313_Chemistry_Eng_Lesson26.pdf). Content covers sections 26.1–26.3.Compounds with C–O single bonds: alcohols (ROH), phenols (ArOH) and ethers (ROR′). They are central in industry (ethanol, phenol, bakelite) and synthesis. This lesson covers classification, IUPAC names, preparation, H-bonding, reactions (including Lucas test and dehydration), phenol acidity and electrophilic reactions, and ether synthesis (Williamson) and cleavage.
1°: RCH₂OH · 2°: R₂CHOH · 3°: R₃COH. IUPAC: parent + -ol with lowest number for OH (propan-1-ol, propan-2-ol, 2-methylpropan-2-ol).
Preparation: (1) RX + aq KOH/NaOH. (2) Alkene hydration — acid-catalysed (Markovnikov); oxymercuration–demercuration; hydroboration–oxidation (anti-Markovnikov). (3) Reduction of carbonyls — aldehydes/acids/esters → 1° alcohols; ketones → 2° (NaBH₄, LiAlH₄, H₂/Pd).
Physical: O–H H-bonding raises b.p. and water solubility of lower alcohols. Methanol/ethanol fully miscible; higher homologues less so.
Acid–base: Weak acids (pKₐ ~15–16) — NaH or Na metal → alkoxide. Also weak bases — protonated by strong acids to ROH₂⁺.
→ Alkyl halides: HX, PBr₃, SOCl₂ (gases by-product). 3° react readily with HCl; 1°/2° prefer PBr₃/SOCl₂.
Lucas test: anhyd. ZnCl₂ + conc. HCl — turbidity: 3° immediate, 2° within minutes, 1° none (or very slow).
Dehydration: H₂SO₄/H₃PO₄ — ease 3°>2°>1°; E1 via carbocation. ~413 K intermolecular → ether; higher T → alkene.
Oxidation: 1° → aldehyde → carboxylic acid (strong oxidant); 2° → ketone; 3° resistant (no H on carbinol C). Controlled oxidation of 1° with PCC etc. stops at aldehyde (higher level).
Uses: fuels, solvents, beverages (ethanol), antifreeze, synthesis of RX, alkenes, esters.
OH attached to aromatic ring. Disinfectant; precursor to aspirin, bakelite, dyes. Names: phenol, o/m/p-cresol, nitrophenols, catechol, resorcinol, hydroquinone, naphthols.
Preparation: (1) ArN₂⁺ hydrolysis (mild, general). (2) Alkali fusion of sodium benzenesulphonate. (3) Dow: PhCl + aq NaOH, high T/P. (4) Cumene: benzene + propene → cumene → air oxidation → acid → phenol + acetone (main industrial route).
Acidity: much stronger than alcohols — phenoxide resonance. e⁻-withdrawing groups (especially o/p–NO₂) increase acidity (picric acid very strong). e⁻-donating alkyls slightly decrease acidity.
Reactions: NaOH → sodium phenoxide; FeCl₃ violet complex (test); Br₂ water → 2,4,6-tribromophenol white ppt (ring highly activated); nitration; Kolbe–Schmitt (CO₂ → salicylic acid); Reimer–Tiemann (CHCl₃/NaOH → salicylaldehyde); azo coupling with ArN₂⁺ → dyes. Electrophilic substitution is o/p-directed and faster than benzene.
R–O–R′ (alkyl/aryl). Symmetrical (diethyl ether) or unsymmetrical (ethyl methyl ether). Cyclic ethers (THF) are solvents. IUPAC: larger group as parent alkane, smaller as alkoxy (methoxyethane).
Preparation: intermolecular dehydration of alcohols (lower T than alkene formation); Williamson: RONa + primary R′X → ROR′ (SN2; 3° R′X fails → elimination).
Structure: bent like water; polar C–O; no H on O → no intermolecular H-bonds between ether molecules → lower b.p. than isomeric alcohols; good polar solvents.
Reactions: generally unreactive (hence solvents). Autoxidation → explosive peroxides (store carefully). Protonated by strong acids (oxonium). Cleavage with hot HI/HBr: ROR + HI → ROH + RI then further to 2 RI; Nu attacks less hindered alkyl group in unsymmetrical ethers.
Uses: diethyl ether as solvent and (historically) anaesthetic; THF solvent; MTBE fuel additive (context-dependent).
High-yield: 1°/2°/3° classification; hydration methods and anti-M hydroboration; Lucas; dehydration T control; oxidation products; phenol acidity reason; cumene process; Br₂/FeCl₃ tests; Williamson constraints; ether vs alcohol b.p.; HI cleavage.
Links L25 (ROH→RX, SN2) and L24 (alkene hydration). Next: aldehydes, ketones, carboxylic acids (L27) — oxidation of alcohols feeds those chapters.
Most exam-important points from this chapter:
1°/2°/3° by structure. Prep: RX, hydration (M/anti-M), carbonyl reduction. Lucas, dehydration T, oxidation products.
H-bonding → high b.p. & water solubility. Weak acids; form alkoxides with Na.
More acidic than alcohols (resonance). Cumene/Dow/diazonium prep. Br₂, FeCl₃, Kolbe, Reimer–Tiemann, azo dyes.
Williamson with 1° R′X. Polar solvents; no intermolecular H-bonds. HI cleavage; peroxide hazard.
ROH→RX (L25) · alkenes (L24) · oxidation → carbonyls (L27).
Extracted from NIOS Chemistry (313) board exam papers in your PDF. Chapter L26 — Alcohols, Phenols and Ethers only. Use Model Answer for marking points; Explanation for concept clarity.
3 question(s) · Sources: 313/MAY/205C, 313/TUS/105A
PYQ1. Hemiacetals are chemically — (A) alkoxy alcohols (B) alkyl alcohols (C) gem-dialkoxy compounds (D) ethylene glycol ho‘rEogrQ>¡b amgm¶{
Model Answer
Model approach (select the best option):
Eliminate options that contradict definitions/equations from the chapter notes. NIOS awards full mark for the single correct choice.
Explanation
This MCQ belongs to L26. Recall the core definition or formula from notes, then match it to one option. Paper: 313/TUS/105A · Q12.
Tip: For numerical MCQs, write the formula first, substitute values, then pick the option.
PYQ2. Read the passage given below and answer the following questions (out of four attempt any two) : Ethers are organic compounds in which an oxygen atom is bonded to two alkyl groups or aryl groups. Ethers have geometry similar to water and alcohols. Draw the geometry of an ether molecule. Illustrate the basic nature of ethers with the help of a suitable reaction. What is the IUPAC name of methyl propyl ether? How can ethers be prepared by Williamson’s synthesis? Illustrate with an example.
Model Answer
State the precise definition from the L26 notes in 1–2 sentences, include formula/example if marks ≥ 2, and avoid extra theory beyond the ask.
Explanation
Definition questions score for accuracy of wording + one supporting point/example. Do not write full chapter summaries.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/TUS/105A · Q25 · 2 mark(s) · L26.
PYQ3. Why is the purification of final product not required when ethanol reacts with thionyl chloride? Also, give the chemical equation for the reaction. O~ EWoZm°b, Wm¶mo{Zb ³bmoamBS> Ho$ gmW A{^{H«$¶m
Model Answer
Give the chemical reason linked to structure/bonding/equilibrium. Start with the principle, then apply to the species named in the question.
Explanation
Reasoning marks require principle + application. Cite electron effects, stability, or Le Chatelier as relevant.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205C · Q36 · 2 mark(s) · L26.
Six problems spanning this chapter’s NIOS syllabus. Every question is built from the notes and formula sheet: solve with equations first, then read the formal textbook-style write-up, the easy explanation, and the topic in depth (formulas, meaning, exam tips). If the question says draw, a labelled pencil sketch is provided. Explanations open by default.
Classify alcohols as 1°, 2°, 3° with one example each.
Final answer: 1°/2°/3° by C bearing OH
Based on number of carbons attached to carbinol carbon.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Count how many C stick to the C–OH carbon.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Affects oxidation and Lucas test.
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
How is ethanol manufactured from ethene industrially?
Final answer: Hydration of ethene
Electrophilic addition of water across C=C.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Add water across the double bond with acid catalyst.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Fermentation is biological route to ethanol.
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Why is phenol more acidic than ethanol?
Final answer: Resonance stabilisation of phenoxide
Delocalisation of negative charge on phenoxide ion.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
After losing H⁺, charge spreads into the ring—more stable.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Electron-withdrawing groups increase phenol acidity.
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Outline Williamson ether synthesis.
Final answer: RO⁻ + R′X → ROR′
Classic SN2 route to unsymmetrical ethers.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Salt of alcohol attacks alkyl halide to make ether.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Avoid 3° RX (elimination).
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What does Lucas test distinguish?
Final answer: Alcohol class by turbidity rate
3° react fastest via SN1.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Cloudiness appears quickest for tertiary alcohols.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Room temperature vs heat conditions matter.
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What does acidic KMnO₄ do to primary alcohol (complete)?
Final answer: 1° → carboxylic acid
Strong oxidants convert 1° alcohols to acids.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Chop all the way to –COOH with strong oxidant.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
PCC can stop at aldehyde.
Linked to chapter notes (L26). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.