Conjugate effect introduction

- Mar 24, 2018 -

"The conjugate effect is stable" is one of the most basic principles of organic chemistry.

Conjugation effect

Conjugation effect

However, since the 1930s, the average bond length, the 4N+2 aromaticity theory, the cause of the benzene ring D6h structure, the causality of the molecular conformation and conjugation effect, and the structural effect of the π-electron delocalization have been extensively studied. Questioned. Among them, the most notable is that Vollhardt et al. synthesized a benzene-based compound having a cyclopentatriene geometric feature in the center benzene ring, and Stanger et al. synthesized a benzo-based derivative having a bond length averaged from 0.143 to 0.148 nm in length. . (1999) Stanger again obtained a benzo-type compound having a single bond length in the benzene ring. In the field of theoretical calculation, the controversy is mainly expressed in the calculation method, focusing on how to break down the action energy into two parts, π and σ. With the development of the controversy, the application of the action energy decomposition method in organic chemistry is continuously developing and improving. Hückel The absolute authority of theories in organic chemistry has also been challenged. For this reason, the history of the development of energy-splitting methods was briefly introduced, and the rationality of the Kollma method was questioned. In addition, our new energy-decomposition method was specifically introduced, and New viewpoints and new modes of thinking in the study of conjugate effects and aromaticity. [2]

Normal conjugate effect

Also called π-π conjugate. It refers to the dissociation of π electrons that occurs when more than two double bonds (or triple bonds) are linked by a single bond.

Conjugation effect

Conjugation effect

C.K. Ingold calls this effect an intermediate 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). The greater the electronegativity of the Y atom and its p-orbital radius, the greater its ability to attract π electrons, and the more conducive the conjugated effect of the group -X=Y attracting π electrons from the reference double bond A=B-. (As shown by the arrow on the right). In contrast, if the electronegativity of the A atom and its p-orbital radius are greater, the smaller its ability to release π electrons to move to the Y atom, the less favorable it is to electrons toward the -X=Y group. Conjugate effect. The properties of the intermediate atoms B and X are also directly related to the conjugate effect. The multiple electron conjugate effect is also called 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 for the case where Z can form a d-π conjugate, there is a conjugate effect of electron donation to the reference double bond A=B-direction. The pair of p electrons of the Z atom acts like the -X=Y group in a normal conjugated system. [2]

Hyperconjugation effect

Also known as σ-π conjugate. It is composed of an alkyl C-H bond with the σ bond electrons and adjacent

Conjugation effect

Conjugation effect

A semi-full or full-empty p orbit overlaps each other resulting in a conjugate phenomenon. According to the theory of multiple electron conjugates, one C—H bond or the entire CH3 group can be viewed as a pseudo-atom. 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 α-H atoms in the alkyl group. The methyl group is the strongest and the tertiary butyl group is the weakest. The hyperconjugation effect is much weaker than the normal normal conjugation effect and the multiple electron conjugation effect. [2]

Conjugate effect

It is also called that the p orbit overlaps with the p orbital σ type. Methyl groups above the methyl group, in addition to hyperconjugation effects, may also produce

Conjugation effect

Conjugation effect

Same as conjugate effect. All the same conjugate effects originally refer to the interaction between the C-H bond on the beta carbon atom and the adjacent pi bond. A large number of chemically active and electronic spectroscopic data indicate that there are special p-π or π-π conjugates in the propenyl-like and similar alkenyl groups, the so-called conjugation effect:[3]

In the propenyl ion, the p orbital on the ene carbon atom partially overlaps with the empty p orbital on the positive carbon ion (β) for σ type, and in the similar ene carbonyl group, the p orbital of the carbonyl carbon atom. Partial overlap of the p orbitals of the olefinic carbon atoms (β) for σ: This conjugate effect has less effect than the hyperconjugation effect. The entire conjugation effect between alkyl and alkene chains should include hyperconjugation and conjugation effects. [2]

D-p conjugate

Also known as d orbital conjugate. A conjugate phenomenon that occurs when the p orbital of an atom overlaps with the d orbital of another atom, such as the dp conjugate in an organosilicon compound structure; here, a part of the π electron cloud on the benzene ring enters the 3d of the silicon The orbits form dp conjugates, making the silicon atoms more firmly bonded to the benzene ring. In addition, the conjugate effect is divided into two categories: static and dynamic. The static conjugate effect exists in the unreacted conjugated molecule, which is the result of the highly mobile π electrons in the conjugated molecule and the displacement of π electrons. The dynamic conjugate effect refers to a conjugate phenomenon caused by the redistribution of the π-electron density in the conjugated system due to the action of offensive agents at the instant of the chemical reaction