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Organic Compounds containing C, H and O

Questions - Answers

2 Marks Questions

1. What is "Cannizzaro reaction"?
A: The reaction in which aldehydes (do not have alpha H) under go disproportionation on heating with strong alkali (Oxidised to salt of carboxylic acid & reduced to alcohol) is called Cannizzaro reaction.


 

2. What is meant by 'Decarboxylation'?
A: The phenomenon of lose of CO2 from the Sodium salt of Carboxylic acid when it is heated with sodalime (3 NaOH + 1 CaO) to form alkane.


 

3. What is 'Aldol condensation'?
A: The condensation of same aldehydes (having alpha hydrogen) in presence of dil.alkali to 

4. What is 'Cross Aldol condensation'?
A: The condensation of two different aldehydes (having alpha hydrogens) to form a mixture of 4 different enols, when heated with dilute alkali.


 

5. What is 'Hell - Volhard - Zelinsky (HVZ)' reaction?
A: The reaction in which halogenation takes place at alpha position of a carboxylic acid (having alpha hydrogen) when treated with a halogen (Cl2 or Br2) in presence of red Phosphorus.

6. What is 'Clemmensen reduction'?


 

7. What's Wolff - Kishner reduction'?

8. What is 'Rosenmund reduction'?
A: The reaction in which acid chloride (acylchloride) is reduced to aldehyde in presence of
Pd - BaSO4 Catalyst.


 

9. What is 'Gatterman - Koch reaction'?
A: The reaction in which benzene is converted into benzaldehyde when benzene is treated with CO, HC in presence of CuC or anhydrous AC3.

10. What is 'Etard reaction'?
A: The reaction in which methyl group is converted into aldehyde by the oxidation (with Cr2O2Cl2) of methyl group into Chromium complex followed by hydrolysis

11. What is 'Stephen reaction'?
A: The reaction in which -CN is reduced to imine by SnCl2 & HCl, which on hydrolysis gives aldehyde (- CHO).


 

12. What is 'Kolbe's reaction'?
A: The reaction in which Salicylic acid (2 - hydroxy benzoic acid) is formed when Phenol is treated with NaOH and CO2, H+.

13. What is 'Tollen's reagent'? Explain its reaction with aldehydes.
A: Tollen's reagent is ammonical silver nitrate. A bright silver mirror is formed when aldehyde is warmed with Tollen's reagent in alkaline medium.

14. What is "Fehling's reagent"? Explain its reaction with aldehydes?
A: The mixture containing equal amounts of Fehling solution A (aq. Copper sulphate) and Fehling solution B (alkaline sodium potassium tartarate) is called Fehling's reagents. When aliphatic aldehyde is heated with Fehling's solution, a reddish brown precipitate is formed.
e.g.: CH3CHO + 2 Cu+2 + 5 OH- > CH3OO- + Cu2O + 3 H2O

15. Give the major products that are formed by heating each of the following ethers with HI.


 

16. Write the equations for the following reactions.
i) Bromination of phenol to 2, 4, 6 - tribromophenol
ii) Benzyl alcohol to benzoic acid
A: i) Phenol gives white precipitate of 2, 4, 6 tribromophenol when it reacts with bromine water.

ii) Acidified KmnO4 Oxidise benzyl alcohol into benzoic acid.

17. While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which can be steam volatile. Give reason.

Due to weak intramolecular H - bonding, O - Nitrophenol has low boiling point, so it can be separated by steam distillation (as it is steam volatile).
Due to strong intermolecular H - bonding, P - Nitrophenol has high boiling point, so it can not be separated by steam distillation.

18. Alcohols boil at highest temperature than hydrocarbons and ethers of comparble molecular masses. Explain.
A: Due to intermolecular hydrogen bonding in alcohols they boil at highest temperature than hydro - carbons & ethers. Molecular masses of C2H5OH is 46, CH3OCH3 is 46, C3H8 is 44 but C2H5OH boiling point is high. But hydrocarbons, ethers does not form hydrogen bonds.

19. Ortho nitrophenol is more acidic than methoxy phenol. Explain. Why?
A: -NO2 is electron with drawing group and forms stable phenoxide ion by losing H+. So ortho nitrophenol is more acidic. -OCH3 (methoxy) is electron releasing group, which prevents the formation of phenoxide ion, so methoxy phenol is less acidic.

 

20. What is Aspirin? How is it prepared? Give its use.
A: Acetyl salicylic acid is called Aspirin. Salicylic acid on acetylation with acetic anhydride gives Aspirin.

It is used as analgesic, antiinflamatory and antipyretic.

FOUR MARKS QUESTIONS

1. Explain the acidic nature of phenols and compare it with that of alcohols.
A: Proton (H+) donor is acid - OH is electron with drawing group and is attached to sp2 carbon of benzene ring. As electronegativity of sp2 carbon of phenol, electron density decreases on Oxygen. This will increase the polarity of O - H bond and results increase in ionisation of phenols than that of alcohols. In alkoxide ion (RO-) the negative charge is localised only on Oxygen, where as in Phenol, charge is delocalised. Due to resonance, stable phenoxide ion is formed by losing H+ ion (easily).

Phenoxide ion is more stable than that of alkoxide ion acidity of phenols is more than that of alcohols. When electron with drawing groups like -NO2 are attached to benzene in ortho para positions in phenol acidic nature will increases further. From PKa data we will understand that phenol is million times more acidic than that of Ethanol.

2. Explain the following with suitable examples and write the equations.
a) Reimer - Tiemann reaction
b) Williamson's ether synthesis
A: a) Reimer - Tiemann reaction: The reaction in which phenol is converted to salicylaldehyde when phenol is treated with chlroform and aq.NaOH (or) KOH.

b) Williamson's ether synthesis: The method in which symmetrical or unsymmetrical ethers are prepared by the reaction between alkyl halide and sodium alkoxide.

3. Explain the following terms. Give an example of the reaction in each case.
a) Acetal b) Cyanohydrin c) Oxime d) Semicarbazone
A: a) Acetal: Acetaldehyde on reaction with 1 mole of monohydric alcohol (e.g.: CH3OH) in presence of dry HC gives Hemiacetal (in Greek Hemi means half) & with 2 moles give acetal.


 

b) Cyanohydrin: Acetaldehyde reacts with HCN to given acetaldehyde cyanohydrin. Acetone reacts with HCN to give acetone cyanohydrin.

c) Oxime: Acetaldehyde reacts with NH2OH to give Acetaldoxime. Acetone reacts with NH2OH to give acetone oxime.

d) Semicarbazone: Acetaldehyde and Acetone reacts with semicarbazide (H2N - NHCONH2) to give acetaldehyde semicabazone, acetone carbazone respectively.

Posted Date : 31-10-2020

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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