What are the nucleophilic and basic nature of chemical agents?

To understand the basicity and nucleophilic nature of reagents, it is necessary to first distinguish the characteristics of the nucleophilic atom itself and the external influence on it, in most cases, nucleophiles.

The strength of the alkalinity is the same, but the nucleophilicity has a little more influencing factors than the alkalinity. It is necessary to analyze and consider from multiple aspects, for the experimental process, it is necessary to control each variable, so as to prevent any part of it from affecting the experimental results, and distinguish alkalinity and nucleophilicity from the aspects of concept and evaluation method. Under specific conditions, such as in aprotic polar solvents.

, we are able to estimate the nucleophilic capacity of certain nucleophiles based on the characteristics of alkaline strength. For the factors that greatly affect nucleopicity: the degree of influence of proton solvents, nucleophiles, spatial resistance, polarizability, etc., on nucleopinity remains to be studied, and we can say that there are still other factors that affect the nucleophilicity of reagents that have not yet been discovered.

But first of all, it should be clear that although alkalinity can affect the strength of nucleophilicity, and sometimes alkalinity and nucleophilicity are the same, there is no equivalence between the alkalinity and nucleophilicity of reagents. <>

In the study of organic chemistry, it is very important to study the nucleophilic and basic properties of nucleophiles, and it may even affect the mastery of organic chemistry in the future. So we should be clear that nucleophilic and basic are two different concepts, and there may be a relation, but there is no equivalence. We should start from the definition of the two to understand these two concepts, alkalinity, as the name suggests, refers to the ability of the attack reagent to bind to protons, and due to the neutralization of acid and base, it will produce a violent reaction.

However, the nucleophilia of the reagent will be affected by many factors, nucleophilicity belongs to kinetic control, the size of the nucleophilic ability of the nucleophile depends on many factors, the strength of the nucleophilic ability of the reagent, depends on the charge properties, the size of the polarizability, the strength of the alkalinity, as well as the size of the volume occupied, spatial effects, etc. <>

1. The alkalinity of the same group of elements decreases from top to bottom, and the polarizability increases.

2. The nucleophilicity of the reagent is consistent with the alkalinity in the dipole solvent and the polarizability in the proton solvent.

Nucleophilicity refers to negatively charged or lone pairs of electrons.

The reagent is the nucleophile.

The ability to attack electrophilic atoms.

The nucleophilicity of a reagent is influenced by a number of factors. In general, those reagents that are highly alkaline, large in size, highly polarizable, and not easily solvated are nucleophilic. Among them, the alkalinity of the reagent is the acidic base of lewis.

In other words; Solvation is for both protic and non-protic solvents, and the nucleophilicity of the reagent is consistent with alkalinity in non-protic solvents and polarizability in proton solvents.

Overview of Alkalinity:

For a substance, whether it is basic depends on the ability of unpaired electrons to accept protons, for example, in an aqueous solution, OH- ions can accept H+, NH4+ and other ions, thus exhibiting alkalinity; Correspondingly, in non-aqueous systems, such as NH2- ions in liquid ammonia solvents, which can accept NH4+ plasma, also exhibit alkalinity.

In general, the alkaline strength of a substance depends on the size of the ability to accept protons and the shape of the atomic clusters.

For example, NH3 can accept BF3 to form BF3+NH3-, but the stability of this ion is poor, so NH3 is weakly alkaline. NH2- accepts H+ to form a stable NH3, so NH2- is strongly alkaline, in aqueous solution, NaOH and KOH and other alkalinity are equivalent, then such a solvent is called a leveling solvent, and in some solvents can show the difference in alkalinity of different alkalis, such a solvent is called a distinguishing solvent.

The stronger the metallicity of the element, the most ** oxide hydrate.

the more alkaline it is; The non-metallic nature of the elements.

The stronger it is, the more acidic the hydrate of the most ** oxide is.

The alkalinity of some compounds can also be made with O2-anions.

For example, the alkaline size of some industrial slags is expressed by the activity of O2-negative ions.

The above content reference: Encyclopedia - Alkaline.

The above content reference: Encyclopedia - Nucleophilicity.

Apparently, it is different from the group it reacts with. Electrophiles react with electron-rich groups (c=c, c c, aromatic rings include heterocycles), nucleophiles and electron-deficient groups (such as nucleophilic substituted leaving groups, that is, sn1, sn2; There are also carbonyl groups, including aldehydes, ketones, carboxylic acids and their derivatives, cyano)

Essentially, it's the difference in electron density. Electrophiles are generally electron-deficient, such as halogen elemental (think of electrons becoming halogen aniions), hypohaloic acid, hydrogen halide; Nucleophiles are electron-rich, such as SN1 and SN2 are the substitution of negative ions (especially in alkaline environments), and nucleophilic addition is also electron-rich and even negative ions to attack.

Refers to the property of a substance that gains electrons from other molecules or ions or shares electrons with other molecules or ions. The reactions with the participation of electrophiles are all electrophilic reactions, and the common electrophiles are: H+, Cl+, Br+ and other positively charged reagents or Lewis acids (Lewis) such as Bf3, AlCl3, FeF3

acid）；Nucleophilia refers to the ability of negatively charged or lone electron reagents, that is, nucleophiles, to attack electrophilic atoms, for example, ho—ro—, cl—, br—, cn—, r3n—, h2o, roh, etc. are nucleophiles.

Performance of nucleophiles.

In the nucleophilic substitution reaction, the crypto-ascending function of the nucleophile is to provide a pair of electrons to bond with the central carbon atom of Rx, and if the ability of the reagent to donate electrons is strong, the bond is fast and the nucleophilic is strong. The strength and concentration of nucleophiles had no significant effect on the SN1 response. The greater the concentration of nucleophile, the stronger the nucleophilic ability, which is conducive to the SN2 reaction.

The nucleophilicity of the reagent is related to the following factors:

1) The nature of the charge carried by the reagent.

A negatively charged nucleophile has a greater nucleophilic capacity than a neutral reagent. For example, OH-H2O; ro- > roh, etc.

2) Alkalinity of the reagent The more alkaline (the ability to bind to protons) of the reagent, the stronger the nucleophilicity (the ability to bind to carbon atoms). For example: C2H5O- >Ho- >C6H5- >ch3coo-

3) Polarizability of the reagent.

The greater the polarizability of nucleophiles with similar alkalinity, the stronger the nucleophilic ability. Atoms with a large atomic radius have a large degree of polarizability. For example, the polarizability of reagents oh- and sh is oh-< sh, then its nucleophilicity is oh-

Nucleophilicity also requires consideration of steric hindrance.

The ET group is larger than ME, and it will be greatly affected by steric hindrance during space attack, so nucleophilic MEO->ETO-

The alkalinity is related to the strength of the lost electrons, using the conjugated acid base to compare its alkalinity, the conjugated acid of MEO- is MEOH, the conjugate acid of ETO- is ETOH, MEOH is more acidic than ETOH, and the alkalinity of the corresponding conjugate base is weak, so the alkaline ETO->MEO-

A strong nucleophile must be a strong base, and a strong base is not necessarily a strong nucleophile such as T-Buo- is a strong base, but it is a very weak nucleophile.

Both nucleophilic and basic are represented by lone pairs, with nucleophilia referring to the easy proximity of the electron cloud to the carbon nucleus and basic referring to the easy binding of H+.

The fact that the two are usually the same (e.g. nh >h o>hf is the same as nh and nucleophilic), but the opposite is true for elements of the same main group, such as basic cl->br->i- and nucleophilic i->br->cl- (both oxygen and nitrogen), a fact related to the atomic radius.

The main thing is to look at the specific atom, when the atom type is the same, and then look at the density of the electron cloud.

First, alkalinity represents the ability to bind hydrogen protons, while nucleophilicity represents the ability to bind to carbon atoms; Second, the strength of alkalinity is related to the size of the dissociation equilibrium constant of the base, and the strength of nucleophilicity is related to the energy of the reaction transition state. Third, alkalinity is rarely affected by spatial factors, while nucleophilicity is sensitive to the effect of spatial effects. In fact, nucleophilicity involves a wider range than alkaline, and nucleophilia is not only related to alkalinity, but also related to the polarizability of nucleophilic atoms, their steric hindrance, polarity.

First of all, nucleophilicity refers to nucleophiles.

Affinity for carbocations, characterized by lone pairs of electrons. Or negative ions.

Proton solvents are solvents that can ionize protons, such as the most common water, hydrogen sulfide, which is characterized by central atom electronegativity.

larger (O, S), so the protons connected to it are easy to escape;

In this way, the proton solvent can attract lone pairs of electrons or negative ions to the nucleophile, so that the nucleophilic ability of some nucleophiles is reduced. For example, (the following are all negative ions) in terms of basicity, it is F>Cl>Br>i, but nucleophilicity is I>Br>Cl>F, the reason is that the radius of F is relatively small, and the solvent easily surrounds it;

However, for example, there are some ions with less different radii, and their nucleophilicity is the same as the basic order, such as CH3O->HO- (hydroxide. , when the central atom is an atom of the same period, if the charges are equal, the basic order and nucleophilic order are the same, such as r3c->r2n->ro->f-

In general, the smaller the radius, the solvation action.

The more significant, the radius is similar and the charge is equal, then its alkalinity is considered first.