One Oxygen Atom

One Oxygen Atom.—2,5-Dihydro-l-benzoxepins (89) have been reported as products of thermolysis of the vinylallylphenols (88), formed possibly via an intermediate such as (90). The products are thermally unstable and isomerize to cis- and /ra j -3-methyl-2-vinylcoumarans (91). Condensation of phthalic 

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The slow step m base catalyzed enolization is formation of the enolate ion The second step proton transfer from water to the enolate oxygen is very fast as are almost all proton transfers from one oxygen atom to another... 

The thiosulfate ion, 820 is a stmctural analogue of the sulfate ion where one oxygen atom is replaced by one sulfur atom. The two sulfur atoms of thiosulfate thus are not equivalent. Indeed, the unique chemistry of the thiosulfate ion is dominated by the sulfide-like sulfur atom which is responsible for both the reducing properties and complexing abiUties. The abiUty of thiosulfates to dissolve silver haUdes through complex formation is the basis for their commercial appHcation in photography (qv). 

Fig. 2. Improvement in 5 achieved by alkoxy substituents. = only carbon atoms H = with one oxygen atom. To convert MPa to (cal/cm ) , divide...

Figure 13.5 A Mg + atom links GTP to the Ras protein. Mg Is coordinated to one oxygen atom each from the p and y phosphates of GTP as well as to the side chains of Set 17 and Thr 35 of Ras. Two water molecules complete the octahedral coordination of Mg.

In both structures the ion is coordinated to six ligands with octahedral geometry. Four water molecules as well as the side chain oxygen atom of a serine residue from the P-loop and one oxygen atom from the (3-phosphate bind to Mg + in the GDP structure. Two of the water molecules are replaced in the GTP structure by a threonine residue from switch I and an oxygen atom from the y phosphate (similar to the arrangement shown in... 

Two Nitrogen Atoms and One Oxygen Atom Synthesis of 1,3,4-oxadiazines 98H(49)557. 

Active Figure 20.1 An alkoxide ion has its charge localized on one oxygen atom and is less stable, while a carboxylate ion has the charge spread equally over both oxygens and is therefore more stable. Sign in at www.thomsonedu.com ro see a simulation based on this figure and to take a short quiz. 

Transfer of a proton from one oxygen atom to another yields a second tetrahedral intermediate and converts the OH group into a good leaving group. 

When a candle is burned, a gas is produced—a gas containing carbon dioxide and water vapor. It is useful to describe such a gas as a collection of molecules, each molecule containing smaller units called atoms. Each carbon dioxide molecule contains one carbon atom and two oxygen atoms. Each water molecule contains one oxygen atom and two hydrogen atoms. Where did these atoms come from Were they present in the candle before it burned ... 

Suppose we burn one molecule of formaldehyde. The one carbon atom, the two hydrogen atoms, and one oxygen atom in the H2CO molecule must appear in the products. Since, among the products, carbon atoms appear only in carbon dioxide, there must be one molecule of C02 ... 

Notice that we have not yet determined the coefficient of 02 we have designated it as y to remind ourselves of this. Since the oxygen atoms must also be conserved and three are required for the products, three oxygen atoms must have been present in the reactants. One oxygen atom was present in the molecule of formaldehyde, so two more are required. It follows that y must be 1. 

Oxepin is the Hantzsch-Widman name for a seven-membered unsaturated heterocycle with one oxygen atom and the numbering follows the convention for monocyclic heterocycles. However, the isomeric benzene oxide has different numbering in agreement with the 7-oxabi-cyclo[4.1.0]hepta-2,4-diene structure, position 1 now corresponds to position 2 in the oxepin. 

The overall hydroxylation or epoxidation reaction catalyzed by cytochrome P450s involves the insertion of one oxygen atom, derived from molecular oxygen, into a C-H bond or into the Jt-system of an olefin, with the concomitant reduction of the... 

In the luminescence reaction of firefly luciferin (Fig. 1.12), one oxygen atom of the product CO2 is derived from the molecular oxygen while the other originates from the carboxyl group of luciferin. In the chemiluminescence reaction of an analogue of firefly luciferin in DMSO in the presence of a base, the analysis of the product CO2 has supported the dioxetanone pathway (White et al., 1975). 

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