Oxygen attachment

A major difference between alcohols and thiols concerns their oxidation We have seen earlier m this chapter that oxidation of alcohols gives compounds having carbonyl groups Analogous oxidation of thiols to compounds with C=S functions does not occur Only sulfur is oxidized not carbon and compounds containing sulfur m various oxida tion states are possible These include a series of acids classified as sulfemc sulfimc and sulfonic according to the number of oxygens attached to sulfur... 

A variation on ofloxacin is mfloxacin (20) this compound lacks the methyl group on the 1,8-bridge and contains a sulfur in place of the oxygen attached to the 8-position. Rufloxacin, although less potent than ofloxacin, is well absorbed and has longer half life than does ofloxacin (44—46). 

One of the two carbon atoms of the ethylene bridge of the antidepressants may be replaced by oxygen. Attachment of the side chain via the olefinic linkage found in amytriptyline affords antidepressants with a biologic profile similar to the carbocy-clic prototype. 

When 4-substituted 2,2-dimethyl- 1,3-dioxolanes react with Grignard reagents, the bond that is broken is the one at the oxygen attached to the less-substituted a-carbon. What factor(s) are likely the cause for this regioselectivity ... 

We succeeded in isolating the same adduct reported by Maliepaard et al. in trace quantities, but a 13C-NMR spectrum of the crude reaction mixture revealed the presence of hundreds of additional products (Fig. 7.4). The chemical shift of the guanosine 2-amino adduct (35.4 ppm) is not obvious in this spectrum. The bands of chemical shifts centered at 65 and 55 ppm correspond to structures with oxygen attachment to the C-10 center, but the band of products centered at 28 ppm represented unknown structures. 

FIGU RE 22.21 The heme structure with a molecule of oxygen attached. Note the angular orientation of the oxygen molecule and that the Fe... 

In this expression, p represents the pressure of oxygen (which replaces concentration because oxygen is a gas). If we let / represent the fraction of the available sites that have oxygen attached, the (1 — /) is the fraction of the sites that are still available where oxygen can attach. We can represent the rate of... 

One of the most unusual features of the vitamin B12 structure is that cobalt is bonded directly to carbon. In heme, iron is bonded to five nitrogen atoms, but the sixth position is vacant until oxygen attaches. In vitamin B12, the sixth position is that bonded to the group indicated by R in the structure... 

PhP(OPh)4 Ki = (3 5)xl0-10 and Kz< x. 10 3 mol l-1. In general, the more oxygens attached to phosphorus the less the dissociation of the phenoxyphosphorane. The rate constants for the dissociation of a number of the phenoxyphosphoranes (26) were obtained from a study of thevariable-temperature n.m.r. of equimolar mixtures of the phosphoranes and the related phosphonium triflates RwP(0Ph)4-nCF3S03-.28 Together with the equilibrium constants for these dissociations, these led to the conclusion that the reactions of the cations Rw (OPh)4- with phenoxide ion in acetonitrile proceed with the speed of collision. 

The —OR oxygen is postulated to be the bridging atom because it has the highest basicity among the three oxygens attached to aluminum. 

The ketones have an imbedded signature, a carbon atom with a double-bonded oxygen attached. Acetone (finger nail -polish remover) is the simplest and most common ketone. 

The 8gO is stable if stored at low temperature. This molecule contains an oxygen attached to the normal cyclooctasulfur molecule. The branching of the sulfur ring is quite surprising. The presence of the oxygen, as... 

Hydroperoxylation of silyl dienol ethers was effected by the in t7/ -generated reagent triphenyl phosphite ozonide (Equation 26). The yields are moderate and the products are always accompanied by the hydroxylated equivalents. The mechanism was studied and it was found that the oxygen attached to the carbon came from the central O of the ozonide <2001JOC3548>. 

A somewhat different problem occurs in the question of the structure of, say, the phosphine oxides, the phosphine methylenes or the sul-phoxides. Again in a 3s3p framework the structure of triphenyl phosphine oxide must be written with the oxygen attached by a conventional coordinate link. On the other hand the use of d-orbitals allows the removal of the excess negative charge on the oxygen atom by the formation of a t-bond (Fig. 3). 

One of the most important factors for successful diastereoselection in chiral amide enolate alkylation reactions is the presence of strongly chelated ionic intermediates1 3. The chelation serves the purpose of locking the chiral auxiliary in a fixed position relative to the enolate. The metal counterion is chelated between the enolate oxygen and an additional polar group, anionic, carbonyl or ether oxygen attached to the chiral auxiliary. 

Only a few benzo derivatives are known, and most of them have the oxygen attached to the aromatic rings, i.e. they are cyclic phenol ethers or esters. 3,4,5,6-Tetrahydro-2H-1-benzoxocin (136), mentioned above, can also be obtained by cyclization of o-(bromopentyl)phenol (139) with base. The cyclization is rapid in DMSO and does not require high dilution conditions. The yield of (136) is 30% the alkenyl phenol (140) is obtained in 57% yield (74JOC2598). The latter product is formed by an intramolecular E2 reaction and thus is independent of the concentration of (139). In 75% ethanol solution, more of (136) is formed (64%) and less of (140) (35%), even though the rate of cyclization is much lower than in DMSO (75JA4960). 

Oxidation of Tertiary Amines to Amine Oxides /V-Oxygen-attachment... 

Oxidation of Isocyanides to Isocyanates Oxygen-attach ment... 

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