Deuterium nucleus

These absorb at completely different frequencies, and since deuterium and proton chemical shifts are identical (also because deuterium is a spin-1 nucleus), deuterium NMR spectra are hardly ever measured. 

The final state nucleus (deuterium in its ground state) in the reaction p + p —> d + e+ + z/e, has JJ = 1 +, with a predominant relative orbital angular momentum If = 0 and Sf = 1 (triplet S-state). For a maximally probable super-allowed transition, there is no change in the orbital angular momentum between the initial and final states of the nuclei. Hence for such transitions, the initial state two protons in the p + p reaction must have /j = 0. Since the protons are identical particles, Pauli principle requires S) = 0, so that the total wave-function will be antisymmetric in space and spin coordinates. Thus, we have a process Si = 0, Z = 0 >—>, S y- 1,/y- 0 >. This is a pure Gamow-... 

What we do change is the weight of the atom. In the case of hydrogen, there are 3 isotopes ordinary hydrogen with only a proton in the nucleus deuterium, which also has a neutron and which has, therefore, a weight of about two and radioactive tritium, which has a weight of about three and has 1 proton and 2 neutrons in its nucleus. 

Temperatures required for fusion reactions exist in stars where fusion reactions are the principle components of energy release. In the Sun, approximately 90 percent of solar energy is a result of proton-proton interactions in several steps to form helium of mass number 4. These steps all involve binuclear collisions since multinuclei collisions are very improbable events. Initially, two protons interact to form a deuterium nucleus (deuterium is an isotope of hydrogen with one proton and one neutron the nucleus is a deuteron) that collides with another proton to form a He (tritium) nucleus. This nucleus collides with a neutron or another He nucleus (with the emission of two protons) to form He. The net reaction can be represented as four protons fusing to form a He nucleus releasing 26.7 MeV. When a sufficient number of the He and He nuclei are formed in the star, they begin fusion reactions to form heavier nuclei such as Li and Be. The number of proton-proton fusion reactions in the Sun amounts to... 

Often, nuclear equations are written in a shorthand form. An example of this nomenclature is given below for the reaction between uranium-238 and a deuteron, the nucleus deuterium or heavy hydrogen, which produces neptunium-238 and two neutrons ... 

Contrary to the first hypothesis of Dalton s atomic theory, atoms of a given element do not all have the same mass. Most elements have two or more isotopes, atoms that have the same atomic number (Z) but different mass numbers (A). For example, there are three isotopes of hydrogen, called hydrogen (or protium), deuterium, and tritium. Hydrogen has one proton and no neutrons in its nucleus, deuterium has one proton and one neutron, and tritium has one proton and two neutrons. Thus, to represent the isotopes of hydrogen, we write... 

Deuterium labeling of certain positions in the steroid nucleus can be a serious problem if suitably functionalized starting materials are not available or if a particular part of the molecule to be labeled is unsuitable for the various reactions described previously in this chapter. In these cases, the only practical solution to this problem is to incorporate the appropriately labeled carbon fragment by synthesis of the desired skeleton. 

Consider a reactant molecule in which one atom is replaced by its isotope, for example, protium (H) by deuterium (D) or tritium (T), C by C, etc. The only change that has been made is in the mass of the nucleus, so that to a very good approximation the electronic structures of the two molecules are the same. This means that reaction will take place on the same potential energy surface for both molecules. Nevertheless, isotopic substitution can result in a rate change as a consequence of quantum effects. A rate change resulting from an isotopic substitution is called a kinetic isotope effect. Such effects can provide valuable insights into reaction mechanism. 

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. 

Jardine and Brown reported that the product obtained on treatment of indole magnesium iodide in ether with deuterium oxide in tetrahydrofuran was deuterated to the extent of about 50% in both the 1- and 3-positions of the indole nucleus. ... 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

All atoms of a given element have the same number of protons, hence the same atomic number. They may, however, differ from one another in mass and therefore in mass number. This can happen because, although the number of protons in an atom of an element is fixed, the number of neutrons is not. It may vary and often does. Consider the element hydrogen (Z = 1). There are three different kinds of hydrogen atoms. They all have one proton in the nucleus. A light hydrogen atom (the most common type) has no neutrons in the nucleus (A = 1). Another type of hydrogen atom (deuterium) has one neutron (A = 2). Still a third type (tritium) has two neutrons (A = 3). 

In a nuclear reaction of the type called nuclear fusion, two nuclei come together to form a larger nucleus. For example, deuterium nuclei,... 

Because isotopes of the same element have the same number of protons and the same number of electrons, they have essentially the same chemical and physical properties. However, the mass differences between isotopes of hydrogen are comparable to the masses themselves, leading to noticeable differences in some physical properties and slight variations in some of their chemical properties. Hydrogen has three isotopes (Table B.2). The most common ( H) has no neutrons so its nucleus is a lone proton. The other two isotopes are less common but nevertheless so important in chemistry and nuclear physics that they are given special names and symbols. One isotope (2H) is called deuterium (D) and the other ( H) is called tritium (T). 

Another separation method in using nonselective relaxation-rates is based on deuterium substitution, and utilizes the fact that the efficiency with which a nucleus contributes to the relaxation of a neighboring nucleus is proportional to the square of the magnetogyric ratio of the donor nucleus, that is, Phd/PHH = /3(yo/yn) - Because yo/yn — l/, replacement of a proton by a deuterium nucleus would be expected to contribute to the... 

Deuterium ( H) is the most common lock signal. H, Li, and F have also been employed for this purpose. Can we use a nucleus as lock signal while recording a spectrum of the same nuclei ... 

Resolvable modulation is detected on a three-pulse echo decay spectrum of predeuterated 3-carotene radical (Gao et al. 2005) as a function of delay time, T. The resulting modulation is known as ESEEM. Resolvable modulation will not be detected for nondeuterated P-carotene radical since the proton frequency is six times larger. The modulation signal intensity is proportional to the square root of phase sensitive detection and interfering two-pulse echoes and suppressed by phase-cycling technique (Gao et al. 2005). Analysis of the ESEEM spectrum yields the distance from the radical to the D nucleus, a the deuterium coupling constant, and the number of equivalent interacting nuclei (D). The details related to the analysis of the ESEEM spectrum are presented in Gao et al. 2005. 

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