Chemistry · General Principles Of Organic Chemistry · NEET
When two atoms in a single bond have different electronegativity, the shared electrons sit closer to the stronger-pulling atom. This makes one atom slightly negative and the other slightly positive. That small charge then pulls a little on the next bond, and so on down the chain. This chain of small electron shifts through sigma bonds is the inductive effect. It is always small and never fully moves the electrons.
-I (negative inductive) means the group PULLS electrons toward itself, so it is electron-withdrawing. Examples: -NO2, -CN, -F, -Cl, -COOH. +I (positive inductive) means the group PUSHES electrons away from itself, so it is electron-releasing. Examples: alkyl groups like -CH3, -C2H5, and -O(-), -COO(-). Compare everything to a hydrogen atom, which is taken as the zero reference.
It is permanent. The inductive effect exists in the ground state of the molecule all the time because it comes only from the difference in electronegativity of atoms already present. This is different from the electromeric effect, which is temporary and appears only when an attacking reagent comes near.
Each bond only passes a fraction of the charge to the next bond, so the polarity gets weaker at every step. NCERT says the magnitude diminishes as the number of intervening bonds increases. After about three carbon atoms it is almost gone. So a -Cl on carbon-1 strongly affects carbon-1, weakly affects carbon-2, and barely affects carbon-3.
The -I effect increases with the electronegativity of the attached atom. Fluorine is more electronegative than oxygen, which is more electronegative than nitrogen (N < O < F). So the -I order is -NH2 < -OR < -F. This was tested directly in NEET 2018.
A -I (electron-withdrawing) group near -COOH pulls electron density away and spreads out the negative charge of the carboxylate ion after the H+ leaves. A more stable carboxylate means a stronger acid. A +I group (like -CH3) does the opposite: it pushes electrons in, destabilises the carboxylate, and makes a weaker acid. That is why HCOOH (no alkyl) is stronger than CH3COOH.
The correct order of decreasing acidity of the following aliphatic acids is:
Which of the following is correct with respect to the -I effect of the substituents? (R = alkyl)
The correct order of strengths of three carboxylic acids, where an electron-withdrawing ring oxygen sits at different distances from the -COOH group, is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. It only shifts the shared electrons slightly, creating small partial charges (delta plus and delta minus). The electrons are never completely handed over, unlike the electromeric effect.
The electromeric effect is stronger. When the two act in opposite directions, NCERT says the electromeric effect predominates because it is a full, temporary transfer of a pi electron pair triggered by an attacking reagent.
Neither. Hydrogen is the reference (zero) point. A group is called +I if it releases electrons compared to H, and -I if it withdraws electrons compared to H.
Through sigma (single) bonds. It travels along the chain of single bonds. Effects that travel through pi bonds and lone pairs are called resonance or mesomeric effects instead.
