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SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Max. Marks: 30 Max. Time: 40min Q1.write reaction to prepare phenol from chlorobenzene? Ans1.Dows-process C6H5Cl+NaOH 320atm,3600C C6H5OH(phenol) +NaCl [1] Q2.C6H5CH2Cl and C6H5CHClC6H5 which is more easily hydrolysed aq.KOH?Why?[1] Ans2. C6H5CH2Cl [alkyl halides are more easily hydrolysed being more reactive]. Q3.Distinguish between benzylchloride and chlorobenzene? C6H5CH2Cl + KOH (aq) boil C6H5CH2OH + KCl Benzyl chloride [1] Benzyl alcohol KCl + AgNO3 KNO3 + AgCl white ppt C6H5Cl (chlorobenzene) + KOH (aq) Δ no reaction (Ar-X less reactive than R-X) Q4. How is chloro benzene prepared from benzene and benzene diazonium chloride? Ans4. Raschig process or chlorination (Electrophylic substitution reactions) C6H6 + Cl2 FeCl3 C6H5Cl + HCl [2] Q5.Which is more reactive alkyl halide or aryl halide? Explain all the factors with the resonating structures? [3] Ans5. Alkyl halide (RX) are less reactive than aryl halide because of the following reasons: (i) Resonance Effect: Aryl halide are resonance stabilised than alkyl halides. Lone pair of electrons are delocalised over the benzene ring. As a result Carbon and halogen bond (C-X) in haloarenes acquires double bond character C=Cl while the other hand C-X bond is single in nature in alkyl halide (RX). Thus C-X bond in aryl halides are stronger than alkyl halides, hence haloalkanes (RX) are less reactive. Resonance structures can be written as: (ii) Hybridisation: In RX alkyl halides C attached to halogen is sp3 hybridised while in Ar-X C is sp2 hybridised. Therefore bond length in Ar-X is smaller than R-X. Therefore C-Cl bond is stronger in Ar-X than R-X. (iii) Dipole moment: C-X bond in aryl halide is less polar than alkyl halide (R-X) e.g. Chlorobenzene dipole moment is 1.69D while of CH3Cl is 1.86D. Due to above reasons halogen atom in aryl halide cannot be easily replaced by nucleophilic. Q6. Convert Benzene to diphenyl? C6H6+Cl2 FeCl3 C6H5Cl +HCl C6H5Cl + C6H5Cl 2Na Dry ether (fittig) C6H5-C6H5 [1] Diphenyl Q7. Convert chlorobenzene to phenol? [1] C6H5Cl +NaOH dil HCl 320 atm, 3600C Dow’s processC6H5OH + NaCl Q8. Benzene to chlorobenzene? C6H6+Cl2 anhyd FeCl3 C6H5Cl [1] +HCl Q9. Benzene to toluene? C6H6+ CH3Cl anhyd FeCl3 Friedel Craft reaction C6H5CH3 + HCl [1] Q10. Give mechanism of reaction when benzene is chlorinated. Electrophyllic substitution reaction [2] 1 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Q11.convert benzene to toluene C6H6+ CH3Cl anhyd FeCl3 C6H5CH3 +HCl or C6H6+Cl2 anhyd FeCl3 C6H5Cl +HCl C6H5Cl + CH3Cl 2Na Dry ether wurtz fittig C6H5CH3 [1] +2NaCl Q12. benzene to acetophenone C6H6+ CH3COCl anhyd. FeCl3 +HCl [1] friedel craft acylation C6H5COCH3 Q13. benzene to bromo benzene C6H6+Br2 anhyd. FeBr3 bromination C6H5Br [1] +HBr Q14.benzene to nitrobenzene C6H6+HNO3 H2SO4 nitration C6H5NO2+H2O [1] Q15.benzene to benzene sulphonic acid C6H6+ H2SO4 C6H5SO3H +H2O [1] Q16.convert aniline to phenyl isocyanide C6H5-NH2 + CHCl3 + 3KOH (alc) carbylamine C6H5NC + 3KCI + [1] 3H2O Q17.convert benzene to BHC or lindane or 666 C6H6+Cl2 hv, C6H6Cl6 [1]. Q18.convert chlorobenzene to diphenyl C6H6+Cl2 Anhyd. FeCl3 C6H5Cl +HCl C6H5Cl + C6H5Cl 2Na dry ether C6H5-C6H5 [1] +2NaCl Q19.convert aniline to benzene diazonium chloride. [1] C6H5NH2 + HONO (NaNO2+ HCl) diazotisation 273-278K C6H5N2Cl + 2H2O Q20.convert benzenediazonium chloride to bromo benzene Gattermann reaction: [1] Q21.Convert chlorobenzene to DDT? [1] Q22.Convert chloroform to tear gas? Cl3CH + OHNO2 Cl3CNO2 + H2O [1] Q23.Convert toluene to benzyl chloride (C6H5CH2Cl)? C6H5CH3 + Cl2 hv C6H5CH2Cl +HCl Q24.convert chlorobenzene to anisole [2] 0 C6H5Cl + NaOH Dow’s 320atm, 360 C C6H5ONa C6H5ONa + CH3Cl Williamson synthesis C6H5OCH3 [1] Chloroform nitric acid Q25. Ullmann reaction C6H5I +Cu +C6H5I --xxx— chloro picrin + +HCl NaCl [1] C6H5-C6H5 +CuI2 2 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Q1.Discuss briefly the following reaction (a) Balz-Shiemann reaction? C6H5N2Cl [1] + HONO, 273-278K diazotisation C6H5NH2 C6H5N2Cl Benzenediazonium chloride + HBF4 heat C6H5F Benzenediazonium chloride + N2 + BF3 Fluoro benzene (b) Wurtz reaction.Why it is not suitable for preparation of odd number alkanes? C2H5-Br + 2Na + Br-C2H5 dry ether wurtz C2H5-C2H5 + 2NaBr [2] Ethyl bromide Butane Because mixture of products are formed. This is not a suitable reaction to prepare higher unsymmetrical alkanes, as by-products are also formed during the reaction and thus their separation becomes difficult. (c) Friedel Craft acylation reaction for chlorobenzene? C6H5Cl + C6H5COCl Anhyd. AlCl3 [1] C6H4Cl COC6H5 o-p cholorobenzophenone (d) How does Iodobenzene reacts with copper powder in a sealed tube? What is the name of reaction? [1] C6H5I + Cu + IC6H5 Δ C6H5-C6H5 Iodo benzene Biphenyl + CuI2 Ullmann (e)Chlorobenzene to phenol? C6H5Cl + NaOH (3600C,320 atm P) Dow’s process (f) Finkelstein reaction? C2H5Cl + NaI acetone C6H5-OH+ NaCl [1] [1] C2H5-I + NaCl Ethyl Iodide Ethyl Chloride (g) Give 'Williamson Synthesis' reaction for sodium phenoxide with methylbromide. Write the names of this compound formed. [2] C6H5-ONa + Sodium phenoxide BrCH3 methyl bromide C6H5-O-CH3 Anisole + NaBr Q2. Give the name of the reaction, in which only haloarenes are treated with sodium, forming diaryls? [1] Fittig reaction Q3. Bromoalkanes can be easily prepared by refluxing the silver salts of a fatty acid. Name and explain the reaction. [1] CH3COOAg + Br2 350K, CCl4 REFLUX Borodine HDCH3Br + CO2 ↑ + AgBr Silver salt of acetic acid Bromo methane Silver bromide Borodine Hunsdiecker reaction Q4. How haloarenes are prepared from diazonium salts. Explain, by giving names of the reactions? [1] Ans Sandmeyer and Gattermann reaction C6H5N2Cl + CuBr / HBr sandmeyer Benzene diazonium chloride C6H5N2Cl C6H5Br + Bromobenzene + Cu / HBr Gattermann Benzenediazonium chloride N2 C6H5Br Bromobenzene + Cl- + N2 Q5. Convert benzene to chlorobenzene to phenol and chlorobenzene to phenol and phenol to benzene(4step)? [2] C6H6 + Cl2 FeCl3 chlorination,Electrophyllic Substitution Reaction C6H5Cl + HCl C6H5Cl + NaOH (3600C,320 atm Pressure)Dow’ s process C6H5-OH+ NaCl C6H5-OH+ Zn dust Dephenolation C6H6 + ZnO Q6.Convert butyl bromide to butyl-iodide? CH3CH2CH2CH2-Br + NaI acetone (Finkelstien) NaBr + CH3CH2CH2CH2-I Q7.What is Haloform reaction? [1] Q8.Give reactions of nitration of bromobenzene and bromination of nitrobenzene? [1] Q9. What is Hoffmann ammonolysis reaction? [1] CH3COCH3 + 3NaOI (I2+ NaOH) CI3COCH3 + 3NaOH Acetone Tri-Iodoacetone NaOH + CI3COCH3 CHI3 (yellow) Iodoform + CH3COONa [1] Nitration C6H5Br + HNO3/H2SO4 o-p nitrobromobenzne + H2O Bromination : C6H5NO2 + Br2 /FeBr3 m- bromonitrobenzene + HBr CH3CH2Br + H-NH2 C2H5OH CH3CH2NH2 +HBr CH3CH2Br + CH3CH2NH2 C2H5OH (CH3CH2)2NH +HBr CH3CH2Br + (CH3CH2)2NH (CH3CH2)3N +HBr 3 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Q10. Write Fermentation reactions from sucrose? [1] C12H22O11 sucrose Invertase enzyme + H2O C6H12O6 (Glucose) + C6H12O6 (Fructose) C6H12O6 (Glucose ) Zymase 2C2H5OH + 2CO2 Q11. Convert aniline to benzene diazonium chlroide? [1] (i) C6H5NH2+HONO(NaNO2+ HCl) diazotisation 273-278K C6H5N2Cl + 2H2O Q12. Give one chemical test to distinguish between carbon tetrachloride and chloroform?[1] Carbylamines test. CHCl3 + C2H5NH2 + 3KOH (alc) C2H5NC + 3KCl + 3H2O Chloroform 10 amine Ethyl Isocyanide (bad smell) Q13. Convert benzene to toluene? C6H5-Br + 2Na + Br–CH3 wurtz fittig Bromo benzene (Dry ether) Methyl bromide C6H5-CH3 + 2NaBr [1] (toluene) Q14. Convert benzene to chlorobenzene by Raschig process and then convert to diphenyl? [2] 2 C6H6+2HCl + O2(g) Raschig CuCl2 , 550K, heat 2C6H5Cl + 2H2O C6H5Cl + 2Na + ClC6H5 dry ether Fittig C6H5-C6H5 + 2NaCl Bromobenzene Biphenyl Q15. Write the reaction when 2-bromobutane is treated with alcoholic KOH? Ans15. Saytzeff rule [1] CH3-CH2-CHBr-CH3 + KOH (alc) Δ CH3-CH=CH-CH3 + CH3-CH2-CH=CH2 + KBr + H2O 2-Butene (80%) 1-Butene (20%) *** Max. Marks: 35 Q1.Which isomer of C4H9Cl will have the lowest boiling point? Ans1. 30 alkylhalide i.e. (CH3)3Cl because it is having lesser surface area. Reason: VanderWaal forces is directly proportional to surface area. Max. Time: 40min Q2. Write the reaction and formula of the main-product formed? (CH3)2CHCl Na, Dry ether ? + ? Ans2. (CH3)2CHCl Na, Dry ether ( Wurtz reaction) (CH3)2CH-CH(CH3)2 + [1] [1] 2NaCl Q3. How will you convert propene into propyne? [1] Ans3. CH3-CH=CH2 +Br2 CCl4 CH3-CH-CH2 + 2KOH (alc) CH3-CCH + 2KBr+ 2H2O ( Propene) | | ( Propyne ) Br Br Q4a. Markovnikov’s rule ? Ans4.When addition across an unsymmetrical alkene takes place, the -ve part of the addendum goes to that carbon atom of the double bond which holds the lesser number of hydrogen atoms. It takes place in the presence of mercuric acetate Hg(CH3COO)2. Or absence of peroxides Br CH3-CH=CH2 + HBr MARKONIKOV’S RULE CH3-CH-CH3 Propene (Unsymmetrical alkene) 2-Bromopropane Q4b. Anti Markonikov rule or peroxide effect or kharash effect. Ans4b. During addition of HBr (only) to unsymmetical alkenes in the presence of organic peroxide such as benzoyl peroxicle, (C6H5CO)2O2 –ve part of addendum goes to that C atom of double bond which has more no. of H atoms around double bond. It takes place contrary to the Markovnikov's rule. Also known as Peroxide effect or Kharasch effect. CH3-CH=CH2 + HBr ANTI-MARKONIKOV RULE (Presence of peroxides) CH3-CH2-CH2Br Q4c. Saytzeff rule in dehydrohalogention reaction? [3] ANS4C DEHYDROHALOGENATION : (1,2 ELIMINATION, β ELIMINATION) Saytzeff rule: It states that “In dehydrohalogenation reactions, the preferred product is that alkene which has lesser no. of H atom on doubly bonded carbon atoms or preferred product is that alkene which is more substituted. CH3-CH2-CH2-CH2Br + KOH(alc) Δ CH3-CH=CH-CH3 + CH3-CH2-CH=CH2 + KBr + H2O (more substituted) (Less substituted) 2-Butene (80%) 1-Butene (20%) 4 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Q5. Conversions: (a) Ethyl bromide into Propanoic acid? Ans5(a) C2H5Br+KCN(alc) (nculeophylic substitution ) C2H5CN C2H5CN+2H2O H+ acidic hydrolysis CH3COOH +NH3 [1] +KBr (b) How will you convert propene to 1-bromopropane? Ans5(b) CH3-CH=CH2 + HBr ANTI-MARKONIKOV’S RULE CH3-CH2-CH2Br [1] (c) Convert bromo methane to acetic acid? Ans5(c) C2H5Br+KOH(aq) hydrolysis CH3CH2OH +KBr CH3CH2OH + [O] KMnO4/H2SO4 CH3CHO + [O] KMnO4/H2SO4 [1] CH3CHO CH3COOH +H2O +H2O (d) Name the reagent used to convert 1-chroropropane to 1-nitropropane? Ans5(d) AgNO2 (e) Convert bromo ethane to butane? Ans5(e) C2H5Br +2Na +C2H5Br dry ether Wurtz reaction C2H5C2H5 Bromo ethane Butane [1] [1] + 2NaBr (f)1-Propanol to 2-bromopropane? Ans5f CH3CH2CH2-OH + Conc. H2SO4 443K CH3CH=CH2 CH3CH=CH2 + HBr MK RULE CH3CH(Br)CH2 2-bromopropane (g) CH3CH2Br + AgCN ? +? ANS5(g) CH3CH2Br + AgCN CH3CH2NC + AgBr (h) C2H5Br+ KOH (alc) ? +? ANS5(H) C2H5Br+ KOH (alc) DEHYDROHALOGENATION C2H4 + KBr + HOH [1] (i) Convert ethyl chloride to ethyl alcohol? ANS(I) C2H5Br + KOH (aq) HYDROLYSIS C2H5OH + KBr [1] (j) Convert silver acetate to methyl bromide? Ans (j) CH3COOAg +Br2 CCl4 REFLUX BORODINE HUNSDIECKER CH3Br + CO2 + AgBr [1] [1] [1] Q6. Alkyl halides though polar, are immiscible with water, why? [2] ANS6 Although alkyl halides are polar molecules, neither they form H bonds with water nor can they break H- bonds already existing between water molecules. As a result, the solubility of haloalkane in water is very low. Q7. Why is thionyl chloride method preferred for preparing alkyl chlorides from alcohol? [1] ANS7.Reaction: C2H5OH + SOCl2 C2H5Cl + SO2↑ + HCl ↑ Thionyl chloride (SOCl2) method is preferred to hydrogen halide or PCl5, PCl3 method as by products obtained are SO2 and HCl which are in gaseous state and which can escape leaving behind the chloroalkane in almost pure state. Q8. Treatment of alkyl halides with alc. AgNO2 give mainly nitroalkanes while that with aq. NaNO2 give mainly alkyl nitrites. Explain. [2] + ANS8. Because sodium nitrite ( NaNO2 ) is an ionic compounds and hence have –ve charge on one of the oxygen atoms. Nucleophile attack through this –ve charged Oxygen atom on the alkyl halide mainly gives the alkyl nitrite. R+ X+ +Na-NO2- RONO (alkyl nitrite) + NaX RX + Ag-NO2 C2H5OH/ H2O RNO2 + AgX Alkyl halide silver nitrite Nitro alkane In contrast silver nitrate (AgNO2) is a covalent compound and hence do not have a –ve charge on the O atom. Instead both the O atoms and the N atoms carry lone pair of electrons. Since N is less electronegative than oxygen, therefore lone pair of electrons on the nitrogen atom is more easily available for bond formation. In other hand, nucleophillic attack occurs through N and hence silver nitrite predominantly gives nitro compounds. Q9. Explain, why the treatment of alkyl halides with aqueous KOH leads to the formation of alcohols, but in the presence of alcoholic KOH. Alkenes are major products. [2] ANS9.SUSTITUTION OR ELIMINATION of alkyl halides depends upon nature of alkyl halide, strength and size of base or nucleophile and reaction conditions. RBr + KOH (aq) ROH + KBr RBr + KOH (alc) alkene + KBr + H2O it undergoes β dehydrohalogenation If the base is weak (KOH) or nucleophile is less concnentrated it results into substitution. Moreover in polar solvent, OH- ions are highly hydrated (solvated) hydration reduces basic character and therefore fails to abstract H from Carbon of alkyl halide to form alkene. If base is bulkier (stronger base) elimination predominates over substitution. 5 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] On the other hand alc KOH , contains alkoxide ion (RO-) which being stronger base than OH- preferentially eliminates a molecule of HCl from an alkyl halide to form alkene. 2-Bromobutane + (CH3)2COelimination CH2=CH-CH3 + HBr 2-Bromobutane + OHsubstitution CH2-CH(OH)-CH3 + BrQ10. What are ambident nucleophiles ? Explain with an example. [2] Ans10. Nucleophiles which have more than one site through which the reaction can occurs are called ambient nucleophiles. E.g. CN-,NO2- Q11.Which compound in each case reacts faster inSN2 reactions with -OH. (i) CH3Br or CH3I (ii) (CH3)3CCl or CH3Cl Ans11.CH3I (less bond enthalpy) (ii) CH3Cl (less stearic hinderance) Q12. Complete (CH3)3CBr+KOH ethanol/heat? Ans12. (CH3)3CBr+KOH Ethanol/heat (CH3)2C=CH2+KBr [1] +H2O Q13.Why Grignard reagent should be prepared in anhydrous condition? [1] Ans13. Grignard reagent are very reactive. They react with moisture present in the apparatus or the starting materials RX or Mg. RMgX +H2O RH +MgX(OH) Therefore they must be prepared in anhydrous conditions. Q14.Acetylene into propyne? Ans14. CHCH +Na liquid NH3 CHC-Na CHC-Na + CH3I NaI + CHC-CH3 [1] Q15.Propyne into 2-butyne? Ans15. CHC-CH3 + Na-CC-CH3 + [1] Q16.Ethane into ethylene glycol? Ans16. C2H6 + C2H5Cl + CH2=CH2 +[O] H2O Q17. Ethane into ethylene ? Ans17. C2H6 +Cl2 hv C2H5Cl + Na liquid NH3 CH3I Na-CC-CH3 CH3-CC-CH3 + NaI + NaI [1] Cl2 hv 573K C2H5Cl + HCl KOH (alc) CH2=CH2 +KCl +H2O alkaline KMnO4 CH2-CH2 (Baeyer ‘s reagent) | | OH OH [1] C2H5Cl + HCl KOH (alc) dehydrohalogenation CH2=CH2 + KCl + H2O Q18.Methyl bromide to ethylamine? C2H5Br + KCN(alc) C2H5CN +KBr C2H5CN + [H] Na/alcohol C2H5CH2NH2 Mendius-reduction Q19.Propane into propene? Ans C 3H 8 + Cl2 hv C3H7Cl + HCl C3H7Cl + KOH(alc) CH3-CH=CH2 + KCl [1] [1] +H2O Q20.Difference between SN1 and SN2 mechanism of nucleophillic substitution reactions? [2] SNI SNII First order reaction Second order reaction Rate =k [RX] Rate =k [RX] [Nu] One step reaction Two step reaction Reaction rate influence by electronic Reaction rate is determined by steric factors factors Racemic mixture: d+ l forms Inversion of configuration (Walden inversion) d to l form(vice-versa) Order: CH3X <10<20<30 < Allyl < benzyl Order : CH3X > 10 > 20 > 30 Nu can attack from back side as well as well The nucleophile(Nu-) can attack from from front side,however former predominates back side Rearrangement is possible. Rearrangement is not possible. 30 RX are common substrate i.e. presence of 10 RX are common substrates i.e. bulky group facilitates SN1 presence of simple and fewer R groups facilitates SN2 mechanism Reaction favoured by mild nucleophiles e.g. Favoured by strong nucleophile e.g. alcohol, water etc alkoxide ion(30alcohol) Favoured by low concentration of Favoured by high concentration of nucleophiles. nucleophiles Favoured by polar solvents(water). Favoured by non polar solvents or low polarity solvents(alcohol). Favoured by the presence of electrophilic Favoured by the absence of electrophilic catalysts catalyst. --xxx— 6 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Max. Marks: 40 Q1.What is meant by hydroboration reaction? Give example? Max. Time: 40min [1] Refer Reaction:34 of named reaction notes CH3-CH=CH2 + H-BH2 THB CH3-CH-CH2 CH3-CH=CH2 (CH3CH2CH2)2B-H Propene Borane H BH2 CH3-CH=CH2 (CH3CH2CH2)3B Tri-n-propylborane (CH3CH2CH2)3B + 3H2O2 OH ,H2O 3CH3CH2CH2OH+H3BO3 Diborane (B2H6) is an electron deficient molecule. Therefore, it acts as an electrophile and reacts with alkene to form trialkylboranes which upon subsequent oxidation with alkaline H2O2 to give alcohols. Thus, B2H6 2BH3 CH3-CH=CH2 + H-BH2 THB CH3-CH-CH2 CH3-CH=CH2 (CH3CH2CH2)2B-H Propene Borane H BH2 + CH3-CH=CH2 (CH3CH2CH2)3B tri-n-propylborane (CH3CH2CH2)3B + 3H2O2 OH- , H2O 3CH2CH2CH2OH + H3BO3 tri-n-propylborane Propan-1-ol Boric acid The addition of borane to the double bond takes place in such a manner that the boron atom gets attached to that carbon atom of the double bond which has greater number of hydrogen atoms. This two step process is called hydroboration oxidation and gives alcohols which seem to have been formed by Anti-Markovnikov’s addition of water to alkene. Q2. Complete the reaction: CH3CH2CH2OCH3 + HBr ? + CH3CH2CH2OCH3 + HBr CH3CH2CH2OH + CH3Br ? [1] Q3. Write Williamson’s synthesis reaction? [1] Reaction:13 of named reaction notes C2H5-Br + NaOC2H5 Williamson syn C2H5-O-C2H5 + NaBr Ethyl bromide Sodium Ethoxide Diethyl ether Q4. Write the reaction: (a) Propene to propan-1-ol ? Reaction:34 hydroboration oxidation CH3-CH=CH2 + H2O H-BH2 THB 3CH3CH2CH2OH [1] + H3BO3 Q5.Write IUPAC name for the following? CH3CH(OH)CH(CH3)CH2CH3 Ans5. 3-Methylpentan-2-ol [1] Q6. Explain: Why 10 alcohols are more acidic than 30 alcohol? [2] Due to +I effect electron density increases thus acidic character decreases, tendency to loose –OH increases with increase of +I effect. Release of H+ ions is easy in case of 10alcohol as compared to 30alcohol. Q7. Write reactions of acidic dehydration of ethanol to give ethene? CH3CH2OH Conc. H2SO4 443K CH2=CH2 + H2O [1] Q8.Which of two C6H5OH or C2H5OH is more acidic and Why? C6H5OH C6H5O- + H+ [2] resonance C2H5OH stabilised C2H5O- + not resonance H+ stabilised + Phenoxide ion formed after release of H ion is resonance stabilised as compared to alkoxide ion formed after release of H+ ion. Details: Why alcohols are weaker acids than water? (Marks 2) Ans. ACIDIC NATURE OF ALCOHOL: a. H2O > Primary alcohol > Secondary alcohol > Tertiary alcohol The acidic character of alcohols is due to the polar nature of O–H bond 7 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Alkyl group is an electron-releasing group (–CH3, –C2H5) or it has electron releasing inductive effect (+I effect). Due to +I effect of alkyl groups, the electron density on oxygen increases. This decreases the polarity of O-H bond. And hence the acid strength decreases. V imp Q13. why phenols are more acidic than alcohols? ACIDIC NATURE OF PHENOL: a. Phenol > H2O > Primary alcohol > Secondary alcohol > Tertiary alcohol The acidic character of alcohols is due to the polar nature of O–H bond Alkyl group is an electron-releasing group (–CH3, –C2H5) or it has electron releasing inductive effect (+I effect). Due to +I effect of alkyl groups, the electron density on oxygen increases. This decreases the polarity of O-H bond. And hence the acid strength decreases. b. Phenol is more acidic than alcohol because: In phenol, the hydroxyl group is directly attached to the sp2 hybridised carbon of benzene ring which acts as an electron withdrawing group. Whereas in alcohols, the hydroxyl group is attached to the alkyl group which have electron releasing inductive effect. In phenol, the hydroxyl group is directly attached to the sp2 hybridised carbon of benzene ring. Whereas in alcohols, the hydroxyl group is attached to the sp3 hybridised carbon of the alkyl group. The sp2 hybridised carbon has higher electronegativity than sp3 hybridised carbon. Thus, the polarity of O–H bond of phenols is higher than those of alcohols. Hence, the ionisation of phenols id higher than that of alcohols. The ionisation of an alcohol and a phenol takes place as follows: In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the charge is delocalised. The delocalisation of negative charge makes phenoxide ion more stable and favours the ionisation of phenol. Although there is also charge delocalisation in phenol, its resonance structures have charge separation due to which the phenol molecule is less stable than phenoxide ion. c. In substituted phenols, the presence of electron withdrawing groups such as nitro group enhances the acidic strength of phenol. On the other hand, electron releasing groups, such as alkyl groups, in general, decreases the acid strength. It is because 8 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] electron withdrawing groups lead to effective delocalisation of negative charge in phenoxide ion. (b) Phenols are less acidic than p-nitrophenol. Explain. (Marks 1,2) Ans. In –NO2 substituted phenols (p-nitrophenol), the presence of electron withdrawing groups –NO2 nitro group enhances the acidic strength of phenol. It is because electron withdrawing groups lead to effective delocalisation of negative charge in phenoxide ion. Q9. Write : (i) Lucas reagent (ii) Baeyer ‘s Reagent (iii) Jone’s reagent Anhyd. ZnCl2 +HCl Alkaline KMnO4 Jones reagent: chromic acid in aqueous acetone for controlled oxidation PCC: Pyridinium chloro chromate forcontrolled oxidation Refer: reaction:50 (v) Hybridisation of C bonded to –OH sp3 (iv) PCC Q10. Write conversions . (i) Ethane to ethyl chloride to butane to chlorobutane to butane to butanol? C2H6 + Cl2 hv,573 C2H5Cl +HCl Wurtz reaction C2H5Cl + C2H5Cl Na, Dry Ether C2H5-C2H5 +NaCl C4H10 + Cl2 hv,573 C4H9Cl + HCl C4H9Cl + KOH (aq) C4H9OH + KCl [5] [3] (ii) Ethane to ethyl chloride to butane to chlorobutane to butanol? Same as above (iii) Convert Propanal to 2-butanol? CH3CHO + CH3MgBr dry ether CH3C(OMgBr)HCH3 + CH3C(OMgBr)HCH3 + H2O / H acidic hydrolysis CH3CH(OH)CH2CH3 Q11.Give chemical test to distinguish between? (i) Methanol and ethanol Iodoform test:ethanol Yellowppt. CH3CH2OH + 3NaOI (I2+ NaOH) CHI3 (yellow + HCOONa Write reactions: ref reaction No.51(details) I2 + 2NaOH NaI + NaOI + H 2O CH3CH2-OH + NaOI CH3CHO + NaI + H2O 10 alcohol aldehyde 3NaOI + CH3CHO CI3.CHO + 3NaOH NaOH + CI3CHO CHl3 Iodoform (yellow) + HCOONa 2-butanol [3] CH3COOH no yellow ppt. (ii) 1-propanol & 2-propanol Iodoform test:2-propanol Yellow ppt. Write reactions: ref reactionNo.51 CH3COCH3 + 3NaOI CI3COCH3 + 3NaOH Acetone Tri-Iodoacetone NaOH + CI3COCH3 CHI3 (yellow) Iodoform + CH3COONa (iii) n-propyl chloride & iso-propylchloride iso-propylchloride +KOH (aq) 2-propanol +KCl Iodoform test:2-propanol yellow ppt. Write reactions: ref reactionNo.51 2-propanol + NaOI CH3COCH3 + NaI CH3COCH3 + 3NaOI CI3COCH3 + 3NaOH Acetone Tri-Iodoacetone NaOH + CI3COCH3 CHI3 (yellow) Iodoform + CH3COONa Q12.Complete the following: (i) C3H7ONa + C2H5Cl C3H7ONa + C2H5Cl Williamson synthesis C3H7OC2H5 [1] +NaCl Q13. Convert ethanol to propanoic acid? Ethnaol + SOCl2 pyridine C2H5Cl + SO2+ HCl C2H5Cl + KCN (alc) C2H5CN + KCl C2H5CN + 2H2O H+ C2H5COOH + NH3 [1] Q14. Convert Propan-1-ol to propan-2-ol? [1] 9 SACRED HEART SCHOOL Moga, Punjab Test XII-Chemistry [tests-organic-chemistry] Propan-1-ol + conc H2SO4 443K propene + water propene + H2O dil H2SO4 MK rule propan-2-ol Q15. Discuss the oxidation of 10, 20 and 30 alcohols by KMnO4 and by Cu-573K by taking suitable example? [6] Refer reaction : 50 , 52 CH3CH2OH + [O] KMnO4 CH3CHO + [O] CH3COOH Ethanoic acid Ethanol -H2O Ethanal OH O ║ CH-CH-CH3 + [O] KMnO4 CH3-C-CH3 propanone + [O] CH3COOH + H2O + CO2 or Propan-2-ol -H2O CH3COOH + HCOOH OH O ║ CH3-C-CH3 + [O] KMnO4 CH3-C-CH3+CO2+ 2H2O CH3COOH + H2O + CO2 CH3 2-Methyl propan-2-ol Propanone ( Lesser no. of Carbon atoms) Q16. A organic compound A (C2H6O) reacts with sodium to form a compound B with the evolution of H2 and gives a yellow compound C when treated with iodine and NaOH. When heated with conc. H2SO4 at 413K, it gives a compound D (C4H10O) which on treatment with conc. HI at 373K gives E. D is also obtained when B is heated with E. identify A, B, C, D and E. write equations for the reactants and products involved? [5] Ans16. A : 2CH3CH2OH + Na C2H5ONa (B) + H2 A: CH3CH2OH + NaOI (I2+ NaOH) CHI3 (C) + HCOONa A : 2 CH3CH2OH + conc H2SO4 413K C2H5OC2H5 (D) D C2H5OC2H5 + HI, 373K C2H5I (E) + C2H5OH C2H5ONa (B) + C2H5I (E) C2H5OC2H5 (D) + NaI Q17. Write CH3MgBr reactions with (a) Ethylene oxide (oxirane) (b) CO2 (c) Propanone (d) Ethyl acetate (e) Ethyl alcohol Products: propanol-1-ol (b) CH3COOH (c) 2-methyl propanol (e) C2H6 Refer reaction no. 33 --xxx-- [5] 10