Organic Chemistry Basics: Inductive Effect

Fundamental of Organic Chemistry

Inductive Effect

• The permanent displacement of shared pairs of electrons in a carbon chain towards a more electronegative atom is called inductive effect.
• Characteristics:
  • Takes place in a single covalent bond.
  • Occurs in presence of a more electronegative atom.
  • It is an irreversible process.
  • It is a permanent process.
  • As the distance from the electronegative atom increases, the displacement of electron decreases.

Types of Inductive Effect

• +ve inductive effect (+I effect): If an atom or a group having less electronegativity is linked with carbon atom, it donates a electron towards carbon atom.
  • Examples: Alkyl groups, -OH, -NH2, R-O-R, etc.
• -ve inductive effect (-I effect): If an atom or a group having more electronegativity is linked with carbon atom, it withdraws electron from carbon atom.
  • Examples: -NO2, -CHO, -COOH, Halogens (F > Cl > Br > I)

Resonance

• When the properties of a compound cannot be explained completely by a single structure, but can be explained by two or more structures which differ on the movement of electrons (π electron or lone electron), then these structures are called resonating structures or canonical structures and the phenomenon is called resonance.
• Resonance hybrid is more stable than resonating structures.
• Conditions of Resonance:
  • Some atomic skeleton
  • Resonance involves only the movement of electrons from one point to other while the position of atoms remains constant

Examples of Resonance

• CH2=CH-Cl CH2-CH-Cl (vinyl chloride)
• CH3-C=CH-C-OC2H5 CH3-C=CH-C-OC2H5 (Keto form) CH3-C=CH-C-OC2H5 (Enol form)
• CH3COOH CH3-COO- (Acetic acid) CH3-COO (Acetate ion)

Mesomeric Effect

• If an atom or a group is linked with a carbon atom in a conjugated system, it affects the electron density of the conjugated system.
• Examples: -CHO attached to benzene ring

Effects of Resonance

• Resonance is responsible for greater stability of molecules.
• In a resonating hybrid, the bond length is smaller than in conical structures.
• In account of greater stability of resonance hybrid, the reactivity of molecules decreases.

Strength of Acid

• A chemical substance which can donate a proton is said to be an acid.
• The strength of an acid depends on the inductive effect of the substituent group.
• -I effect increases the strength of acid, while +I effect decreases the strength of acid.

Examples of Acid Strength

• Chloroacetic acid (CH2ClCOOH) is stronger than acetic acid (CH3COOH) due to the -I effect of Cl.
• Formic acid (HCOOH) is stronger than acetic acid (CH3COOH) due to the absence of +I effect.

Reactivity of Alkyl Halide

• In alkyl halides, the reactivity order is 3° > 2° > 1°.

Basic Nature of Amines

• A chemical substance which can accept a proton is said to be a base.
• The order of basicity is 2° > 1° > 3°.
• Greater the electron density on N atom, greater is the basic nature.

Steric Hindrance

• In case of 3° amines, the bulky nature of alkyl groups causes steric hindrance, which decreases the basic nature.

Dipole Moment

• More is the inductive effect, more will be the dipole moment.
• Examples: CH₃→I, CH₃→Br, CH₃→Cl

Learn about the fundamentals of organic chemistry, including the inductive effect, electronegativity, and covalent bonds. Understand how replacing hydrogen atoms with more electronegative atoms affects the shared pair of electrons.