Acid strength: pKa of substituted phenols and ethanolअम्ल सामर्थ्य: प्रतिस्थापित फ़ीनॉलों और एथेनॉल के pKaAcid strength: pKa of substituted phenols and ethanol
NCERT Table 7.3 · Class 12 Chemistry · Chapter 7 · interactive diagram
Parts and what they mean
- p-Nitrophenol, pKa 7.1 (strongest here) (p-नाइट्रोफ़ीनॉल, pKa 7.1 (यहाँ सबसे प्रबल)) — –NO₂ at para withdraws electrons by resonance and induction; the phenoxide charge spreads onto the nitro oxygens.
- o-Nitrophenol, pKa 7.2 (o-नाइट्रोफ़ीनॉल, pKa 7.2) — Ortho –NO₂ also delocalises the charge by resonance.
- m-Nitrophenol, pKa 8.3 (m-नाइट्रोफ़ीनॉल, pKa 8.3) — From meta the charge cannot reach the NO₂ by resonance — only the inductive effect works, so it is weaker than o/p.
- Phenol, pKa 10.0 (फ़ीनॉल, pKa 10.0) — Reference point. Reacts with aqueous NaOH, unlike alcohols.
- m-Cresol, pKa 10.1 (m-क्रीसॉल, pKa 10.1) — Electron-releasing –CH₃ destabilises phenoxide slightly: cresols are less acidic than phenol.
- o-Cresol, pKa 10.2 (o-क्रीसॉल, pKa 10.2) — Less acidic than phenol.
- p-Cresol, pKa 10.2 (p-क्रीसॉल, pKa 10.2) — Less acidic than phenol.
- Ethanol, pKa 15.9 (weakest) (एथेनॉल, pKa 15.9 (सबसे दुर्बल)) — Ethoxide charge is localised on O and the ethyl group pushes electrons in. 15.9 − 10.0 ≈ 6 → phenol is about a million times more acidic.
- Reading the pKa scale (pKa पैमाना पढ़ना) — pKa = −log Ka. Each unit lower = 10 times stronger acid.
Original diagram drawn by Simple Learning Hub, based on NCERT Table 7.3. Report a mistake