Treatment of Hydrogen Atoms

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 

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In deriving eq. (2.2.54), we have skipped some mathematical steps. Recall from the treatment of hydrogen atom ... 

Treatment of Hydrogen Atoms in Neutron Diffraction Studies... 

Weighting scheme in LS refinement Treatment of hydrogen atoms Shift-to-error ratio, (A/(r)niax... 

The treatment of hydrogen atoms in an X-ray structure depends on many things, such as the geometry of the hydrogen atom containing moiety, the temperature of data collection, which influences the X—H distances, and the element t5rpe of the atom bound to hydrogen which also plays a role. 

Neuhauser D, Baer M, Judson R S and Kouri D J 1989 Time-dependent three-dimensional body frame quantal wavepacket treatment of the atomic hydrogen + molecular hydrogen exchange reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surfaced. Chem. Phys. 90 5882... 

All the examples presented under Sect. 4.1 used an iodine atom transfer to generate the desired radicals. Another approach involving abstraction of hydrogen atom is also reported. For instance, ethers and acetals undergo direct intermolecular addition to aldehydes under treatment with Et3B/air... 

Addition of hydrogen atoms in the presence of a metal catalyst to double or triple bonds is known as hydrogenation or catalytic hydrogenation. Alkenes and alkynes are reduced to alkanes by the treatment with H2 over a finely divided metal catalyst such as platinum (Pt—C), palladium (Pd—C) or Raney nickel (Ni). The platinum catalyst is also frequently used in the form of Pt02, which is known as Adams s catalyst. The catalytic hydrogenation reaction is a reduction reaction. 

W. H. Miller Tunneling is surely involved in the present case because the isomerization involves a large amount of hydrogen atom motion. Also, with no tunneling the resonances would be infinitely narrow (and thus unobservable). Our calculations, though, are a fully quantum mechanical treatment and thus do not explicitly identify what is tunneling and what is not. This would only be meaningful in an approximate (e.g., semiclassical) treatment. 

In a forma] sense, silicon might be expected to parallel the extensive alicyclic and aromatic chemistry of carbon, and to some extent it does. Substitution of hydrogen atoms by methyl groups seems to stabilize these systems. A large series of per-methylcyclosilanes can be synthesized by treatment of chlorosihmes with an active metal over a prolonged period of lime ... 

The treatment of the mass spectral data was similar to that of Hightower and Hall (1). The number of hydrogen atoms which had been exchanged per molecule was calculated using ... 

Support-bound triazenes, which can be prepared from resin-bound secondary aliphatic amines and aromatic diazonium salts [455], undergo cleavage upon treatment with acids, leading to regeneration of the aromatic diazonium salts. In cross-linked polystyrene, these decompose to yield nitrogen and, preferentially, radical-derived products. If the acidolysis of polystyrene-bound triazenes is conducted in the presence of hydrogen-atom donors (e.g. THF), unsubstituted arenes can be obtained (Entries 8 and 9, Table 3.47). In the presence of alkenes or alkynes and Pd(OAc)2, the initially formed diazonium salts undergo Heck reaction to yield vinylated or alkynylated arenes (Entry 10, Table 3.47). Similarly, unsubstituted arenes can be obtained by oxida-... 

The acidity difference of hydrogen atoms adjacent to divalent sulfur compared to oxygen stems from the greater polarizability of sulfur and the longer C-S-bond length d-orbitals are not involved. In most cases treatment of dithianes with w-BuLi at temperatures of -30 °C is sufficient for the preparation of the lithio-derivatives. With pKA values of approximately 30, lithiated dithianes can react with aldehydes or ketones, epoxides and acid derivatives, but also with alkyl halides without competing elimination reactions. 

The most satisfactory treatments of hydrogen bonding use either ab initio or semi-empirical molecular orbital theory. The most stable form of the dimer has the configuration shown in Fig. 1 (Shipman et al., 1974 Stillinger and Lemberg, 1975), It is generally assumed, in the absence of information to the contrary, that in water, ice and hydrates one H-atom is collinear with the two oxygen atoms. 

Some of the particular kinetic problems of hydrogen atom abstractions from O—H bonds have been discussed in the context of questions of general interest. The aim has been to make unsolved problems explicit rather than to give final solutions. It seems desirable to realize explicitly that many of our theories and treatments are entirely empirical (Guggenheim, 1938) strongly resembling the entirely empirical origin of the rate constant (Harcourt and Esson, 1866, 1867).4... 

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