Carbonyl compounds affinity

Additional gas-phase reactivity data, such as gas-phase acidities of alcohols [41], proton affinities of alcohols and ethers [41], and proton affinities of carbonyl compounds [42] could equally well be described by similar equations. 

Alternatively, unreactive mixtures of organosilicon hydrides and carbonyl compounds react by hydride transfer from the silicon center to the carbon center when certain nucleophilic species with a high affinity for silicon are added to the mixture.76 94 This outcome likely results from the formation of valence-expanded, pentacoordinate hydrosilanide anion reaction intermediates that have stronger hydride-donating capabilities than their tetravalent precursors (Eq. 6).22,95 101... 

Notice that the final result is a 1,3 charge affinity inversion Umpolung) of an allylic derivative via a FGI of a functional group of type E by a group of type A, followed by a [2,3]-sigmatropic rearrangement. If the intermediate allyl anion reacts with a carbonyl compound as the electrophile the result is then a 1,4-D system, such as ... 

The intrinsic basicities of cyclopentenone and cyclohexenone (59), and their lactone analogues (60), have been accessed via measurement of their gas-phase proton affinities, and compared with the saturated carbonyl compounds in both cases. The results... 

Basicity in the gas phase is measured by the proton affinity (PA) of the electron donor and in solution by the pAj,. A solution basicity scale for aldehydes and ketones based on hydrogen bond acceptor ability has also been established [186]. Nucleophilicity could be measured in a similar manner, in the gas phase by the affinity for a particular Lewis acid (e.g., BF3) and in solution by the equilibrium constant for the complexation reaction. In Table 8.1 are collected the available data for a number of oxygen systems. It is clear from the data in Table 8.1 that the basicities of ethers and carbonyl compounds, as measured by PA and p , are similar. However, the nucleophilicity, as measured by the BF3 affinity, of ethers is greater than that of carbonyl compounds, the latter values being depressed by steric interactions. 

The reductive method leads to oximes, which may be hydrolyzed to the corresponding carbonyl compound. Ti(III) serves to reduce the N-0 bond, and titanium s strong affinity towards oxygen facilitates the hydrolysis to complete the conversion ... 

Although they are not carbonylic compounds, carboxylate ions should be discussed here in conjunction with the carboxylic acids. Owing to its resonance stabilization, the —COjf group has no low-lying vacant orbital or any positive electron affinity thus it is non-reactive toward e q. Carboxylate ions with aliphatic chains, which may also carry OH or NH2 groups, are evidently non-reactive. This has been shown in the cases of formate, acetate, citrate, lactate, oxalate, glycinate and ethyl-enediaminetetra-acetate ions, all of which react with e q at rates lower than 1O0 m-1 sec-1 (Anbar and Neta, 1967a). 

In Eq. (3) [S]o and [S]f are starting and ending substrate concentrations. S approaches [S] when substrate consumption is minimal, and S is substituted for [S] to correct for excess substrate consumption. In these analyses, however, substrate inhibition can be a problem if the product has a similar affinity to the substrate. Fortunately, most P450 oxidations produce products that are less hydrophobic than the substrates, resulting in lower affinities to the enzymes. There are exceptions, including desaturation reactions that produce alkenes from alkanes (10) and carbonyl compounds from alcohols. These products have hydrophobicities that are similar or increased relative to their substrates. 

Experiments with glucose solutions have shown that the amount of sulfite bound increases when the solutions are heated strongly beforehand. It seems as if the carbonyl compounds derived from glucose are responsible for this, having a greater affinity for sulfite than glucose, and competing successfully with it when only limited amounts of sulfite are available. 

In order to protect the proton, and thereby suppress the kinetically favoured proton transfer route, it has been found out that gas-phase addition followed by elimination can be enhanced by reacting the proton bound dimer of the carbonyl compound rather than the protonated monomer [ 134]. In cases where the carbonyl compound has a higher proton affinity than the nucleophile, proton transfer is of course no problem. Alternatively, if the nucleophile already is protonated, as in the reactions between NH] and various carbonyl compounds, proton catalysed addition/elimination is possible as demonstrated experimentally by observation of immonium ion formation [135-137]. Likewise, the hydrazo-nium ion has been found to react with formaldehyde and a wide range of other aldehydes and ketones [138]. 

Tervalent phosphorus has a high affinity for oxygen and the P=0 bond once formed is very strong. This fact, which also provides the driving force for the Wittig and related reactions, has led to the widespread use of P(III) compounds for direct deoxygenation of epoxides, ozonides, carbonyl compounds, and both N- and 5-oxides.2... 

Due to silicon s higher affinity toward oxygen than carbon, the silyl iodide does not add directly across the vinyl ether double bond, but first reacts with the carbonyl compound to form a silyloxyalkyl iodide (25). In the presence of zinc iodide or iodine, this adduct adds to a vinyl ether, and the resulting vinyl ether-iodide adduct (26) initiates Znl2-mediated propagation (via 27). 

Oftentimes, aldehydes are isolated and purified as their derivatives, and their regeneration is then of importance (cf. method 195). The fission of the oxime, semicarbazone, hydrazone, etc., may be accomplished by acid hydrolysis or by an exchange of the nitrogenous moiety with another carbonyl compound, such as benzaldehyde, for which it has a greater affinity. 

Because of the high discriminating capacity of MAD for sterically and/or electronically similar ethers, Yamamoto and Maruoka examined the affinity of the compound toward other substrates with oxygen-containing functional groups, for example various carbonyl compounds, including both aliphatic and aromatic aldehydes, amides, esters, ethers, and ketones with similar structural substituents. Binding behavior was monitored by low-temperature NMR spectroscopy of these substrates and their... 

The influence of cyclopropyl on the gas phase stability of carbocations as measured by ion cyclotron resonance is shown in Table 14, along with data for some reference compounds. The results are given as gas phase basicities, GB, and proton affinities, PA, defined as AG° and AH°, respectively, for dissociation of the protonated molecule, as in equation 11. In addition hydride affinities D(BH H ) for some cations defined as — AH° for equation 18 are included. For the gas phase basicities and proton affinities the products B are alkenes, amines, nitriles or carbonyl compounds, and thus for these values the stability of the cation is compared to a derivative where the substituent is conjugated with a carbon-carbon or carbon-oxygen double bond, or a nitrogen lone pair, whereas for hydride affinities the products are saturated. 

TABLE 15. Comparative gas phase (GB(g)) and solution phase (SB(,q)) basicities and proton affinities (PA) in kcal mol of protonated carbonyl compounds"... 

Both the oxidant carbonyl compound (acetone) and the substrate alcohol are bound to the metal ion (aluminum). The alcohol is bound as the alkoxide, whereas the acetone is coordinated to the aluminum which activates it for the hydride transfer from the alkoxide. The hydride transfer occurs via a six-membered chairlike transition state. The alkoxide product may leave the coordination sphere of the aluminum via alcoholysis, but if the product alkoxide has a strong affinity to the metal, it results in a slow ligand exchange, so a catalytic process is not possible. That is why often stoichiometric amounts of aluminum alkoxide is used in these oxidations. 

By 1967 the kinetic model for nondissociative thermal electron attachment and revised values for the electron affinities of 16 aromatic hydrocarbons and 7 aromatic carbonyl compounds were reported [24-26]. The ECD Ea values were correlated to theoretical calculations, electronegativities, spectroscopic data, and reduction potentials. The majority of these remain the most precise electron affinities for such compounds. Some values are assigned to excited states based on the multistate model of the ECD postulated in the 1990s [27, 28]. The electron affinities of atoms, molecules, and radicals were reviewed in 1966 [24]. The relative Ea of nitrobenzene, CS2, and SO2 were measured by the thermal charge transfer techniques and the Ea of O2 by photodetachment [30-32]. 

Electron Affinities of Organic Carbonyl Compounds by the ECD Method... 

TABLE 10.10 Evaluated Electron Affinities (in eV) of Esters and Carbonyl Compounds... 

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