Nucleophilic displacement reactions in aromatic systems. Part IV. Kinetics of the reactions of o- and p-halogenonitrobenzenes with piperidine and with morpholine

Abstract

of the Reactions of oand p-Halogenonitrobenzenes with Piperidine and with Morpholine.

The Element Effect Revisited: Factors Determining Leaving Group Ability in Activated Nucleophilic Aromatic Substitution Reactions

“…17,19,22,23 In fact the distance between the N-H proton and the departing fluoride, 2.42 Å in our transition states, is 0.3 to 0.4 Å shorter than for the other halogen transition states and offers a further small advantage for the fluoro substrate. This conclusion underlines the propensity of partially negative fluorine to engage in stabilizing H-bonding interactions be they intramolecular or intermolecular, e.g., by solvation.…”

Chlorine Isotopie Exchange between Lithium Chloride-36 and 2, 4, 6-trinitrochlorobenzene in £thanolic Solution

“…The mechanism of nucleophilic substitution of aromatic halogen derivatives activated by nitro-groups has been studied extensively [7][8][9]. In the case of chlorine iso-topic exchange between 2, 4, 6-trinitrochlorobenzene and lithium chloride, the reaction probably proceeds by a two-stage bimolecular mechanism, of which the rate determining step is the second order reaction forming a symmetrical σ-complex / which possesses approximately tetrahedral configuration at the site of substitution.…”

“…6 kcal mole -1 . If the general assumption is made that the effect of a substituted nitro-group is to decrease the energy of activation for chlorine exchange by ~ 6 kcal mole -1 [8,10,11], the fact that no exchange has been observed with o-nitrochlorobenzene and with chlorobenzene [2] can be appreciated. The very strong activating influence of nitro-groups on the nucleophilic replacement of aromatic halogen substituents has been satisfactorily explained [12] in terms of the generally recognized inductive and mesomeric effects.…”

“…The fact that o-nitrochlorobenzene undergoes a chlorine exchange reaction at a rate too slow for convenient measurement corresponds with the relatively weak nucleophilic character attributed to the chloride ion [9,13]. Strong nucleophiles, such as piperidine [8] or methoxide ion [10] react readily with the compound.…”

“…The solution is passed through a cation exchange resin column of Diaion SK (8). The copper ions adsorbed on the resin are eluted with 2 Ν hydrochloric acid (9).…”