Conjugation effect

- Mar 24, 2018 -

The conjugated effect, also called the delocalization effect, refers to an electronic effect in the conjugate system in which the distribution of π electrons (or p electrons) in the system changes due to the interaction between atoms. Where the substituents on the conjugated system can reduce the π-electron cloud density of the system, these groups have an electron-withdrawing conjugation effect, represented by -C, such as -COOH, -CHO, -COR; substitution on the general conjugate system The fundamental energy increases the π-electron cloud density of the conjugated system, and these groups have an electron-donating conjugation effect, represented by +C, such as -NH2, -OH, -R

H2C=CH2, the motion range of the two π electrons of the π bond is limited to two carbon atoms, which is called localized motion.

Conjugation effect

Conjugation effect

In CH2=CH-CH=CH2, it can be seen that two isolated double bonds are grouped together. The movement range of π electron is no longer limited to two carbon atoms, but extends to four carbon atoms. It is called delocalization. [2]

As shown, this molecule is called a conjugated molecule. Any atom in the conjugated molecule is affected by external reagents, and other parts can be affected immediately.

The way in which this kind of electrons pass through the conjugate system is called the conjugate effect.

The transmission along the conjugate system is not limited by distance. [3]

Conjugation effect, the change of molecular properties due to the formation of conjugated π bonds is called the conjugate effect. The conjugate effect is mainly manifested in two aspects.

Conjugation energy: The result of the formation of conjugated π bonds reduces the energy of the system and stabilizes the molecule. For example, the CH2=CH-CH=CH2 conjugated molecule has reduced the total energy of the molecule due to the interaction of the pi bond and the pi bond, that is, the energy of the CH2=CH-CH=CH2 molecule is not conjugated to the two. The sum of the energy of the CH2=CH2 molecules is low. The lower value is called conjugate energy.

2 bond length: From the point of view of an electron cloud, the more electron clouds overlap between a given atom, the greater the density of the electron cloud, the more firmly the two atoms bind, the shorter the bond length, and the conjugated. The generation of the π bond tends to average the distribution of the electron cloud, resulting in a shortening of the bond length of the single bond in the conjugated molecule and a long bond length of the double bond. [3]

Conjugation is a kind of electronic effect. The atoms that make up the conjugated system are in the same plane. The p-electron of the conjugated system is not limited to the movement between the two atoms, but occurs in a delocalized manner, causing the molecules of the conjugated system to produce a series of features, such as low intramolecular energy. The stability is high, the bond length tends to be averaged, and the polarity of the conjugated molecular chain alternates under the influence of an external electric field and causes changes in some other properties of the molecule. These changes are often called conjugate effects. Total

Conjugation effect

Conjugation effect

The yoke effect is an effect of electron delocalization in a conjugated system. It is an important electronic effect in organic chemistry. It can change the distribution of electron cloud density in the molecule (coplanarization, tends to average), Can reduce, the bond length tends to average, the refractive index increases, the entire molecule is more stable