How to judge the difficulty of electrophilic substitution reaction?

The size of the electrophilic substitution reaction of heterocyclic compounds with the same structure is determined by the order of the electronegativity of their three heteroatoms, because of the electronegativity o n s, so the order of the electrophilic substitution reaction: furan ring system pyrrole ring system thiophenol. The above substances are all replaced in the A position, while indole is in the B position, which is determined by the different stability of its intermediates.

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.

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.

Free radical electrophilic substitution reaction: The electrophilic substitution reaction mainly occurs on the aromatic system or electron-rich unsaturated carbon, which is essentially a stronger electrophilic group attacking the negative electron system and replacing the weaker electrophilic group. Among them are sulfonation reactions, nitrification reactions, halogenation reactions, and so on.

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.