Electronic effect and their applications .pptx

The concept of electronic effects plays a crucial role in understanding chemical reactivity, bonding, and the behavior of molecules in various contexts, especially in organic and inorganic chemistry. Electronic effects refer to the influence of the electron distribution within atoms, molecules, or ions on their physical and chemical properties. These effects arise from the intrinsic electronic structure of the molecule, such as the arrangement of electrons in the atomic orbitals, as well as how these electrons interact with surrounding atoms or functional groups. Broadly, electronic effects can be categorized into inductive effects, resonance effects, and hyperconjugation, each contributing to the stability and reactivity of molecules.

The inductive effect is a consequence of the electronegativity differences between atoms in a molecule. When atoms in a bond differ in their ability to attract electrons, it causes a shift in electron density along the bond. This leads to a polarization of the molecule and can stabilize or destabilize certain regions. In organic molecules, this effect is particularly notable in determining the strength of acids and bases, as it affects the distribution of charges across the molecule. Functional groups that are more electronegative withdraw electron density, making certain sites more positively charged, while electron-donating groups push electron density, influencing the overall reactivity of the molecule.

Resonance effects come into play when a molecule can be represented by two or more valid Lewis structures, called resonance structures. These structures describe the delocalization of electrons, typically π-electrons, over a conjugated system or between atoms. Resonance leads to stabilization as the actual electron distribution is a hybrid of these structures, resulting in lower energy and enhanced stability. This effect is significant in aromatic compounds like benzene, where resonance contributes to the stability and unique chemical properties of these systems.

1. CHEMISTRY ASSIGNMENT ELECTRONIC EFFECT AND THEIR APPLICATIONS SUBMITTED TO – DR. MANMOHAN SIR SUBMITTED BY – MR. MAYANK KUMAWAT

2. ELECTRONIC EFFECT The effect of electrons that are located in the chemical bonds within the atoms of the molecule is termed an electronic effect. The electronic effect is also explained as the effect through which the reactivity of the compound in one portion is controlled by the electron repulsion or attraction producing in another portion of the molecule. An electronic effect impacts the reactivity, properties, and structure of the compound. The relation between the electronic structure and geometry of the compound can also be emphasized by the term ‘stereo electronic effect’. The electromeric effect is a molecular polarizability occurring by an intramolecular electron displacement characterized by the substitution of one electron pair for another within the same atomic octet of electrons. It is sometimes called the conjugative mechanism, and previously, the tautomeric mechanism).

3. TypeS of ELECTRONIC EFFECT The Inductive Effect. Resonance. The Mesomeric Effect. Electromeric Effect. Hyperconjugation.

4. 1. INDUCTIVE EFFECT When an electron-releasing or an electron-withdrawing species is introduced to a chain of atoms (generally a carbon chain), the corresponding negative or positive charge is relayed through the  carbon chain  by the atoms belonging to it. This causes a permanent dipole to arise in the molecule and is referred to as the inductive effect.

5. Inductive Effect on Acidity and Basicity :- Using the inductive effect, we can predict the acidity and basicity of compounds. As a generalisation, it may be said that the electron-withdrawing groups (EWG) increase the acidity of a compound, and the electron-donating group decrease the  acidity of a compound . This is because, if we take the conjugate base of the acid, that is, RCOO-, if R is electron-withdrawing, then the conjugate base is stabilised via delocalisation of the formed negative charge. If R had been electron-donating, then the conjugate base would have been destabilised because of inter-electronic repulsions. For example , formic acid (HCOOH) is more acidic than  acetic acid (CH3COOH)  due to the +I inductive effect of the methyl group attached to the carboxylic acid group.

6. TYPES OF INDUCTIVE EFFECT :- Negative inductive effect or -I effect Positive inductive effect +I effect -I Effect (Negative Inductive Effect) When an  electronegative atom , such as a halogen, is introduced to a chain of atoms (generally, carbon atoms), the resulting unequal sharing of electrons generates a positive charge which is transmitted through the chain. This causes a permanent dipole to arise in the molecule wherein the electronegative atom holds a negative charge, and the corresponding effect is called the electron-withdrawing inductive effect or the -I effect. +I Effect (Positive Inductive Effect) When a chemical species with the tendency to release or donate electrons, such as an  alkyl group , is introduced to a carbon chain, the charge is relayed through the chain, and this effect is called the positive inductive effect or the +I effect.

7. 2 . RESONANCE The polarity induced in a molecule by the interaction of a lone pair of electrons with a pi bond or the interaction of two pi bonds in nearby atoms is known as the resonance effect. The withdrawal effect or releasing effect of electrons attributed to a particular substituent through the delocalization of π or pi-electrons that can be seen by drawing various canonical structures is called a resonance effect or mesomeric effect. M or R symbols are used to represent the resonance effect.

8. Types Of Resonance Effects :- Positive Resonance Effect Negative Resonance Effect Positive Resonance Effect-   Positive resonance effect occurs when the groups release electrons to the other molecules by the process of delocalization. The groups are usually denoted by +R or +M. In this process, the molecular  electron  density increases. For example- -OH, -SH, -OR,-SR. Negative Resonance Effect-   Negative resonance effect occurs when the groups withdraw the electrons from other molecules by the process of delocalization. The groups are usually denoted by -R or -M. In this process, the molecular electron density is said to decrease. For example- -NO2, C=O, -COOH, -C≡N.

9. 3. The Mesomeric Effect The polarity developed between atoms of a conjugated system by the electron transfer or pi–bond electron transfer is known as the Mesomeric effect. In simple terms, we can describe mesomeric effect occurs when π electrons move away from or towards a substituent group in a conjugated orbital system.

10. TYPES OF MESOMERIC EFFECT :- +M effect -M effect +M effect (Positive mesomeric effect) When the electrons or the pi electrons are transferred from a particular group towards a conjugate system, thus increasing the electron density of the conjugated system then such a phenomenon is known as (+M) effect or positive mesomeric effect. For the +M effect, the group should have either a lone pair of electrons or should have a negative charge. The +M effect gives negative charge to the conjugate system or it can be said that the electron density increases on the conjugate system due to this. These conjugate systems show more reactivity towards electrophiles and less reactivity towards a nucleophile.

11. Group showing +M effect –NH, –NH 2 ,–NHR, –NR 2 , – O, – OH, –OR, – F, – Cl, –O–COR, – NHCOR, –SH, – SR etc -M EFFECT (NEGATIVE MESOMERIC EFFECT) When the pi-bond electrons are transferred from the conjugate system to a particular group thus the electron density of the conjugate system is decreased, then this phenomenon is known as negative mesomeric (–M) effect. For –M effect, the group should have either a positive charge or should have a vacant orbital. –M effect makes the compound more reactive towards a nucleophile as it decreases the electron density in the conjugate system and at the same time it is less reactive towards electrophile due to same reasons. The group which shows –M effect include; –NO 2 , –CN, –COX, –SO 3 H, – CHO, –CONH 2 , –COR, –COOH, –COOR etc. SIGNIFICANCE OF MESOMERIC EFFECT It describes the distribution of the charge in the compound, helps to decide the point at which electrophiles or nucleophiles attack. Useful in describing physical characteristics such as dipole moment, bond length.

12. 4. Electromeric Effect The instantaneous formation of a dipole in the molecule of an organic compound due to the complete transfer of shared pi  electron  pairs to one of the atoms under the influence of an attacking reagent is referred to as the Electromeric effect. This effect can be observed in organic compounds that contain at least one multiple bond. When the atoms participating in this multiple bond come under the influence of an attacking reagent, one pi bonding pair of electrons is completely transferred to one of the two atoms. The electromeric effect is a temporary effect that remains as long as the attacking reagent is present and exposed to the organic compound. Once this attacking reagent is removed from the system, the molecule that was polarized goes back to its original state.

13. TYPES OF ELECTROMERIC EFFECTS +E Effect -E Effect +E Effect This effect occurs when the electron pair of the pi bond is moved towards the attacking reagent. The +E effect can be observed in the addition of acid to alkenes. The attacking reagent attaches itself to the atom which obtained an electron pair in the transfer. The +E effect is generally observed when the attacking reagent is an electrophile and the pi electrons are transferred towards the positively charged atom. -E Effect This effect occurs when the electron pair of the pi bond is moved away from the attacking reagent. The attacking reagent attaches itself to the positively charged atom in the molecule, i.e. the atom which lost the electron pair in the transfer. The -E effect is generally observed when the attacking reagent is a nucleophile and the pi electrons are transferred to the atom which the attacking reagent will not bond with .

14. 5. Hyperconjugation Hyperconjugation effect is a permanent effect in which localization of σ electrons of C-H bond of an alkyl group directly attached to an atom of the unsaturated system or to an atom with an unshared p orbital takes place.

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