Alcohol & Ether flash cards

1. 1.How are alcohols classified based on the type of carbon bearing the $-\text{OH}$ group?

   Primary (1°): $-\text{OH}$ on carbon attached to one other carbon (e.g. $\text{CH}_3\text{CH}_2\text{OH}$).
   Secondary (2°): on carbon attached to two carbons.
   Tertiary (3°): on carbon attached to three carbons (e.g. $(\text{CH}_3)_3\text{COH}$).

   Hint: Count how many carbons are bonded to the C–OH carbon.

2. 2.Distinguish between allylic, benzylic and vinylic alcohols.

   Allylic: $-\text{OH}$ on carbon adjacent to $\text{C}=\text{C}$ ($\text{CH}_2=\text{CH}-\text{CH}_2\text{OH}$).
   Benzylic: $-\text{OH}$ on carbon attached to benzene ring ($\text{C}_6\text{H}_5\text{CH}_2\text{OH}$).
   Vinylic: $-\text{OH}$ directly on $\text{C}=\text{C}$ carbon — unstable (enol).

   Hint: Position of OH relative to the double bond / ring.

3. 3.What is the difference between an alcohol, a phenol and an ether structurally?

   Alcohol: $-\text{OH}$ on $sp^3$ (aliphatic) carbon.
   Phenol: $-\text{OH}$ directly on aromatic ($sp^2$) ring carbon.
   Ether: $\text{R}-\text{O}-\text{R}'$, oxygen bonded to two carbons, no O–H.

   Hint: Where oxygen and its H sit.

4. 4.Why is the C–O–H bond angle in methanol ($108.9°$) larger than in water ($104.5°$)?

   The bulky methyl group causes greater steric repulsion than the H in water, pushing the angle wider despite lone-pair repulsions on oxygen.

   Hint: Compare $\text{CH}_3$ vs H bulk.

5. 5.State the industrial preparation of methanol from water gas.

   $\text{CO} + 2\text{H}_2 \xrightarrow[200-300\,\text{atm}]{\text{ZnO}/\text{Cr}_2\text{O}_3,\,573\text{K}} \text{CH}_3\text{OH}$. Historically called 'wood spirit' from destructive distillation of wood.

   Hint: Water gas = CO + H₂ over a metal-oxide catalyst.

6. 6.How is industrial ethanol prepared by fermentation of sugar?

   $\text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{zymase}} 2\,\text{C}_2\text{H}_5\text{OH} + 2\,\text{CO}_2$. Sucrose is first hydrolysed by invertase, then glucose is fermented by zymase (both from yeast).

   Hint: Two enzymes: invertase then zymase.

7. 7.Give the acid-catalysed hydration of alkenes to alcohols and its regiochemistry.

   $\text{CH}_3\text{CH}=\text{CH}_2 + \text{H}_2\text{O} \xrightarrow{\text{H}^+} \text{CH}_3\text{CH(OH)CH}_3$. Follows Markovnikov addition (OH to more substituted carbon); proceeds via carbocation, so rearrangements possible.

   Hint: H⁺ makes a carbocation; OH goes Markovnikov.

8. 8.How does oxymercuration–demercuration convert an alkene to an alcohol?

   $\text{Hg(OAc)}_2/\text{H}_2\text{O}$ then $\text{NaBH}_4$. Gives Markovnikov alcohol without rearrangement (no free carbocation, cyclic mercurinium ion).

   Hint: Markovnikov but rearrangement-free.

9. 9.What does hydroboration–oxidation of an alkene give and with what regiochemistry?

   $\text{B}_2\text{H}_6$ then $\text{H}_2\text{O}_2/\text{OH}^-$ gives the anti-Markovnikov, syn-addition alcohol. E.g. propene $\rightarrow$ propan-1-ol.

   Hint: BH adds anti-Markovnikov, syn.

10. 10.How are 1°, 2° and 3° alcohols obtained from carbonyl compounds via Grignard reagents?

    HCHO + RMgX $\rightarrow$ 1° alcohol; other aldehydes $\rightarrow$ 2°; ketones $\rightarrow$ 3°. After addition, hydrolyse the alkoxide with dilute acid.

    Hint: Formaldehyde→1°, aldehyde→2°, ketone→3°.

11. 11.What products form on reduction of an aldehyde and a ketone with $\text{NaBH}_4$ or $\text{LiAlH}_4$?

    Aldehyde $\rightarrow$ 1° alcohol; ketone $\rightarrow$ 2° alcohol. $\text{LiAlH}_4$ also reduces $-\text{COOH}$ and esters to 1° alcohols; $\text{NaBH}_4$ does not.

    Hint: Add H₂ across C=O.

12. 12.How does the hydrolysis of alkyl halides give alcohols and which mechanism is followed?

    $\text{RX} + \text{aq. KOH} \rightarrow \text{ROH}$. 1° via $S_N2$, 3° via $S_N1$. Wet $\text{Ag}_2\text{O}$ can also be used.

    Hint: aq. KOH; substrate decides SN1/SN2.

13. 13.Why do lower alcohols have much higher boiling points than alkanes or ethers of comparable molar mass?

    Alcohols form intermolecular hydrogen bonds via O–H. Ethers and alkanes lack O–H, so no H-bonding — their boiling points are far lower.

    Hint: Look for the O–H that can H-bond.

14. 14.How does the boiling point of alcohols vary within primary isomers, and with branching?

    Boiling point rises with chain length (more surface/van der Waals). Among isomers, more branching lowers the boiling point (smaller surface area). E.g. n-butanol > isobutanol > tert-butanol.

    Hint: Branching = compact = lower b.p.

15. 15.Why are lower alcohols soluble in water but solubility decreases with chain length?

    The $-\text{OH}$ group H-bonds with water. As the hydrophobic hydrocarbon chain grows, it dominates and disrupts H-bonding, so solubility falls.

    Hint: Polar head vs non-polar tail.

16. 16.Why is phenol acidic? Explain with resonance.

    On losing $\text{H}^+$, the phenoxide ion is stabilised by resonance delocalising the negative charge into the ring. Phenol $pK_a \approx 10$, far more acidic than alcohols ($pK_a \approx 16-18$).

    Hint: Stability of phenoxide vs alkoxide.

17. 17.Why are alcohols weaker acids than water?

    Alkyl groups are electron-donating (+I), which intensifies the negative charge on the alkoxide, destabilising it. So $\text{RO}^-$ is less stable than $\text{OH}^-$ and ROH is a weaker acid than water.

    Hint: +I effect destabilises alkoxide.

18. 18.Arrange 1°, 2°, 3° alcohols in order of acidity and explain.

    Acidity: 1° > 2° > 3°. More alkyl groups = stronger +I effect = more destabilised alkoxide = weaker acid. tert-butanol is the least acidic.

    Hint: More +I groups → weaker acid.

19. 19.How do electron-withdrawing and electron-donating substituents affect phenol acidity?

    EWG (e.g. $-\text{NO}_2$, esp. o/p) increase acidity by stabilising phenoxide; EDG (e.g. $-\text{CH}_3$, $-\text{OCH}_3$) decrease it. Thus picric acid (2,4,6-trinitrophenol) is very acidic.

    Hint: EWG stabilises the negative charge.

20. 20.Arrange in increasing acidity: phenol, ethanol, water, carbonic acid.

    $\text{C}_2\text{H}_5\text{OH} < \text{H}_2\text{O} < \text{C}_6\text{H}_5\text{OH} < \text{H}_2\text{CO}_3$. Phenol is more acidic than water but weaker than carbonic acid.

    Hint: Ethanol weakest; carbonic acid strongest here.

21. 21.Which reagent distinguishes a carboxylic acid from phenol, and how?

    $\text{NaHCO}_3$: carboxylic acids give brisk $\text{CO}_2$ effervescence; phenol does not react (too weak to displace $\text{CO}_2$ from bicarbonate).

    Hint: Only acids stronger than carbonic acid free CO₂.

22. 22.What reaction do alcohols and phenols give with active metals like sodium?

    They liberate $\text{H}_2$: $2\,\text{ROH} + 2\text{Na} \rightarrow 2\,\text{RONa} + \text{H}_2$. This shows the acidic O–H hydrogen. Sodium phenoxide / alkoxide is formed.

    Hint: Acidic H replaced by Na, gives H₂ gas.

23. 23.How does the reactivity of 1°, 2°, 3° alcohols towards HX compare, and why?

    Reactivity 3° > 2° > 1°. Reaction goes via carbocation ($S_N1$); the more stable the carbocation, the faster. tert-alcohols react even with conc. HCl at room temperature.

    Hint: Carbocation stability order.

24. 24.What is the Lucas reagent and what does the Lucas test distinguish?

    Lucas reagent = conc. HCl + anhydrous $\text{ZnCl}_2$. Distinguishes 1°/2°/3° alcohols by rate of turbidity (cloudy alkyl chloride).

    Hint: ZnCl₂ + conc. HCl; watch cloudiness.

25. 25.Give the Lucas test observations for 1°, 2° and 3° alcohols.

    3°: immediate turbidity. 2°: turbidity in ~5 min. 1°: no turbidity at room temperature (needs heating). Turbidity = insoluble R–Cl formed.

    Hint: 3° fast, 2° slow, 1° none cold.

26. 26.With which HX and conditions is the reaction of alcohols fastest? Give reactivity order of HX.

    HX reactivity: HI > HBr > HCl (bond strength / nucleophilicity). $-\text{OH}$ is a poor leaving group, so $\text{ZnCl}_2$ or acid protonates it to water first.

    Hint: HI most reactive; protonate OH → H₂O leaves.

27. 27.How are alkyl chlorides made from alcohols using $\text{SOCl}_2$? Why is it preferred?

    $\text{ROH} + \text{SOCl}_2 \rightarrow \text{RCl} + \text{SO}_2 + \text{HCl}$. Preferred because the by-products are gases that escape, leaving pure alkyl chloride.

    Hint: Thionyl chloride; both by-products are gases.

28. 28.What products form when alcohols react with $\text{PCl}_5$ and $\text{PCl}_3$?

    $\text{ROH} + \text{PCl}_5 \rightarrow \text{RCl} + \text{POCl}_3 + \text{HCl}$.
    $3\,\text{ROH} + \text{PCl}_3 \rightarrow 3\,\text{RCl} + \text{H}_3\text{PO}_3$.

    Hint: PCl₅ gives POCl₃; PCl₃ gives H₃PO₃.

29. 29.Describe acid-catalysed dehydration of ethanol and the conditions for ether vs alkene.

    $\text{C}_2\text{H}_5\text{OH} \xrightarrow[443\text{K}]{\text{conc. H}_2\text{SO}_4} \text{CH}_2=\text{CH}_2$ (elimination). At 413 K with excess alcohol, diethyl ether forms instead (substitution).

    Hint: High temp → alkene; lower temp → ether.

30. 30.Give the ease of dehydration order for 1°, 2°, 3° alcohols and the rule for the major alkene.

    Ease: 3° > 2° > 1° (carbocation stability). Major product follows Saytzeff's rule — the more substituted (stable) alkene predominates.

    Hint: 3° easiest; Saytzeff = most substituted alkene.

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