Compare the electrophilic reactivity of several compounds

First of all, your question should clearly describe whether these 4 substances are attacked as electrophiles, or are they attacked and have an electrophilic bonus?

If it is attacked as an electrophile, then the answer is wrong, there is no doubt about it.

If it is a bonus object as an electrophilic bonus, then the answer is correct. That's what you mean by this question. The proposition is also a half-hung water :)) to make it clear :))).

Taking Carbocation as an example, the key to the comparison is the stability of the carbocation intermediate, the intermediate carbocation generated by 2-chloro-1-propene is at the No. 2 position, at this time, the induction makes the electron cloud density on C lower and the stability worse, [but the conjugation of chlorine increases the electron cloud density on C (contributes a pair of electrons, rich electron conjugation system)], thereby increasing the stability, and the conjugation is [opposite] to the induction direction; And the chlorine in 3-chloro-1-propene only induces electron cation to carbocation, reduces the electron cloud, increases the positive charge, and reduces stability, so 2 is more stable than 3, so it is needless to say that the electron absorption induction of three halogens induces carbocation and the carbocation stability is worse. In comparison, the carbocation stability of 2 is poor, because as I just said, +i and -c coexist here, in opposite directions, but +i is larger, so in general, electrons are absorbed (just not as strong as electron absorption), so the intermediate of 2 is not as stable as 1. Eventually:

If you still have any questions, please continue to ask.

Because the double bond in propylene is electron-rich, the electrophile reacts with it more easily. The electronegativity of halogens is strong and the ability to absorb electrons is strong, which reduces the electron density of the double bond. So the order is this.

The comparison of electrophilic addition activity is the pro-point reagent pairkeyof the offense, soElectronics CloudThe denser it is, the easier it is to add electrophilicity.

Electrophilic addition reaction.

EA), abbreviated as electrophilic addition, is an addition reaction caused by an electrophile (positively charged group) attacking an unsaturated bond. In the reaction, the unsaturated bond (double or triple bond) opens and forms two new bonds with another substrate. The most common unsaturated compounds in electrophilic addition are olefins.

and alkynes. <>

Example analysisAddition with halogens

Olefins are susceptible to addition reactions with halogens to form corresponding o-dihalides. Tetrachloroqi carbon solution of alkene sorghum hydrocarbons and bromine.

After mixing, a reaction occurs, which can make the reddish-brown color of bromine fade, and the phenomenon is obvious. This reaction can be used by laboratories to identify olefins.

In the addition reaction with halogens, the addition reaction between fluorine and olefins is too violent, which will lead to the breaking of the carbon chain. Iodine reacts with olefins very hard, so the reaction of olefins with halogens usually refers to the addition with chlorine or bromine. The order of halogen-olefin addition activity was F2>Cl2> Br2>I2.

When ethylene is mixed with bromine in sodium chloride.

When the reaction occurs in the aqueous solution, in addition to the main residue of the main residue is produced 1,2-dibromoethane, there are also 1-chloro-2-bromoethane and 2-bromoethanol.

Order from largest to smallest: pyrrole.

Benzene & Pyridine. Reason: The activity of the electrophilic substitution reaction is determined by the electron cloud on the ring.

The density is determined, the greater the density of the electron cloud, the rate of electrophilic substitution reaction in the hole.

The larger it is, the pyrrole is a five-membered ring, but the electrons are 6, and benzene is a six-membered ring, and its electrons are also 6, so it is easy to see that the dense rot on the pyrrole ring is greater than that of the benzene ring.

6 5 > 6 6), so the activity of pyrrole is greater than that of benzene.

The pyridine ring is also a six-membered ring, and its electrons are also 6, which is the same as the benzene ring (6 6 = 6 6), but there is a heteroatom n atom on the pyridine ring, and the orange trembling ability of n to absorb electrons is greater than c, so the electron cloud density on the pyridine ring is smaller than that of benzene (part of it is absorbed by n), so the activity of pyridine is worse than benzene, and the effect of n in pyridine is like a nitro group.

Ethylene "propylene" vinyl chloride "2 - methapropylene.

Because when the electrophile attacks the double bond, the higher the electron cloud density, the easier it is to carry out, the halogen is the electron-withdrawing atom, and the smaller the atomic radius, the stronger the electron-withdrawing ability, the more halogen atoms are attached to the double-bond carbon, the lower the electron cloud density, and the lower the reactivity.

The reaction rate of the electrophilic addition reaction depends on the electron cloud density of the carbon-carbon unsaturated bond, and the greater the electron cloud density, the faster the reaction rate. When an electron donor group is attached to the carbon atom of the olefin double bond, the reaction activity will increase and the reaction rate will be accelerated, and conversely, when there is an electron withdrawing group, the reaction rate will be slowed down.

Mainly look at the superconjugation effect for the electron action size, double bond linked groups:

Ethylene, hydrogen atoms.

Acetylene, triple bond, alkyne although more than alkene, but the addition reaction with electrophiles is more difficult than alkenes, it is generally believed that because the bonds of the three bonds are more difficult to polarize than the double bonds, it is not easy to give electrons to bind with the affinity reagent. In the hybrid orbital of S and P, the larger the composition of the S orbital, the shorter the bond length, the more difficult it is to polarize, the greater the dissociation energy of the bond, the triple bond carbon atom of alkyne is sp hybrid, and the carbon atom of alkene is sp2 hybrid, so the bond of acetylene is stronger than that of ethylene.

1—propylene, a methyl group linked to a double bond.

1-butene, an ethyl linked double bond.

2-butene, two methyl groups.

For electron action, two methyl groups are greater than ethyl groups and larger than methyl groups.

So electrophilic addition activity: 2-butene, 1-butene, propylene, ethylene, acetylene.

Hope it helps you o(o

Order from largest to smallest: pyrrole, benzene, pyridine.

Reason: The activity of the electrophilic substitution reaction is determined by the electron cloud density on the ring, the greater the electron cloud density, the greater the electrophilic substitution reaction rate, pyrrole is a five-membered ring, but the electrons are 6, benzene is a six-membered ring, and its electrons are also 6, so it is easy to see that the density on the pyrrole ring is greater than that of the benzene ring (6 5 > 6 6), so the activity of pyrrole is greater than that of benzene.

The pyridine ring is also a six-membered ring, and its electrons are also 6, which is the same as the benzene ring (6 6 = 6 6), but there is a heteroatom n atom on the pyridine ring, and the electron-absorbing ability of N is greater than C, so the electron cloud density on the pyridine ring is smaller than that of benzene (part of it is absorbed by N), so the activity of pyridine is worse than that of benzene, and the effect of N in pyridine is like a nitro group.

Targeting rules. For aromatic systems, especially compounds containing benzene rings, when the electrophilic substitution reaction is carried out, the position of the new upper group has a strong selectivity in the case of existing substituents, and the empirical rule summarized by this selectivity is called the localization rule.

The localization law is mainly used to ** the main product of the reaction, and secondly to guide the selection of appropriate synthesis route. For example, m-nitrobromobenzene is synthesized from benzene.

When synthesizing m-nitrobromobenzene from benzene, it is necessary to consider whether bromination or nitration should be considered first. If it is first brominated and then nitrified, o-nitrobromobenzene and p-nitrobromobenzene are obtained. If nitrification is first followed by bromination, m-nitrobromobenzene is obtained.

Descending order:PyrroleBenzene & Pyridine.

Reason: The activity of the electrophilic substitution reaction is determined by the electron cloud on the ring.

The density is determined, and the greater the density of the electron cloud, the rate of electrophilic substitution reaction.

The larger, the pyrrole is a five-membered ring, but the electrons are 6, and benzene is a six-membered ring, and its electrons are also 6, so it is easy to see that the density on the pyrrole ring is greater than that of the benzene ring.

6 5 > 6 6), so the activity of pyrrole is greater than that of benzene.

Brief introduction. The electrophilic substitution reaction mainly occurs on the aromatic system or electron-rich unsaturated carbon, which is essentially the stronger electrophilic group attacking the negative electron system and replacing the weaker electrophilic group. However, for aromatic and fatty systems, the reaction process is also different due to different specific environments.

The substitution silver reactions on the benzene ring (such as halogenation, nitrification, sulfonation, Friedel-Gram reaction, etc.) are all electrophilic substitution reaction processes. It is generally believed that in the electrophilic substitution reaction, the first is the electrophile.

It is dissociated into a positive ion with electrophilicity under certain conditions.

e+。Then E+ attacks the benzene ring, and the electrons of the benzene ring quickly form a complex.

can be understood as a carbocation), the complex still retains the structure of the benzene ring.

The order of electrophilic addition reactivity from large to small is acetophenone,Acetone, acetaldehyde, formaldehyde.

Because the electrophile is attacking the double bond when the electron cloud.

The higher the density, the easier it is to carry out, halogens are electron-withdrawing atoms, and the atomic radius.

The smaller the electron withdrawr, the more halogen atoms attached to the double-bonded carbon, the lower the electron cloud density, and the lower the reactivity.

Features of electrophilic additions

The electrophilic addition reaction (EA), referred to as electrophilic addition, is an addition reaction caused by the attack of an unsaturated bond by a positively charged group of an electrophile. In the reaction, the unsaturated bond (double or triple bond) opens and forms two new bonds with another substrate.

The most common unsaturated compounds in electrophilic addition are olefins.

and alkynes, electrophilic addition has a variety of mechanisms, including carbocation mechanism, ion-pairing mechanism, cyclogallium ion mechanism, and three-center transition state mechanism.

This is mainly because of the electronegativity of the two halogen atoms.

Unlike the atomic radius, the lone electron pairs of bromine tend to overlap with the carbocation p orbital, resulting in the delocalization of the electron cloud, whereas chlorine does not, and for asymmetric electrophilic addition reactions, the reactive cavity generally follows the Marhalanobis rule.

The product is regioselective.

The electrophilic addition activity grip is compared to the pro-point reagent pairkeyof the offense, soElectronics CloudThe denser it is, the easier it is to add electrophilicity. Mainly look at the superconjugation effect for the electron action size, double bond linked groups:

The bond is weak, the electron is less bound by the nuclear segment, and the structure is looser, so as the ** of the electron, it provides electrons to other reactants. When reacting, it is used as a reaction substrate, and the reagent that reacts with it should be an electron-deficient compound.

Addition of propylene to HBR:

CH3-CH=CH2+ HBR CH3-CHBR-CH3 In the first step, HBR ionization generates H and BR ions, hydrogen ions.

As an electrophile, it first attacks the c=c double bond to form the structure of this sample.

In the second step, since hydrogen has already taken a position on one side, bromine can only attack from the other side. According to the Marshalls Rule.

Bromine bonds with 2-carbon, and then hydrogen hits the side of 1-carbon, and the reaction is complete.