Amines solvation

Magnitudes and Senses of Nonequivalence Observed for (/ )-(-)-Enriched TFPE (la) in Some Chiral Amine Solvating Agents ... 

Chelating extractants owe effectiveness to the attraction of adjacent groups on the molecule for the metal. Anionic extractants are commonly based tin high molecular weight amines. Solvating extractants contain one or more electron donor atoms, usually oxygen, which can supplant or partially supplant the water W hich is altached to the metal ions. 

See also Chapter 4. The molybdenum (II) alkoxides isolated as alcohol or amine solvates of [Mo(OR)2L2] composition are the typical examples of binu-clear clusters with a quadruple metal-metal bond not supported by any bridging ligands. Square planar coordinated (not taking into account the M-M bond) metal atoms are situated exactly in front of each other, which leads to the molecules with eclipsed conformation. 

The azaallyl oiolates, Le. enolates derived ftom ketone imines or hydrazones are synthetic equivalents of the ketone enolates and thus two examples of azaallyl enolates are included in this section. Uthiated cyclcdiexationephenylimine (151) crystallizes out of hydrocarbon solution as the dimeric diisopropyl-amine solvate (152). Significant disorder between the cyclohexyl and the phenyl moieties is obse ed in this crystal structure however, it is clear that there are no V-az yl carbon contacts in this structure. This Uthiated imine structure can be compared with the Uthiated diinethylhydrazone of cyclohexanone... 

The suggestion has been made that LiAlH4 is a covalently bonded species in solution and can undergo reactions of this sort by attack on the Li atom. NaAlH4, which is clearly ionic, does not react in the same way but will give amine solvates, e.g., with tetramethylethylenediamine (NaTMED)AlH4.45... 

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl-lithium reagents. " The molecular and crystal structures of these compounds, stilbene bis(lithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(lithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by X-ray diffraction techniques. Each structure contains two amine-solvated Li atoms located above and below the olefinic bond of a stilbene molecule. The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)—C(7 ) bond, which is ca. 0.01 nm longer than that in trans-stilbene. " The optical and "C n.m.r. spectra of THF solutions of the related dilithium and disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined. " The data can be rationalized in terms of the... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Photoelectron spectroscopic studies show that the first ionization potential (lone pair electrons) for cyclic amines falls in the order aziridine (9.85 eV) > azetidine (9.04) > pyrrolidine (8.77) >piperidine (8.64), reflecting a decrease in lone pair 5-character in the series. This correlates well with the relative vapour phase basicities determined by ion cyclotron resonance, but not with basicity in aqueous solution, where azetidine (p/iTa 11.29) appears more basic than pyrrolidine (11.27) or piperidine (11.22). Clearly, solvation effects influence basicity (74JA288). 

As pointed out by Chapman et the steric requirements of the reagents and the degree of solvation of the substrate at the reacting center should also be considered when comparing the nucleophilicities of different amines toward different substrates. The large number of factors which may be involved clearly call for much more work in this area. 

Alteration of positional selectivity will result from built-in solvation of the transition state by an adjacent carboxyl-related function.Aminations will be so affected by carboxyl, carboxylate ion, carboalkoxy and less so by carboxamido groups (cf. Section I,D,2,b, structure 12.) Other substitutions such as alkoxylations can be so affected by carboxamido and amidino groups (cf. Section I,D, 2,b, structure 14). The effect of the cyclic hydrogen-bonded form (63) of 2-carboxamidopyridine on the reactivity of a leaving group is not known. 

Alkali and alkaline-earth metals have the most negative standard reduction potentials these potentials are (at least in ammonia, amines, and ethers) more negative than that of the solvated-electron electrode. As a result, alkali metals (M) dissolve in these highly purified solvents [9, 12] following reactions (1) and (2) to give the well-known blue solutions of solvated electrons. 

Persulfate (41) reacts with transition metal ions (e.g. Ag, Fe21, Ti31) according to Scheme 3.42. Various other reduetants have been described. These include halide ions, thiols (e.g. 2-mercaptoethanol, thioglycolic acid, cysteine, thiourea), bisulfite, thiosulfate, amines (triethanolamine, tetramethylethylenediamine, hydrazine hydrate), ascorbic acid, and solvated electrons (e.g. in radiolysis). The mechanisms and the initiating species produced have not been fully elucidated for... 

We must also consider the changes in solvation of the ligands which occur upon coordination. If we consider an amine in water, we would anticipate strong hydrogen-bonding. If we compare 1,2-diaminoethane with ammonia, we would expect the latter to be more highly solvated. This corresponds to a more unfavourable enthalpy associated with the desolvation. 

The SnI reactions do not proceed at bridgehead carbons in [2.2.1] bicyclic systems (p. 397) because planar carbocations cannot form at these carbons. However, carbanions not stabilized by resonance are probably not planar SeI reactions should readily occur with this type of substrate. This is the case. Indeed, the question of carbanion stracture is intimately tied into the problem of the stereochemistry of the SeI reaction. If a carbanion is planar, racemization should occur. If it is pyramidal and can hold its structure, the result should be retention of configuration. On the other hand, even a pyramidal carbanion will give racemization if it cannot hold its structure, that is, if there is pyramidal inversion as with amines (p. 129). Unfortunately, the only carbanions that can be studied easily are those stabilized by resonance, which makes them planar, as expected (p. 233). For simple alkyl carbanions, the main approach to determining structure has been to study the stereochemistry of SeI reactions rather than the other way around. What is found is almost always racemization. Whether this is caused by planar carbanions or by oscillating pyramidal carbanions is not known. In either case, racemization occurs whenever a carbanion is completely free or is symmetrically solvated. 

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