter P, which is the quotient of the rate constants for ethyl to ethene and ethyl reverting to ethane. For molybdenum, tantalum, rhodium and palladium films, a single value of P (respectively 0.25, 0.25, 18 and 28) sufficed to reproduce the observed distribution, assuming that a further deuterium atom is acquired at every opportunity. With other metals, however, two simultaneous values of P appeared to operate, one contributing 30 to 50% of the reaction having a high P value (13.5-18) and another having a much lower P value (0.36-2). This analysis has not however been accorded an interpretation in terms of the metals physical properties or of ensemble sizes and structures responsible for each participant. 

Up to now you have probably (and rightly) assumed that isotopes of an element are chemically identical. They differ only in the number of neutrons in their nuclei chemistry generally depends on charge, orbitals, and electrons. It may come as a surprise to find that this is not quite true. Isotopes may differ chemically, because some chemical properties do depend on atomic mass. However, this difference is only significant for hydrogen—no other element has one isotope twice as massive as another Kinetic isotope effects are the changes in rate observed when a ( H) hydrogen atom is replaced by a ( H) deuterium atom in the same reaction. For any reaction, the kinetic isotope effect (KIE) is defined as... 

---