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Covalently bonding centers

Covalently Bonding Centers. In some cases, the intermediates may be covalently bonded to the catalyst (86), oftentimes at surface hydroxyl groups. Such reactions are less well characterized in natural systems and would likely lead to mineral/organic systems rather than separated products. [Pg.20]

Protonated methane (CH ) does not violate the octet rule of carbon. A bonding electron pair (responsible for covalent bonding between C and H atoms) is forced into sharing with the proton, resulting in 2 electron-3 center bonding (2e-3c) (see Chapter 10). Higher alkanes are protonated similarly. [Pg.100]

FIGURE 16.9 Examples of covalent bond formation between enzyme and substrate. In each case, a nucleophilic center (X ) on an enzyme attacks an electrophilic center on a substrate. [Pg.509]

The oxygen atom O-1 adds to the carbon-carbon double bond, while the oxygen 0-2 forms a covalent bond to the titanium center. As a result complex 5 is... [Pg.255]

Polar reactions occur because of the electrical attraction between positive and negative centers on functional groups in molecules. To see how these reactions take place, let s first recall the discussion of polar covalent bonds in Section 2.1 and then look more deeply into the effects of bond polarity on organic molecules. [Pg.142]

Cyclazines are conjugated cyclic molecules in which planarity is secured by three covalent bonds to a central nitrogen atom. They differ in the size of the individual ring units. In the nomenclature of cyclazines, the name is preceded by the number of jt-centers between the points of attachment to the nitrogen which are arranged by increasing number and put in brackets, e.g. [3.3.3]cyclazine (1) and [2.3.4]cyclazine (2). [Pg.576]

FIGURE 5.21 The structure of diamond, Each sphere represents the location of the center of a carbon atom. Each atom is at the center of a tetrahedron formed hy the sp1 hybrid covalent bonds to each of its four neighbors. [Pg.313]

The inhibition of brain cholinesterase is a biomarker assay for organophosphorous (OP) and carbamate insecticides (Chapter 10, Section 10.2.4). OPs inhibit the enzyme by forming covalent bonds with a serine residue at the active center. Inhibition is, at best, slowly reversible. The degree of toxic effect depends upon the extent of cholinesterase inhibition caused by one or more OP and/or carbamate insecticides. In the case of OPs administered to vertebrates, a typical scenario is as follows sublethal symptoms begin to appear at 40-50% inhibition of cholinesterase, lethal toxicity above 70% inhibition. [Pg.245]

Triphenylphosphonium ylide reacts with the silylene complex 93 which has a highly electrophilic silicon center, to give the corresponding cationic adduct 94 [115]. The lengthening of the PC bond indicates a loss of the double bond character of the ylide and corresponds to the formation of a tetrahedral silicon center with four covalent bonds (Scheme 28). [Pg.64]

In principle this is the method that gives rise to the strongest support-complex interaction. We have considered in this category all the methods in which the support compensates for at least one of the charges of the complex, usually due to the metal, although without considering the exact nature of the metal-support bond, i.e., purely ionic or polarized covalent. In any case, the only possible covalent bond between support and complex would be estabhshed with the metal center, not with the chiral hgand. [Pg.152]

For practical reasons, the best scenario is associated with spontaneous substrate racemization. This is often the case for compounds possessing a-stereogenic center bearing an acidic proton adjacent to an activating carbonyl group. When this process is too slow, the substrate must be modified or racemization can be achieved by a reversible cleavage of covalent bonds such as the cleavage of cyanohydrins. [Pg.102]

The short lifetimes of carbon-centered monoradicals are generally reduced in the case of diradicals due to their propensity to form covalent bonds. It has been suggested that stable diradicals may be observable from highly strained bicyclic molecules where the TS for inversion is a diradical. Unfortunately, only persistent diradicals have been obtained in this way. Akin to this approach, in a recent attempt to generate the oxyallyl diradical, Sorensen and co-workers synthesized two substituted bicyclobutanones hoping to stretch and homolytically break the central bond using bulky substituents, which would also stabilize the diradical. Though the bicyclobutanones did not yield the desired oxyallyl derivative, the X-ray structures showed... [Pg.301]


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See also in sourсe #XX -- [ Pg.14 ]




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Covalently bonding centers, effect

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