Chemistry · Chemical Bonding · NEET
No. This is the biggest mistake. The molecule does NOT spend some time in structure I and some time in structure II. It stays in ONE fixed structure the whole time, the resonance hybrid. The separate canonical forms are only drawings we use because one Lewis structure cannot show the truth. NCERT says clearly: the molecule does not exist for a fraction of time in one form and other fractions in another.
No, they have no real existence. Each canonical form is imaginary. You draw them only to help describe the real molecule. For example, in ozone (O3) you draw two forms with one single and one double bond, but really both O-O bonds are equal (128 pm, in between single 148 pm and double 121 pm). Neither drawn form is the truth; the hybrid is.
In resonance the canonical forms are imaginary and there is NO equilibrium between them; only nuclei stay fixed and electrons are shown differently. In tautomerism (like keto and enol forms), both forms are REAL molecules, atoms (usually an H) actually move, and there is a real chemical equilibrium (double arrow ⇌) that can be measured. Resonance = one blended structure; tautomerism = two real molecules interconverting.
No. In resonance the positions of the nuclei (atoms) stay exactly the same in every canonical form. Only the placement of bonding and non-bonding electron pairs is shown differently. In tautomerism, a real atom (a proton) actually shifts position, so atoms DO move there. That is a key way to tell them apart.
The double-headed arrow (↔) only means the structures on both sides together describe ONE molecule, the hybrid. It does NOT mean equilibrium and it does NOT mean the molecule is turning into the other form. Do not confuse it with the equilibrium arrow (⇌) used in tautomerism, which does mean two real forms are interconverting.
Because a single Lewis structure cannot correctly show a molecule where all bonds are equal, like CO3^2- or O3. Drawing several canonical forms and blending them into the hybrid lets us represent the real, averaged bonding. Resonance also stabilises the molecule: the hybrid has LOWER energy than any single canonical form, and this lowering is the resonance energy.
Identify the correct statement.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. Resonance is not a process and nothing is moving between forms. The molecule simply has one real hybrid structure. 'Resonance' is just the name for the method of using several imaginary canonical forms to describe that one real structure.
Only tautomerism. Tautomers (like keto and enol) are two real molecules in a genuine equilibrium (⇌). Resonance forms are imaginary and have no equilibrium.
No. In resonance only electrons are shown differently; the nuclei stay fixed. In tautomerism an atom (usually H) actually shifts, so the atomic positions change.
The energy of the resonance hybrid is lower than the energy of any single canonical form. This extra stability is called resonance energy, and it means the molecule is harder to break apart than any single drawn structure suggests.
A single double-headed arrow (↔) is placed between canonical forms. Never use the equilibrium arrow (⇌); that one is only for tautomerism and other real equilibria.
