Activity of nucleophilic substitution reaction

An important reaction that may occur in RX is SN 1 and SN2 reaction.

The order of activity is: the primary RX activity is the largest, the secondary RX activity is slightly lower, and the tertiary RX activity is the smallest.

It should be pointed out that allyl RX and benzyl RX have great activity in SN2 reaction, which is equivalent to primary RX.

If it is a halogenated hydrocarbon with the same R but different X, whether it is SN2 or SN 1, the reactivity is: RI >；; RBr & gtRCl

This is related to the difficulty of leaving the group. According to this, the activity order of SN reaction in different types of RX can be judged. The reaction between SN 1 and SN2 always goes on at the same time, and the specific situation has a great relationship with the reaction conditions.

A reaction in which an atom or group attached to carbon in an organic molecule is replaced by an atom or group as a nucleophile. During the reaction, the substituted group provides a pair of electrons to form a new bond, while the substituted group leaves with a pair of electrons of the old bond.

Extended data:

The stronger the nucleophilicity of nucleophiles, the higher the concentration and the faster the reaction speed. In polar solvents, SN 1 reaction is easy to occur. This is unfavorable for SN2 reaction. Non-polar solvents are the opposite. Carbocation is more stable in polar solvents than in nonpolar solvents. The intermediate charge of SN2 is dispersed, which is more stable in nonpolar solvents.

Alkyl halide reacts with silver nitrate in alcohol solvent to produce nitrate ester and silver halide precipitate. In this nucleophilic substitution reaction, the negatively charged oxygen atom in nitrate anion nucleophilically attacks the carbon connected with halogen atom, and the halide anion leaves and generates silver halide precipitate.

The step of determining the reaction rate is the dissociation step (the first step), so it is inferred that the reaction is a first-order rate reaction according to the kinetic theory. From the perspective of stereochemistry, if the reactant of this reaction is one of the optical isomers, the inversion probability of the product is slightly greater than 50%.

During the formation of carbon cations, the whole molecule is slightly planar triangle, and nucleophiles can attack from the upper and lower sides of the planar triangle to form new molecules. Therefore, the probability of inversion is 50% in theory, but nucleophiles often form inversion products through reverse attacks because the anions originally separated affect carbon cations.

The reaction is suitable to be carried out in a solvent with strong polarity and weak proton. High polarity helps to stabilize carbon cations by using part of negative charges carried by its own polarity, and weak proton solvents provide protons to combine with stronger nucleophiles (usually separated) to help the reaction balance move to products.

Baidu encyclopedia-nucleophilic substitution reaction