What is meant by the following terms? Give an example of the reaction in each case.
(i) Cyanohydrin (ii) Acetal (iii) Semicarbazone
(iv) Aldol (v) Hemiacetal (vi) Oxime
(vii) Ketal (viii) Imine (ix) 2,4-DNP derivative
(x) Schiff's base.
(i) Cyanohydrin: gem-Hydroxynitriles, i.e., compounds possessing hydroxyl and cyano groups on the same carbon atom are called cyanohydrins. These are produced by addition of HCN to aldehydes or ketones in a weakly basic medium.
(ii) gem – Dialkoxy compounds in which the two alkoxy groups are present on the terminal carbon atom are called acetals. These are produced by the action of an aldehyde with two equivalents of a monohydric alcohol in presence of dry HCl gas.
These are easily hydrolysed by dilute mineral acids to regenerate the original aldehydes. Therefore, these are used for the protection of aldehyde group in organic synthesis.
(iii) Semicarbazones are derivatives of aldehydes and ketones and are produced by action of semicarbazide on them in acidic medium.
(iv) Aldols are P-hydroxy aldehydes or ketones and are produced by the condensation of two molecules of the same or one molecule each of two different aldehydes or ketones in presence of a dilute aqueous base. For example,
(v)gem – Alkoxyalcohols are called hemiacetals. These are produced by addition of one molecule of a monohydric alcohol to an aldehyde in presence of dry HCl gas.
(vi)Oximes are produced when aldehydes or ketones react with hydroxyl amine in weakly acidic medium.
(vii) Ketals are produced when a ketone is heated with dihydric alcohols like ethylene glycol in presence of dry HCl gas or /3-toluene sulphonic acid (PTS).
These are easily hydrolysed by dilute mineral acids to regenerate the original ketones. Therefore, ketals are used for protecting keto groups in organic synthesis.
(viii) Compounds containing -C = N – group are called imines. These are produced when aldehydes and ketones react with ammonia derivatives.
(ix)2, 4-Dinitrophenyl hydrazone (i.e., 2,4-DNP derivatives) are produced when aldehydes or ketones react with 2,4-dinitrophenyl hydrazine in weakly acidic medium.
(x) Aldehydes and ketones react with primary aliphatic or aromatic amines to form azomethines or SchifFs bases.
Why are carboxylic acids more acidic than alcohols or phenols although all of them have hydrogen atom attached to an oxygen atom (-O-H)?
Name the electrophile produced in the reaction of benzene with benzoyl chloride in the presence of anhydrous AlCl3. Name of the reaction also.
Alkenes (>C = C<) and carbonyl compounds (>C = O), both contain a rc-bond but alkenes show electrophilic addition reactions whereas carbonyl compounds show nucleophilic addition reactions. Explain.
Assertion (A): Aldehydes and ketones, both react with Tollen's reagent to form silver mirror.
Reason (R): Both, aldehydes and ketones contain a carbonyl group.
Write down functional isomers of a carbonyl compound with molecular formula C3H6O. Which isomer will react faster with HCN and why? Explain the mechanism of the reaction also. Will the reaction lead to the completion with the conversion of whole reactant into product at reaction conditions? If a strong acid is added to the reaction mixture what will be the effect on concentration of the product and why?
Arrange the following compounds in increasing order of their boiling points:
CH3CHO, CH3CH2OH ,CH3OCH3, CH3CH2CH3
Assertion (A): Aromatic aldehydes and formaldehyde undergo Cannizzaro's reaction.
Reason (R): Aromatic aldehydes are almost as reactive as formaldehyde.
Assertion (A): The a-hydrogen atom in carbonyl compounds is less acidic. Reason (R): The anion formed after the loss of a-hydrogen atom in carbonyl compounds is more acidic.
Which acid of each pair would you expect to be stronger?
(i)CH3CO2H or FCH2CO2H
(ii)FCH2CO2H or ClCH2CO2H
(iii)FCH2CH2CH2CO2H
or CH3CH(F)CH2CO2H
Arrange the following in decreasing order of their acidic strength. Give explanation for the arrangement.
C6H5COOH, FCH2COOH, NO2CH2COOH
Addition of water to alkynes occurs in acidic medium and in the presence of Hg2+ ions as a catalyst. Which one of the following product will be formed on addition of water to but-l-yne under these conditions?
Which of the following is the correct representation for intermediate of nucleophilic addition reaction to the given carbonyl compound (A):
Name the following compounds according to IUPAC system of nomenclature:
(i) CH3CH (CH3)—CH2 CH2—CHO (ii) CH3CH2COCH(C2H5)CH2CH2Cl (iii) CH3CH=CHCHO (iv) CH3COCH2COCH3
(v)CH3CH(CH3)CH2C(CH3)2COCH3
(vi)(CH3)3CCH2COOH.
(vii)OHCC6H4CHO-p
What products will be formed on reaction of propanal with 2-methylpropanal in the presence of NaOH? Write the name of the reaction also.
Draw structures of the following derivatives:
(i)The 2,4-dinitrophenylhydrazone of benzaldehyde
(ii)Cydopropanone oxime
(iii)Acetaldehydedimethylacetal
(iv)The semicarbazone ofcyclobutanone
(v)The ethylene ketal of hexan-3-one
(vi)The methyl hemiacetal of formaldehyde
Through which of the following reactions number of carbon atoms can be increased in the chain?
(a) Grignard reaction (b) Cannizzaro's reaction
(c) Aldol condensation (d) HVZ reaction
Benzaldehyde can be obtained from benzalchloride. Write reactions for obtaining benzalchloride and then benzaldehyde form it.
Give simple chemical tests to distinguish between the following pairs of compounds.
(i)PropanalandPropanone (ii)Acetophenone and Benzophenone
(iii)Phenol and Benzoic acid (iv)Benzoic acid and Ethyl benzoate
(v)Pentan-2-one and Pentan-3-one (vi)Benzaldehyde and Acetophenone.
(vii)EthanalandPropanal
Which of the following compounds is most reactive towards nucleophilic addition reactions?
Assertion (A): Compounds containing -CHO group are easily oxidized to corresponding carboxylic acids.
Reason (R): Carboxylic acids can be reduced to alcohols by treatment with LiAlH4.
Carboxylic acids contain carbonyl group but do not show the nucleophilic addition reaction like aldehydes or ketones. Why?
Oxidation of ketones involves carbon-carbon bond cleavage. Name the products formed on oxidation of 2, 5-dimethylhexan-3-one.
Show how each of the following compounds can be converted into benzoic acid.
(i)Ethylbenzene
(ii)Acetophenone
(iii)Bromobenzene
(iv)Phenylethene (styrene)
Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.(i)CH3CO(CH2)4CH3 (ii) CH3CH2CH BrCH2CH(CH3)CHO (iii) CH3(CH2)5CHO (iv) Ph—CH=CH—CHO
An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B} and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (Q on dehydration gives but-l-ene. Write equations for the reactions involved.
Draw the structures of the following compounds:
(i) 3-Methylbutanal
(ii) p-Nitropropiophenone
(iii)p-Methylbenzaldehyde
(iv)4-Methylpent-3-en-2-one
(v)4-Chloropentan-2-one
(vi)3-Bromo-4-phenylpentanoic acid
(vii) pp’-Dihydroxybenzophenone
(viii)Hex-2-en-4-ynoic acid
An aromatic compound 'A' (Molecular formula CgHgO) gives positive 2, 4-DNP test. It gives a yellow precipitate of compound 'B' on treatment with iodine and sodium hydroxide solution. Compound 'A' does not give Tollens or Fehling's test. On drastic oxidation with potassium permanganate it forms a carboxylic acid 'C' (Molecular formula C7H6O2), which is also formed along with the yellow compound in the above reaction. Identify A, B and C and write all reactions involved.
Write structural formulas and names of four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde acts as nucleophile and which as electrophile.
Benzophenone can be obtained by
(a) benzoyl chloride + benzene + AlCl3
(b) benzoyl chloride + diphenylcadmium
(c) benzoyl chloride + phenylmagnesium chloride
(d) benzene + carbon monoxide + ZnCl2
Give the structure of the following compounds:
(a) 4-Nitropropiophenone
(b) 2-Hydroxycyclopentane + carbaldehyde
(c) Phenyl acetaldehyde
Arrange the following in decreasing order of their acidic strength and give reason for your answer.
An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B} and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (Q on dehydration gives but-l-ene. Write equations for the reactions involved.
Row will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom.
(i) Methyl benzoate (ii) m-nitrobenzoic acid (iii) p-nitrobenzoic acid
(iv) Phenylaceticacid (v) p-nitrobenzaldehyde
Describe the following:
(i) Acetylation (ii) Cannizzaro reaction
(iii) Cross aldol condensation (iv) Decarboxylation
When liquid 'A' is treated with a freshly prepared ammoniacal silver nitrate solution, it gives bright silver mirror. The liquid forms a white crystalline solid on treatment with sodium hydrogen sulphite. Liquid 'B' also forms a white crystalline solid with sodium hydrogen sulphite but it does not give test with ammoniacal silver nitrate. Which of the two liquids is aldehyde? Write the chemical equations of these reactions also.
Arrange the following compounds in increasing order of their property as indicated:
(i) Acetaldehyde, Acetone, Di-tert butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN) (ii) CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH, (CH3)2CH COOH,CH3CH2CH2COOH (acid strength).
(iii) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic add, 4-Methoxybenzok acid (acid strength).
Which of the following conversions can be carried out by Clemmensen reduction?
(a) Benzaldehyde into benzyl alcohol
(b) Cyclohexanone into cyclohexane
(c) Benzoyl chloride into benzaldehyde
(d) Benzophenone into diphenylmethane
