Local nucleophilicity index

The nucleophilicity of 32 amine, amide, carbamate, amidine, and pyridine nucleophiles was calculated at the B3LYP/6-31G(d,p) level of theory using the gas-phase ionization potential based on the nucleophilicity index The correlation coefficient for the calculated pyridine nucleophilicity against Mayr s values was 0.947, and it was 0.987 against the inverse of the electrophilicity scale Mm. The site selectivity predicted for the nucleophiles with more than one nucleophilic centre correlates well with that predicted by the local nucleophilicity index and the philicity index m. ... 

Evaluation of the only appropriate Fukui function is required for investigating an intramolecular reaction, as local softness is merely scaling of Fukui function (as shown in Equation 12.7), and does not alter the intramolecular reactivity trend. For this type, one needs to evaluate the proper Fukui functions (/+ or / ) for the different potential sites of the substrate. For example, the Fukui function values for the C and O atoms of H2CO, shown above, predicts that O atom should be the preferred site for an electrophilic attack, whereas C atom will be open to a nucleophilic attack. Atomic Fukui function for electrophilic attack (fc ) for the ring carbon atoms has been used to study the directing ability of substituents in electrophilic substitution reaction of monosubstituted benzene [23]. In some cases, it was shown that relative electrophilicity (f+/f ) or nucleophilicity (/ /f+) indices provide better intramolecular reactivity trend [23]. For example, basicity of substituted anilines could be explained successfully using relative nucleophilicity index ( / /f 1) [23]. Note however that these parameters are not able to differentiate the preferred site of protonation in benzene derivatives, determined from the absolute proton affinities [24],... 

Finally, the global and local electrophilicity indexes may be also used to describe the nucleofugality of classical leaving groups in organic chemistry. This potential application incorporates the important families of nucleophilic substitution and elimination reactions. This study is however a bit more complex than the cases presented in this review, because the systematization of nucleofugality within an absolute scale requires an important number of requisites that must be fulfilled, most of them regarding the different reaction mechanisms involved in these complexe reactions. 

The issue of regiochemistry can be addressed by identifying sites of local electrophilicity and local nucleophilicity. This was done by calculation of a local electrophilicity index The index of nucleophilicity can be taken as / , the local Fukui function for electrophilic attack. The regiochemistry is then predicted by matching the highest local electrophilicity in the electrophilic component with the largest f for the nucleophilic component. Table 10.10 gives some values of representative dienes and dienophiles. 

Normally the polarity of the normal electron demand DA process has been studied by means of global electrophilicity index difference between reactants and the regioselectivity of the normal electron demand DA reaction using the local electrophilidty index for dienophiles (electrophiles in the reaction) and the local nudeophilicity index for dienes (nucleophiles in the reaction). 

Fig. 5 Local electrophilicity index, condensed on the radical center, ca%, for a total of 47 radicals in gas phase and different solvents. The arrows point to those radicals for which the Fukui function for a nucleophilic attack fic shows the biggest increase, going from gas phase to water...

Orientation in electrophilic and nucleophilic reactions of aromatic compounds can be predicted with the aid of the reactivity index of MO theory. Electrophiles will attack positions of higher electron densities, larger superdelocalizability (electrophile), and the lower localization energy (electrophile). On the other hand, nucleophilic attack is preferred at positions of lower electron densities, larger superdelocalizability (nucleophile), and lower localization energy (nucleophile). Table XXIII shows reactivity indexes of some aromatic nitrogen cations. 

From the relation between Fukui function and local softness, electrophilic and nucleophilic local softnesses can be computed. Donor and acceptor sites can also be identified by large values of both types of local softnesses in addition, it can be used to compare sites of different molecules and to identity which one is softer or harder. The elec-trophilicity index can also be extended to a local context,21 and a comparison of the electrophilicity of sites in different species can be made. 

It is also interesting to examine the effect that the electron-releasing groups may have on the local electrophilicity pattern in ethylene 29. These systems have some importance in the IED processes. Consider for instance the electron-rich ethylenes 33 and 35. On the basis of the Fukui function alone, methyl vinyl ether 33 shows nucleophilic activation at the C2 carbon, fk = 0.470. Dimethylvinylamine 35, on the other hand, displays a similar local reactivity pattern, fk = 0.411. Note that on the basis of the to index, both compounds are predicted as marginally electrophilic. Both compounds 33 and 35 are... 

The electronic chemical potential /x, chemical hardness 17, and global electrophilicity 10 for the dipoles 83-86 are displayed in Table 11. Also included in Table 11 are the values of local electrophilicity and the values of the Fukui function for an electrophilic attack and for a nucleophilic attack fk at sites k for these dipoles. The two dipo-larophiles present similar electrophilicity values, 1.52 eV (14) and 1.49 eV (15) (see Table 1). According to the absolute scale of electrophilicity based on the co index,39 these compounds may be classified as strong electrophiles. 

The r-nucleophilicity and electron-transfer oxidation of silyl enol ethers and ketene silyl acetals has been studied by DFT, focusing on local softness and local nucle-ophilicity index as parameters for intramolecular reactivity and the corresponding group parameters for intermolecular reactivity. ... 

Where Chomo.tce is the HOMO energy of tetracyanoethylene (TCE) taken as a reference molecule because it exhibits the lowest HOMO energy in a large series of molecules previously considered in the framework of polar DA cydoadditions). N is the global nudeophilidty index and is its local counterpart. This nudeophilicity index has been useful to explain the nucleophilic reactivity of some molecules towards electrophiles in cycloaddition as well as substitution reactions. (Domingo, et al, 2008)... 

According to the global electrophilicity index co shown, the dienes will act as nucleophiles and the dienophiles as electrophiles. To study the regioselectivity we used the local... 

With this background in this review we will now talk about the basic theory of the reactivity index including definitions of local and global softness along with relative nucleophilicity and electrophilicity. We will as well cover the role of response function in deriving the excited state reactivity index theory, followed... 

Pertrifluoroacetic acid, produced in situ from HP and trifluoroacetic anhydride, is an efficient reagent for B V oxidation of butanone to yield ethyl acetate. The possible mechanism of the oxidation of aliphatic ketones by pertrifluoroacetic acid is discussed. Several organic reactions, including BV oxidations, have been studied by using reactivity and selectivity indexes proposed in the DFT. The concepts of electrophilicity and nucleophilicity have been applied as reactivity descriptors. The local hardness has been applied as well as a selectivity descriptor. The reactivity and selectivity patterns have been studied for the reactants involved in these organic reactions. They have been ranked in theoretical scales, which are comparable with experimental results obtained from... 

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