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Question

Q.(A)

(a) How will you convert the following :
(i) Propanone to Propene
(ii) Benzoic acid to Benzaldehyde
(iii) Benzene to m-Nitroacetophenone
(b)
(i) Arrange the following compounds in increasing order of their reactivity towards HCN : Propanone (CH3)2C=O(CH_3)_2C{=}O, Di-tert-butyl ketone ((CH3)3C)2C=O((CH_3)_3C)_2C{=}O, Ethanal CH3CHOCH_3CHO
(ii) Identify the compounds, which would undergo Aldol condensation : Methanal, HCHO Benzaldehyde, C6H5CHOC_6H_5CHO Ethanal, CH3CHOCH_3CHO Cyclohexanone (C6H10OC_6H_{10}O, drawn)
(OR)
(B)
(a) Give chemical tests to distinguish between the following pairs of compounds :
(i) Acetophenone and Benzophenone
(ii) Propanal and Propanone
(iii) Pentan-2-one and Pentan-3-one
(b)
(i) Which of the following acids is stronger and why ? CH2FCOOHCH_2FCOOH, CH3COOHCH_3COOH
(ii) Arrange the following compounds in the increasing order of their boiling points : CH3OCH3CH_3OCH_3, CH3CH2CH3CH_3CH_2CH_3, CH3CH2OHCH_3CH_2OH, CH3CHOCH_3CHO
CBSECBSE Class XII Board 2026Subjective· 5mImportance★★★★★
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Part (a): NaBH4_4/dehydration (propanone->propene), SOCl2_2+Rosenmund (benzoic acid->benzaldehyde), F-C acylation+nitration (benzene->m-nitroacetophenone); HCN reactivity di-tert-butyl ketone < propanone < ethanal; aldol given by ethanal and cyclohexanone. Part (b): iodoform/Tollens' distinguish the three pairs; CH2FCOOH>CH3COOHCH_2FCOOH>CH_3COOH; boiling points C3H8<CH3OCH3<CH3CHO<C2H5OHC_3H_8<CH_3OCH_3<CH_3CHO<C_2H_5OH.

Part (a)

(a) Conversions

  • (i) Propanone -> propene. Reduce the ketone to propan-2-ol (NaBH4NaBH_4), then acid-dehydrate:

CH3COCH3→NaBH4CH3CH(OH)CH3→conc. H2SO4, ΔCH3CH=CH2CH_3COCH_3 \xrightarrow{NaBH_4} CH_3CH(OH)CH_3 \xrightarrow{\text{conc. }H_2SO_4,\ \Delta} CH_3CH{=}CH_2

  • (ii) Benzoic acid -> benzaldehyde. Direct reduction over-reduces to the alcohol, so make the acid chloride, then use the selective Rosenmund reduction (Pd poisoned with BaSO4BaSO_4):

C6H5COOH→SOCl2C6H5COCl→H2, Pd-BaSO4C6H5CHOC_6H_5COOH \xrightarrow{SOCl_2} C_6H_5COCl \xrightarrow{H_2,\ Pd\text{-}BaSO_4} C_6H_5CHO

  • (iii) Benzene -> m-nitroacetophenone. Acylate first because −COCH3-COCH_3 is a meta-director; then nitrate:

C6H6→CH3COCl, anhyd. AlCl3C6H5COCH3→conc. HNO3/H2SO4m-NO2C6H4COCH3C_6H_6 \xrightarrow{CH_3COCl,\ \text{anhyd. }AlCl_3} C_6H_5COCH_3 \xrightarrow{\text{conc. }HNO_3/H_2SO_4} m\text{-}NO_2C_6H_4COCH_3

(b)(i) Reactivity toward HCN. Nucleophilic addition is faster with less steric bulk and a more electrophilic carbonyl: di-tert-butyl ketone < propanone < ethanal. …

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