Nucleophilic dipole

Perhaps the most useful characteristic of these thiocarbonyl ylides is their ability to participate in 1,3-cycloaddition reactions. Huisgen ei al. reported that the diphenyl-1,3,4-thiadiazole 112 underwent loss of N2 at -45 °C to give the ylide 113. The nucleophilic dipole of 113 was then shown to undergo cycloadditions with electrophilic carbon-carbon double and triple bonds <01HCA98I>. 

Type I There is an overlapping of the high-lying HOMO of the dipole with the LUMO of the dipolarophiles. Such a situation is often referred to as a HOMO-controlled dipole or a nucleophilic dipole and includes many commonly used dipoles such as azomethine ylide, carbonyl ylide, nitrile ylide, azomethine imine, carbonyl imine, and diazoalkane. There is a close similarity of these reactions with a normal electron-demand Diels—Alder reaction, which involves the overlapping of the diene HOMO and LUMO of the dienophile. 

Examine the molecular model of ferrocene on Learning By Modeling Does ferrocene have a dipole moment Would you expect the cyclopentadienyl nngs of ferrocene to be more reactive toward nucleophiles or electrophiles Where is the region of highest electrostatic potential... 

I > Br > Cl > F. In nucleophilic aromatic substitution, the formation of the addition intermediate is usually the rate-determining step so the ease of C—X bond breaking does not affeet the rate. When this is the ease, the order of reactivity is often F > Cl > Br > I. This order is the result of the polar effeet of the halogen. The stronger bond dipoles assoeiated with the more eleetronegative halogens favor the addition step and thus inerease the overall rate of reaetion. 

The ease with which the dipolarophile interacts with vinylacetylenes depends mainly on a spatial factor. The study of the reactions of alkylthiobuten-3-ynones-l and their selenic and telluric analogs with DPNT shows that, in this case, nitrilimine also acts as a nucleophilic agent with a nucleophilic center on the carbon atom of the 1,3-dipole and always adds to the terminal carbon of the enyne system to form l,3-diphenyl-5-/ -2-pyrazolenines. The oxidation of the latter with chloranil leads to alkynylpyrazoles (65ZOR51). 

Walden, Paul, 360 Walden inversion. 359-360 Wang resin, solid-phase peptide synthesis and. 1037 Water, acid-base behavior of, 50 dipole moment of, 39 electrostatic potential map of. 53 nucleophilic addition reactions of, 705-706 pKaof, 51-52... 

The addition of methyl 3-amino-2-butanoate to ( )-4-[(5 )-arylsulfinyl]-5-(2-chlorophenyl)-4-penten-2-one in refluxing methanol gave the dihydropyridine as a single diastereomer. The stereochemical outcome is rationalized as occurring from attack of the nucleophile on the conformation in which dipole-dipole repulsion is minimized17. 

There is evidence, both experimental and theoretical, that there are intermediates in at least some Sn2 reactions in the gas phase, in charge type I reactions, where a negative ion nucleophile attacks a neutral substrate. Two energy minima, one before and one after the transition state, appear in the reaction coordinate (Fig. 10.1). The energy surface for the Sn2 Menshutkin reaction (p. 499) has been examined and it was shown that charge separation was promoted by the solvent.An ab initio study of the Sn2 reaction at primary and secondary carbon centers has looked at the energy barrier (at the transition state) to the reaction. These minima correspond to unsymmetrical ion-dipole complexes. Theoretical calculations also show such minima in certain solvents, (e.g., DMF), but not in water. "... 

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