Inductive Effect PDF

# Electron Displacement in Organic Compounds ## Introduction When organic compounds are non-polar, the bond pairs of the electrons are present at the center of the nuclei of bonded atoms. However, when the organic compound are polar due to the presence of more electronegative atoms or groups, then...

# Electron Displacement in Organic Compounds ## Introduction When organic compounds are non-polar, the bond pairs of the electrons are present at the center of the nuclei of bonded atoms. However, when the organic compound are polar due to the presence of more electronegative atoms or groups, then the bond pair of electrons are shifted towards the more electronegative group. This is known as electronic displacement of organic compounds. There are four types of electron displacement: - Inductive / Electromeric Effect - Resonance / Mesomeric Effect - Electromeric Effect - Inductomeric Effect Out of these, Inductive Effect and Resonance Effect are permanent effects, while Electromeric Effect and Inductomeric Effect are temporary. ## Inductive Effect or I-Effect The permanent displacement of shared pair of electrons or bond pair electrons in a C-chain towards the more electronegative atom or group is called inductive effect. - It is indicated by middle aeradline. ### Types of I-Effect: - **Negative Inductive Effect (-I Effect)** - When More electronegative atom or group (Electron withdrawing Group) present in a C-chain, the shared pair of electrons are shifted towards that group, and this is known as -I effect. - Example: C - C - C - Cl - Here, partial -ve charge is developed in X-atom (Halogen) and + partial +ve charge is developed on C1, C2, C3 and Cl respectively. - **The group producing -I effect in decreasing order as:** - -NF3>-NR3 > -NH3 > -NO2> -SOR > -CN > -C = O > -C-OH > -C-H > -F > -Cl > -Br > -I > -OC6H5 > -COOR >-H - -OR > -OH > = C = CH2 > NH2 > C6H5 (ph) > -CH = CH2 > -CH3 - **Positive Inductive Effect or +I Effect:** - When "Electron Donating Group" is present in the Carbon chain, then the shared pair electrons are directed towards C-chain, then it is known as +I effect. - Example: SSS - 88 - 8 - The group producing +I effect, in the decreasing order: -O-> -COO -> -CR3> -CHR2> -CH2R > -CH3 > H ## Characteristics of Inductive Effect: 1. It takes place in polar organic molecule having more or less electronegative atoms or groups and bonded with single covalent bond. 2. It is permanent and irreversible effect. 3. It produces bond polarization. 4. The displacement of shared electron pairs along a C-chain decreases upto third C-atom from the C-atom bearing more or less electronegative atom or group, then it vanishes. 5. The displaced electron pair doesn't leave the overlapping orbitals, but only the orbital is deformed a little. 6. Different group produce different I-effect. ## Applications of I-Effect: ### 1. Bond Length: Inductive effect decreases the bond length due to the result of ionic nature in bond. - More is the I-effect, lesser is the bond length order and - - Example: R-X bond length order are - R-F < R-Cl < R-Br < R-I - Decreasing order of bond length Increasing order of I-effect ### 2. Dipole Moment: I-effect increases the dipole moment of a molecule - Dipole moment = qD - q = Charge, D= distance between separated pole - Charge developed due to I-effect - Example: The dipole moment of alkyl halides on the basis of I-effect - R-F > R-Cl > R-Br > R-I - But experimentally, - R-Cl > R-F > R-Br > R-I - Distance factor: ↑ - Charge factor: ↓ - To explain the above order, R-F and R-Cl distance factor is dominant, and next in R-Br and R-I, charge factor is dominant. ### 3. Reactivity: Inductive effect increases reactivity of compounds. More the -I effect, more its reactivity. Thus., the reactivity of CH3 - Cl is more than CH3Br. ### 4. Strength of Acid and Base: - The power of an acid to give proton (H+) is called strength of acid. More the power of to donate the proton, more is the strength of acid. - The presence of group producing -I effect increases acidic strength and the group producing +I effect decreases acidic strength - **Example:** - **Relative strength of Monoacitic acid ** - Formic Acid is stronger acid than Acetic Acid. - **Ans:** H - C - OH (Formic Acid) Strongere acid - CH3 - C - OH (Acetic Acid) Weaker acid - It is because methyl group in acetic acid produces +I effect. Thus, H+ ion formed by acetate, ion is destabilized by electron releasing CH3 group, but in case of Formic acid, there is no any I effect so, formate ion is more stable. - **Chloroacetic acid is more stronger than acetic acid.** - CL-CH2-C-OH (Chloroacetic acid) (Strongere acid) - CH3 - C - OH (Acetic acid) (Weaker acid) - Chloroacetic acid is stronger than acetic acid. In chloroacetic acid, the chlorine atom causes -I effect and makes the release of ion easier. - **Dichlorto acetic acid is more stronger than chloroacetic acid.** - CL - CH2- C - OH (Dichlorco acetic acid) (Strong Acid) - CL-CH2-C-OH (chlorcoacetic acid) (weak acid) - Dichlorco acetic acid is stronger than chloroacetic acid. In chloro acetic acid the chlorine atom causes -I effect and makes the release of ion easier. But in dichlorto acetic acid, the two chlorine atom causes more -I effect, and makes the release of ion more easier than a chloroacetic acid. - **Chloroacetic acid is stronger acid than chloro propanoic acid.** - Cl-CH2-C-OH (stronger) - Cl + CH2CH2 - C - OH (weaker) - In chloroacetic acid, chlorine atom produces more -I effect. In chloropropanoic acid chlorine atom produces more -I effect due to less distance, from carboxylic acid but in chloro-Propanoic acid Cl-atom produced less -I effect due to greater distance from carboxylic acid. - **Relative Acid Strength: haloacetic acid**> CH2-C-COOH> CH3-COOH - **Relative Acid Strength: dicarboxylic acids**: - Cl3-C- COOH < Cl2-CH-COOH < CH-COOH < CH2-COOH - COOH <COOH (CH2) 2 COOH < (CH2)3 COOH> (CH2)4 COOH - Oxalic acid< Malonic acid < Succinic acid < Glutaric acid - **(CH2)4 - COOH > (CH2)5 - COOH-** - adiapic acid > Pimetic Acid ### 5. Strength of Base: - Strength of base is the power of donating electron pairs or strength of occupying H+ion. More is the electron donating power or power of the basic strength, presence of group producing +I effect increases basic strength and vice-versa. - **Example:** - Methyl amine is a stronger base than ammonia. - **Ans:** In Methyl amine, CH3 group produces +I effect, so the lone pair of electron on N-atom is more available, and hence easily donate e- pair or accept H+. But, in ammonia, no +I effect is produced, thus the lone pair e- is less available and accept H+ ion less quickly. - **H - C - N - H** - **H + I effect** - **NH3** - **Not + I effect** - **Relative Basic Strength of amine**: R3N > R2NH > RNH2 > NH3