Hydrogen attraction

Other examples of polar covalent bonds include C—O, O—H, and N—H. Carbon and hydrogen attract electrons to almost the same degree. Therefore, when carbon is bonded to another carbon atom or to a hydrogen atom, the bond is not usually considered to be polar. For example, C—C bonds are considered to be non-polar. 

An alternative view is provided by a pair of electrostatic potential maps. Electron-rich heteroatoms line up with the electron-poor (acidic) hydrogens. Attraction between the two bases may be thought of as due to favorable Coulombic interactions. 

Alefeld and co-workers (24, 25) have discussed the hydrogen-hydrogen attractive interaction by using the elasticity theory developed for defects in solids by Eshelby and others (46). The strength of the elastic dipole moment is related to the volume expansion resulting from the interstitial hydrogen (25) (Equation 10), where P is the strength of the elastic dipole caused by the interstitial species... 

Other possible oxygen-to-hydrogen attractions causing hydrogen bonding between an alcohol and water molecules... 

The advent of tunable lasers created a radically new situation as to the possibility for selective excitation of high Rydberg states and for making precise measurements on their properties. Highly excited atoms are very sensitive to external fields, and currently used field ionization methods are very powerful for detecting Rydberg states. As a consequence of these circumstances, such an old problem as the Stark effect in atomic hydrogen attracted a renewed interest. 

Note that these reactions are somewhat analogous to addition of the radicals to vinyl monomers.) Similar results were obtained for reactions carried out in benzene and in methanol, the latter showing that fragmentation of photoexcited benzoin and l nzoin methyl ether occurs much more rapidly than hydrogen attraction from methanol. 

Initial formation of radicals by photoinduced hydrogen attraction from the substrate is not in dispute and, as noted in Section 1, hydrogen abstraction from alcohols, ethers and hydrocarbons is effected with high quantum efficiencies by aromatic carbonyl compounds in which the lowest lying triplet level is of n—n type, e.g. benzophenone, anthra-quinone (42 -44). 

As one of the fundamental bond constructions, the carbonyl-ene reaction - between an aldehyde and an alkene bearing an allylic hydrogen - attracts considerable attention [1] from the synthetic community. Given the versatile chemistry of the product homoallylic alcohols, both the intra- and intermolecular versions of asymmetric carbonyl-ene reactions are valuable processes. [2] Within the catalytic field, [3] the continuing development of chiral Lewis acids further advances the utility and scope of carbonyl-ene chemistry. We wish to highlight a number of these developments. 

Fig. 4.10. Schematic side and top view of the electron cloud in a small molecule electron-rich organic semiconductor (e.g. an ohgothophene or an acene). Because hydrogen is more electronegative than carbon the peripheral hydrogens attract the pi electrons leading to a herringbone stacking. The higher permittivity of neighboring standing molecules leads to the nearly vertical orientation for the first few deposited layers.

Walter Heitler and Fritz Wolfgang London convincingly explained why two neutral atoms (like hydrogen) attract each other with a force so strong as to be comparable to the Coulomb forces between ions. Applying the Pauli exclusion principle when solving the Schrddinger equation is of key importance. Their paper was received on June 30,1927, by Zeitschrift fur Physik, and this may be eounted as the birth date of quantum chemistry. ... 

In some cases an intermetallic compound is formed along with the more stable binary hydride instead of the free metal. Buschow, Bouten and Miedema (1) list over 100 intermetallc hydrides that have been prepared and partially characterized. There are several times this many that are known, yet few are really satisfactory for the applications listed above. This paper is limited to transition metal-transition metal type alloys where one metal (A) is the stronger hydrogen-attracting and (B) is the weaker hydrogen-attracting. Examples of A-type metals are early (Illb,... 

Second-phase particles, dispersed in the matrix of the intermetallic compounds, are able to promote as well as to retard activation (Sandrock, 1978). Second-phase particles richer in the hydrogen-attracting element than the main phase will usually promote activation since they form sites favourable to hydride nucleation. They may also serve as canals by means of which the hydrogen enters the bulk of the main phase. Furthermore, if the presence of the second-phase particles leads to an increase in the brittleness of the alloy, the major activation cracks will form more easily and activation can proceed much more rapidly. 

---