Conjugation (chemical meaning)

- Mar 31, 2018 -

Conjugation occurs in mathematics, physics, chemistry, geography and other disciplines. Intent: The shelf on the back of the two cows is called a yoke. The yoke allows two cows to walk synchronously. Conjugation is a pair that matches a certain rule. The popular point is that of deafness. In physics, two objects that are symmetrical about an axis are generally described.

Normal conjugate

Also called π-π conjugate. It refers to the dissociation of the electrons that occur when two or more double bonds (or triple bonds) are linked by a single bond. Ingold, C.K., called this effect the mediating effect, and believes that the displacement of this electron in the conjugate system is determined by the electronegativity of each atom and the size of the p-orbit (or main quantum number). Accordingly, if the following electron dissociation occurs in a simple normal conjugation system: (for example, CH2 CH-CH CH2 CH2 CH CH-O). The greater the electronegativity of the Y atom and its p-orbital radius, the greater its ability to attract electrons, and the more favorable the conjugate effect of the group—XY from the reference double bond AB—attracting electrons (as shown by the arrow on the right Show). In contrast, if the electronegativity of the A atom and its p-orbital radius are larger, the smaller its ability to release electrons to move toward the Y atom, the less favorable is the conjugation effect of electron donation toward the -XY group. . The properties of the intermediate atoms B and X are also directly related to the conjugate effect.

Multielectron conjugation

Also known as p-π conjugate. In a simple multi-electron conjugated system, Z is an atom or group with a pair of p electrons (or n electrons). In such a conjugated system, except that Z can form a p-π conjugate, there is a conjugate effect of electron donation to the reference double bond A=B— (for example,

The figure below, etc.) The effect of a pair of p electrons on the Z atom is similar to the -XY group in a normal conjugated system.

Properties: Conjugation of π bond with p orbitals on adjacent atoms. It is divided into three types: multi-electron, electron-deficient and other electronic p,π-conjugate. For example, the conjugation system of vinyl chloride, CH2=CH-Cl, is composed of three atoms (C, C, Cl) and four p electrons (two π bonds and two chlorine atoms) and are conjugated to π bonds. The number of p-electrons is more than the number of atoms of the conjugated bond, which is called multi-electron p,π-conjugated. If the p orbital conjugated to the π bond is an electron-deficient empty orbit, the number of p-electrons forming a conjugated π-bond is less than the number of atoms of the conjugated chain, known as electron-deficient p,π-conjugated, such as allylic. Positive ions CH2=CH-CH2. The allyl radical CH2=CH-CH2, then the number of atoms that make up the conjugated chain is equal to the number of p electrons, which is called isoelectronic, p, π-conjugated. The p,π-conjugation results in the stabilization of the molecule and the equalization of the bond length, known as the p,π-conjugation effect.

Hyperconjugation effect

Also known as conjugate, it is a conjugation phenomenon in which the valence electrons of a C—H bond of an alkyl group overlap with adjacent valence electrons (the carbon atom of an alkyl group is combined with a very small hydrogen atom, For the shielding effect of the electron cloud is small, a pair of electrons on the C—H bond on the alkyl group are attracted to each other by the action of the nucleus. At a certain distance, several CH bond electrons on the alkyl group are mutually exclusive, if there is a nearby π orbital. Or the p orbital can contain electrons, where the σ electrons deviate from the original orbit and are biased towards the π orbit or the p orbit. According to the theory of multi-electron conjugation, a C—H bond or the entire CH group can be viewed as a pseudo-atom, such as the Z atom in the formula: (eg, CH2═CH—CH3, OCH—CH3, etc.). The hyperconjugation effect exists in compounds where the alkyl group is attached to an unsaturated bond, the size of the hyperconjugation effect is determined by the number of -H atoms in the alkyl group, the methyl weakest hyperconjugation effect, and the tertiary butyl group. The strongest hyperconjugation effect. The hyperconjugation effect is much weaker than the normal normal conjugation effect and the multiple electron conjugation effect. (Divided into σ-π and σ-p, σ-π is the most common)

Conjugate effect

Also called p-p conjugate. In addition to the hyperconjugation effect, alkyl groups above the methyl group may also produce the same conjugation effect.

All the same conjugate effects originally refer to the interaction between the C—H bond on the carbon atom and the adjacent bond. A large number of chemically active and electronic spectroscopic data indicate that there is a special p- or -conjugation phenomenon between the propenyl ions and similar alkene carbonyls, namely the so-called conjugation effect:

In the propenyl ion, the p orbital on the olefinic carbon atom partially overlaps with the empty p orbital on the positive carbon ion, while in the analogous ene carbonyl it is the p orbital and alkene of the carbonyl carbon atom. Partial overlap of the p orbitals of carbon atoms