Hydroxyl Hydrogens

The resonance of a hydroxyl hydrogen atom is characterized by a variabihty of its chemical shift and in many cases by the absence of any splitting. For example, the chemical shift of the hydroxyl hydrogen atom of ethanol moves depending on experimental conditions, but the chemical shift of the methylene and methyl hydrogen atoms remains unchanged. 

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The hydroxyl hydrogen exchanges but the hydrogen atoms of the CH3 (methyl) group do not. 

Metal alkoxides are compounds in which a metal is attached to one or more alkyl groups by an oxygen atom. Alkoxides are derived from alcohols by the replacement of the hydroxyl hydrogen by metal. 

The hydroxyl hydrogen in phenol is particularly susceptible to abstraction by a free radical. 

C-1-C-2-C-3 but has transferred the C-3-hydroxyl hydrogen, rather than a C-2 ring hydrogen as shown in 15. 

On the other hand, a metastable-ion peak at m/e 88.1 (calculated, 88.0) is present in the mass spectrum of 11 (Figure 8) for the formation of m/e 129 from m/e 189, by loss of acetic acid. In the mass spectrum of the D20-exchanged analog, m/e 129 partially shifts to m/e 130 and partially stays at m/e 129. Metastable-ion peaks are also present at m/e 154.8 (calculated, 154.7) and m/e 97.3 (calculated, 97.3) for the loss of water from m/e 189 followed by the loss of ketene, to give an ion at m/e 129. Since m/e 171 from the loss of water remains at m/e 171, the loss of water must involve the hydroxyl hydrogens. Scheme 3 is an attempt to summarize this in terms of structures which are entirely... 

PbTX-1 also cx)ntains the intermolecular hydrogen bond between hydroxyl 013 and carbonyl 01 already discussed. Only for dihydro PbTX-1 was it possible to locate an 012 hydroxyl hydrogen atom position from difference electron density maps. In that structure a peak appeared at 1.1 A from 012 and 2.1 A from symmetry related 05. 

Typical non-enolising aldehydes are formaldehyde and benzaldehyde, which are oxidised by Co(III) Ce(IV) perchlorate and sulphate , and Mn(III) . The main kinetic features and the primary kinetic isotope effects are the same as for the analogous cyclohexanol oxidations (section 4.3.5) and it is highly probable that the same general mechanism operates. kif olko20 for Co(III) oxidation of formaldehyde is 1.81 (ref. 141), a value in agreement with the observed acid-retardation, i.e. not in accordance with abstraction of a hydroxylic hydrogen atom from H2C(OH)2-The V(V) perchlorate oxidations of formaldehyde and chloral hydrate display an unusual rate expression, viz. 

VALGiMiGLi L, BANKS J T, INGOLD K u and LuszTYK J (1995) Kiuetic solveut effects on hydroxylic hydrogen atom abstractions are independent of the nature of the abstrarting radical. Two extreme tests using vitamin E and phenol, J Am Chem Soc, 117, 9966-71. 

In this section we present preliminary results of CH-jOH reactions with preadsorbed oxygen. Of primary interest is the mechanism for the removal of the hydroxyl hydrogen during formation of the methoxy (CH3O) intermediate. Fig. 4 shows TPRS curves for CH3OH, and... 

Figure 1 Atomic numbering and torsion angles of interest for GalA(l—>2)Rha (left) and GalA(l- 4)GalA (right, plots made with PLUTON [13]). For clarity, most of the hydroxyl hydrogen atoms are not shown.

The alcohol hydroxyl hydrogen typically produced a broad H NMR signal of variable chemical shift which can be eliminated by exchange with deuterium from D20. 

The hydroxyl groups of the cellulose appear to be somewhat acidic. While studies of the composition of alkali cellulose and adsorption of sodium hydroxide have not clearly proved the presence of any sodium compound in alkali cellulose, the reactions of alkali cellulose with carbon disulfide and with etherifying agents would seem to justify the assumption that such an intermediate exists or that the hydroxyl hydrogen at least ionizes. This view is strengthened by the fact that the rate of etherification is proportional to a high power of the concentration of alkali.19... 

A linear hydrogen-bonded structure VIII has also been proposed, but accounts less satisfactorily for the color. The surprising thing about these complexes is the lack of any measurable exchange of the hydroxyl hydrogen atoms from the hydroquinone moiety to the quinone moiety... 

In the second formula the hydroxylic hydrogen is coordinated internally with the carbonyl group, the hydrogen being bivalent. We rather prefer to retain normal valences, and we, therefore, postulate that, in the case of laevo-malic acid, we have the following two formulas... 

Turning our attention to the cis isomer, the Css conformation involves a potential sigma nonbonded interaction between the hybrid in-plane oxygen lone pairs, the Cse involves a hydrogen bond, and the Cee conformation involves a sigma nonbonded interaction between the hydroxyl hydrogen atoms. These interactions are pictorialized below ... 

Once more, replacement of the hydroxyl hydrogen by a group or an atom more electronegative than hydrogen, replacement of the hydroxyl oxygen by its third period counterpart, or, a combination thereof, will enhance n—a interaction and should lead to a preference for the crowded W conformation over the Y con-. formation. This expectation is confirmed by ab initio calculations in which the preferred conformation for NH2OF is found to be the more crowded W con-former314. ... 

Reaction 13.22 is the net result of two steps, the first being the photochemical cleavage of the 0-0 bond in di-terf-butylperoxide (reaction 13.23), followed by the abstraction of the hydroxylic hydrogen in phenol by the ferAbutoxyl radical (reaction 13.24). 

In the A polymorph at room temperature the molecules all lie at crystallographic centers of symmetry, and undoubtedly here too there is hydroxyl hydrogen disorder. The C21, point symmetry, although possible, has not been found in any of the polymorphs. 

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