Acceptor atom

The very active unstable tin(III) ion is supposed to play an important role in this chain mechanism of tin(II) oxidation. Cyclohexane, introduced in the system Sn(II) + dioxygen, is oxidized to cyclohexanol as the result of the coupled oxidation of tin and RH. Hydroxyl radicals, which are very strong hydrogen atom acceptors, attack cyclohexane (RH) with the formation of cyclohexyl radicals that participate in the following transformations ... 

Dioxygen is a weak hydrogen atom acceptor due to a low strength of the formed 02—H bond (220 kJ mol-1). However, at high temperature (7 >450K) the reaction... 

The MgO+ ion has significant radical character and reacts via electron transfer (equation 32). It is also a potent H atom acceptor, readily reacting with water via H atom abstraction (equation 33, X = HO). A recent combined experimental and theoretical study reveals that the MgO+ ion readily activates the C—H bond of methane to yield MgOH+ as the major product ion (equation 33, X = CH3) as well as Mg+ as a minor product ion via O atom insertion into the C—H bond (equation 34). ... 

The resulting adduct has the same number of valence electrons as the ethane molecule, C2H6, and has the same structure with the two parts of the molecule having rotational freedom around the N— B coordinate bond, or covalent C-C bond in ethane. Coordinate or dative bonds are usually drawn in molecular structures as arrows to represent the direction of the donation process as in donor atom—>acceptor atom... 

Here we consider carbon monoxide as a chemical reducing agent, with the oxidation product being C02 in all cases. Carbon monoxide may act as a reductant in three different ways (1) as a direct oxygen atom acceptor (2) as a two-electron reductant with water as the source of oxygen and (3) as an indirect reductant in which the reducing power of CO is used to make H2 which then carries out the desired reduction. The three ways are shown schematically as (24)-(26) (in (24) [O] represents an oxide source). Equation... 

As it becomes clear from Fig. 15, a diazene-like conformation can be induced through energy transfer of about 300 kJ/mol. It should thus be possible to induce this conformational change photochemically. The diazene-like conformation corresponds to a double-bonded N2 moiety with two lone pairs, which can play an important role as hydrogen atom acceptors in the reduction process. This appears to be most important for a kinetic activation of the first endothermic reduction step. 

Consequently, ozone is a H atom acceptor similar to methyl radical or halogen atoms. This is evidence for the biradical nature of ozone and, hence, for a principal feasibility of the reaction proceeding through an intermediate biradical state by analogy with peroxide radical reactions. It may be expected that ozone as biradical may change to the triplet state readily the mechanism of the reaction through triplet states has not been elucidated yet. 

Molybdenum has a marked predilection for OAT reactions and biomimetic systems have been reviewed. OAT is a concerted two-electron process that results in the oxidation of the oxygen atom acceptor and the reduction of the donor. The most common reactions for Mo are shown in equations (10) and (11). Catalysis results from the couphng of these reactions, leading to net oxidation of X by X O (equation 12, cf. equation 6). Transformations involving oxo-Mo(Vl) and desoxo-Mo(lV) complexes are recent and important developments (see Section 9). 

While indeed a clean photoreduction of COa to CO in the complex (prophos)Cu (C03)Cu (prophos) was observed the concomitant oxidation did not yield oxygen or hydrogen peroxide but phosphine oxide (30). In order to prevent this dead end, phosphines have to be replaced by ligands that do not act as oxygen atom acceptors. For this purpose we selected the tridentate ligand hydrotris (3,5-dimethyl-l-pyrazolyl)borate (Tp ) as a suitable ligand (40). Various Cu(I) and Cu(II) complexes of Tp or other Tp derivatives have been prepared and characterized (41-45). Unfortunately, we were not able to obtain simple carbonate complexes of the Cu Tp moiety (Structure 1). In the presence of COs, Cu Tp underwent a decomposition. 

H-donors located at hydrogen atom, acceptors at heavy atom. Modeled as layer 3 feature with direction constraint and position tolerance... 

A ubiquitous interaction that is electrostatic in nature and commonly occurs in biological systems is the hydrogen bond (see Fig. 1 for examples). It is defined as the interaction between an electronegative atom (acceptor) and a hydrogen atom that is covalently attached to another electronegative atom (donor) (34, 35). At the fundamental level, a hydrogen bond has been... 

Five pharmacophore point types are used to generate PDT fingerprints hydrogen-bond acceptor atom, hydrogen-bond donor atom, acceptor site, donor site, and hydrophobic center. While donor and acceptor atoms are part of the molecule, site points refer to interaction points located on a virtual receptor defined by geometrical criteria [Martin, Bures et al., 1993]. Interfeature distances from 2.5 to 15.0 A are divided into 27 distance bins of equal width (i.e.,... 

Most metal/oxide surfaces are partially hydroxylated in the presence of water vapour and can participate in hydrogen bonding either as a hydrogen atom donor or acceptor. Thus adsorption of hydrogen atom acceptors such as alkyl esters or compounds such as alcohols and carboxylic acids, which can act as either donors or acceptors, leads to friction reduction. 

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