Nucleophiles amines, hydrogen bonding

The downward curvature observed in this and other systems could be easily explained in terms of a mixed aggregate between the catalyst and the nucleophile. A hydrogen-bond donation to the amide catalyst would render the amine a better nucleophile, up to a value of saturation , after which increasing amounts of catalysts should have no further effect. The results in Table 15 can be easily explained in the same terms, where K measures the equilibrium of the association between the amine and the catalyst. 

One method we have developed for avoiding polymerization with the adsorbed water layer is to use a base catalyzed reaction in supercritical CO2 (SCF CO2). We have shown that SCF CO2 has the unique property of removing all adsorbed water from the silica surface. Once removed the amine base catalyses the reaction of the silane with the surface. As shown in Figure 1, the preadsorbed amine hydrogen bonds to the surface silanol and renders the Si-0 group of the silanol more nucleophilic for reaction with the silicon atom of the incoming chloro or alkoxysilane. Triethylamine is the preferred amine as it binds to all isolated silanols from SCF CO2 and is not removed with subsequent exposure to flowing SCF CO2 solvent. Furthermore a tertiary amine should be used as primary and secondary amines such as ammonia are known to react with CO2 to produce carbamates. " ... 

Together with a shift of the proton from the a-carbon to the alkoxide oxygen, the tertiary amine is eliminated from the addition product to yield the unsaturated product 3. Early examples of the Baylis-Hillman reaction posed the problem of low conversions and slow reaction kinetics, which could not be improved with the use of simple tertiary amines. The search for catalytically active substances led to more properly adjusted, often highly specific compounds, with shorter reaction times." Suitable catalysts are, for example, the nucleophilic, sterically less hindered bases diazabicyclo[2.2.2]octane (DABCO) 6, quinuclidin-3-one 7 and quinuclidin-3-ol (3-QDL) 8. The latter compound can stabilize the zwitterionic intermediate through hydrogen bonding. ... 

Because the tertiary amines cannot be brominated by NBS, they do not influence the o/tAo-bromination of phenols. Though the hydrogen bonding between the phenolic OH and NBS will be formed, the bonding is inferred to be weaker than that between the OH and the (V-bromoamines. The nucleophilicity (or basicity) of the nitrogen atom of A -bromoamines is stronger than that of NBS. This is why traces of A -bromoamines can react with phenols continuously. 

Alkyl methacrylates, hydrolysis of polymeric ester functionality, 259 Aluminum-hydrogen bond, nucleophilic substitution, 264 Amines alkylation, 28 benzyl-group cleavage, 25 Aminomethylation chloromethylated polymers, 19 Deltfpine reaction, 19 Anionic polymerization advantages, 85... 

Figure 5.16 Photoactivation of a phenyl azide group with UV light results in the formation of a short-lived nitrene. Nitrenes may undergo a number of reactions, including insertion into active carbon-hydrogen or nitrogen-hydrogen bonds and addition to points of unsaturation in carbon chains. The most likely route of reaction, however, is to ring-expand to a dehydroazepine intermediate. This group is highly reactive toward nucleophiles, especially amines.

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