Reaction History
The electrophilic replacement reaction mainly occurs on an aromatic system or an unsaturated carbon of the rich, in essence, is a strong parental group to negative electronics , Substitution weaker parent groups. However, for aromatic systems and fat systems, their response process is also different due to the specific environment.
1. Replacement reactions on the benzene ring (such as halogenation, nitrification, sulfonation, Fu-gram reaction, etc.) are all prolet reactive reactions. It is generally considered that in the electrophilic substitution reaction, first, the electrophile reagent is dissociated as a positive ion E + of the electrophile under certain conditions. Next E + offensive benzene ring, π electrons of the benzene ring quickly forms the π complex (which can be understood as a carbon positively), and the π complex remained the structure of the benzene ring.
The pental agents E + in the π complex are further joined to a carbon atom of the benzene ring to form a sigma complex. The formation of sigma complex is a result of obtaining two electrons from a benzene ring to a σ key from the benzene ring to the benzene ring from the benzene ring. At this time, this carbon atom having a σ key with the electrophip reagent E + is split into sp 3 hybrid, carbon There are only four π electrons on the ring, that is, four π electrons are distributed on five carbon atoms to form a P-π conjugate system. Therefore, the carbon ring is no longer the original stable conjugate system, but a disadficing electronic conjugate system.
This lack of electron conjugate system has a trend of losing hydrogen protons and restores the original stable conjugate system. Therefore, the sigma complex quickly lost the hydrogen proton, and the carbon atoms formed by the phthalon reagent E + forming a sigma bond again becomes SP 2 Hybrid, returning to the original stable conjugate system.
In summary, the aromatic hydrocarbon electrical substitution reaction can be represented as follows:
2. The antipase of the fat system is different from the aromatic system, and the mechanism is more similar to The aliphatic nucleophilic replacement is generally divided into SE1 and SE2, which is similar to SN1 and SN2 in the mechanism of aliphatic nucleophile. Inserting the Carbin inserted first inserted, the process of eliminating the process is called SE2.
The main reaction
For the electrophilic substitution reaction, its most important reaction type is produced in the aromatic system, so it is only a certain example of the aromatic electrophiles.
Nitrification reaction
Nitrification reaction benzene ring system an important reaction, which is often used to introduce nitro group to the system or to introduce an amino group using nitro group into an amino group. Functional group, strong general use, better positioning, and use the most. Since the nitro has a strong oxidation, and the organic system itself has a certain reducing property, the system is much more likely to become a good explosive material, and the famous TNT, bitter acid, etc. are prepared by nitrification. .
Friedel (Fu Ryder) -Crafts Reaction
This reaction is Charles Friedel and James Crafts Found in 1877, Lewis acid such as aluminum chloride was used as a catalyst at the time, and alkylation or acylation was used. However, through the development, it is now referred to in the aromatic system from a progenic substitution reaction that is carried out under Lewis acid catalysis in the aromatic system.
Fuke reaction may be divided into Fuk-alkylation reaction and a Fuk-acyl-acyl reaction, both of which are introduced into the carbon chain to the aromatic ring. Among them, the alkylation reaction has a severe rearrangement reaction in addition to the carbon donor, and the pure target product is often not available, so the process of agoxylation and reducing is often used.
Halogenated reaction
Hydrogen in the organic compound molecule is referred to as a halogen-substituted reaction, and the mechanism is also a pro-substitute reaction. This reaction is more common in drug modifications, and is also a preparation of the preparation of an aromatic format reagent.
Sulfonated reaction
The hydrogen in the organic compound molecule is referred to as a sulfonating reaction. Benzenes and their derivatives can almost do this reaction, which also belongs to the electrical substitution reaction. However, unlike the above three reactions, the sulfonation reaction has a relatively strong reversibility in the aromatic system, and a positive reaction occurs in the general concentrated sulfuric acid to produce a sulfonic acid group; inverse reaction occurs in the dilute sulfuric acid to remove the sulfonic acid group, therefore often The acid group is used for protecting groups. In addition, during the early chemical process, the reaction is also a pre-drive reaction for producing phenol.
Positioning rules
For aromatic systems, in particular, a compound containing a benzene ring is in the case of a substituent, in the case of a substituent, the position of the new group It is very selective, and the experience rules for this selective summary is called positioning rules.
The positioning rules are mainly based on the effects of substituents on the blendl π electronic cloud density. It is simply divided into a substituent into an adjacent to azimer substituent ( ORTHE- Para Diecting Group ) and interstitial ( Meta Directing Group ), the former makes the new entry group into the benzene ring neighbor orientation, and the latter enters the benzene The inter-loop.
The positioning law is mainly used to predict the main product of the reaction, followed by directing the choice of the appropriate synthetic route. For example, a phenitrophydebenzene is bleed. When the phenyl bisphenitrobiipine is bone, the first bromide is first nitrified. When bromide is then nitrated, it is obtained to obtain intrinsic bromobenzene and p-nitrophenyl bromide. If nitrate is nitrated first, there is a mismiditrobenzene.