Which phenol gives up its proton most easily?
"Which phenol gives up its proton most easily?" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the lesson "Acidity of alcohols and phenols" in Alcohols, Phenols and Ethers. Choose no group, a methyl group or a nitro group, and choose where it sits relative to –OH. Every pKa shown is from NCERT's Table 7.3. Red dots mark where phenoxide's negative charge is spread by resonance. Phenol (10.0) is about 7.9 × 10⁵ times as acidic as ethanol (15.9) because phenoxide spreads its charge over the ring. Electron-withdrawing –NO₂ lowers pKa, most from ortho and para; electron-releasing –CH₃ raises it. JEE Main asked 34 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Acidity of alcohols and phenols in Alcohols, Phenols and Ethers. Change the values and watch what happens.
In JEE Main
42 shifts analysed
34 questions from Alcohols, Phenols and Ethers across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §7.4.4
- Alcohols and phenols release hydrogen gas with reactive metals such as sodium, potassium and aluminium, forming alkoxides and phenoxides. Phenols also react with aqueous sodium hydroxide; alcohols do not.
- The polar O–H bond makes alcohols weak Brönsted acids. An alkyl group pushes electron density towards oxygen (+I), which strengthens the O–H bond and destabilises the alkoxide, so acidity runs primary > secondary > tertiary.
- Alcohols are weaker acids than water: water displaces the alcohol from an alkoxide, and the alkoxide is the stronger base. Sodium ethoxide is a stronger base than sodium hydroxide.
- Through the lone pairs on oxygen, alcohols also act as Brönsted bases and accept a proton from strong acids.
- Phenol is more acidic than an alcohol. The –OH is on an electron-withdrawing sp² carbon, and the negative charge of phenoxide is spread over the ring by resonance, which makes the ion more stable than phenol itself.
- Table values of pKa: o-nitrophenol 7.2, m-nitrophenol 8.3, p-nitrophenol 7.1, phenol 10.0, o-cresol 10.2, m-cresol 10.1, p-cresol 10.2, ethanol 15.9. A larger pKa means a weaker acid.
- Phenol (pKa 10.0) is roughly a million times as acidic as ethanol (pKa 15.9): the pKa gap of 5.9 is a factor of about 7.9 × 10⁵ in Ka.
- An electron-withdrawing group such as –NO₂ raises the acidity of phenol, most strongly from the ortho and para positions where it delocalises the charge. An electron-releasing alkyl group, as in the cresols, lowers it.
- Worked order, most acidic first: 2,4,6-trinitrophenol > 3,5-dinitrophenol > 3-nitrophenol > phenol > 4-methylphenol > propan-1-ol.
Questions
3 answers
- What does the "Which phenol gives up its proton most easily?" simulation show?
- Choose no group, a methyl group or a nitro group, and choose where it sits relative to –OH. Every pKa shown is from NCERT's Table 7.3. Red dots mark where phenoxide's negative charge is spread by resonance.
- Does JEE Main ask questions from Alcohols, Phenols and Ethers?
- Yes. JEE Main asked 34 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Acidity of alcohols and phenols" in Alcohols, Phenols and Ethers (Class 12 Chemistry).
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