Electrophilicity nucleophilic attack

The nitrogen atoms in ADC compounds are highly electrophilic. Nucleophilic attack on nitrogen is easy, and as with electrophilic acetylenes, such as dimethyl acetylenedicarboxylate, it seems likely that some cycloaddition reactions of ADC compounds with unsymmetrical substrates proceed via a stepwise mechanism. PTAD is a powerful electrophile, although TCNE is more reactive, and chlorosulfonyl isocyanate is more reactive still.58... 

Addition of a proton (e.g. p-TsOH, H2S04) or a Lewis acid leads to a more reactive electrophile. Nucleophilic attack of the alcohol gives a tetrahedral intermediate in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester. 

Oxiranes as Electrophiles (Nucleophilic Attack at Ring Carbon)... 

Other reactions suggestive of electrophile-nucleophile attack character include triethylsilane not reacting with ammonia alone, but doing so in the presence of trace amounts of sodamide [230b) and carboxylic acids reacting only in the presence of trace amounts of Lewis acid. 

Step 2 Make a new bond between a w bond and an electrophile. Nucleophilic attack of the enol on the electrophilic halogen molecule, X, gives the conjugate acid of an a-haloketone. 

Eq. (4) provides a simple and direct formalism to obtain the Fukui function from an approach based on a relationship with the FMO s. The condensed Fukui function for electrophilic (nucleophilic) attack involves the HOMO (LUMO) FMO coefficients (c) and the atomic overlap matrix elements (S). 

Among these four positions, only protonation at Cl or at C4 win generate a resonance-stabilized carbocation. So, we must explore protonation at each of these positions. Let s begin with protonation at Cl, which leads to a resonance-stabilized intermediate. When we draw both resonance structures, we can see that two positions are electrophilic. Nucleophilic attack can occur at either of these locations, although the product is the same in either case, leading to only one product ... 

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