Give plausible explanation for each of the following:
(i) Cyclohexanone forms cyanohydrin in good yield but 2,2, fctrimethylcyclohexanone does not (ii) There are two – NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.
(iii)During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed.
The yield of second reaction is very low because of the presence of three methyl groups at ex-positions with respect to the C = O, the nucleophilic attack by the CN– ion does not occur due to steric hinderance. Since there is no such steric hindrance in cyclohexanone, therefore, nucleophilic attack by the CN– ion occurs readily and hence cyclohexanone cyanohydrin is obtained in good yield.
Although semicarbazide has two – NH2 groups but one of them (i.e., which is directly attached to C = O) is involved in resonance as shown above. As a result, electron density on N of this -NH2 group decreases and hence it does not act as a nucleophile. In contrast, the other -NH2 group (i.e.. attached to NH) is not involved in resonance and hence lone pair of electrons present on N atom of this -NH2 group is available for nucleophilic attack on the C = O group of aldehydes and ketones.’
(iii) The formation of esters from a carboxylic acid and an alcohol in presence of an acid catalyst is a reversible reaction.
Thus to shift the equilibrium in the forward direction, the water or the ester formed should be removed as fast as it is formed.
Why are carboxylic acids more acidic than alcohols or phenols although all of them have hydrogen atom attached to an oxygen atom (-O-H)?
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.
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): 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.
Arrange the following compounds in increasing order of their boiling points:
CH3CHO, CH3CH2OH ,CH3OCH3, CH3CH2CH3
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
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?
Assertion (A): Aromatic aldehydes and formaldehyde undergo Cannizzaro's reaction.
Reason (R): Aromatic aldehydes are almost as reactive as formaldehyde.
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
Carboxylic acids contain carbonyl group but do not show the nucleophilic addition reaction like aldehydes or ketones. Why?
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
Benzaldehyde can be obtained from benzalchloride. Write reactions for obtaining benzalchloride and then benzaldehyde form it.
What products will be formed on reaction of propanal with 2-methylpropanal in the presence of NaOH? Write the name of the reaction also.
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
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.
Show how each of the following compounds can be converted into benzoic acid.
(i)Ethylbenzene
(ii)Acetophenone
(iii)Bromobenzene
(iv)Phenylethene (styrene)
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
Oxidation of ketones involves carbon-carbon bond cleavage. Name the products formed on oxidation of 2, 5-dimethylhexan-3-one.
Give plausible explanation for each of the following:
(i) Cyclohexanone forms cyanohydrin in good yield but 2,2, fctrimethylcyclohexanone does not (ii) There are two – NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.
(iii)During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed.
Which of the following compounds is most reactive towards nucleophilic addition reactions?
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
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).
Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents. .
(i) PhMgBr and then H3O+
(ii) Tollen reagent
(iii) Semicarbazide and weak acid
(iv)Excess ethanol and acid
(v)Zinc amalgam and dilute hydrochloric acid
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.
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 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.
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.
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.
Describe the following:
(i) Acetylation (ii) Cannizzaro reaction
(iii) Cross aldol condensation (iv) Decarboxylation
An organic compound contains 69-77% carbon, 11-63 % hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tottens' reagent but forms an addition compound with sodium hydrogensulphite and give positive iodoform test. On vigorous oxidation, it gives ethanoic and propanoic acid. Write the possible structure of the compound.
Can Gattermann-Koch reaction be considered similar to Friedel-Crafts acylation? Discuss.
In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct answer out of the following choices:
(a) Assertion and Reason both are correct and Reason is the correct explanation of Assertion.
(b) Assertion and Reason both are wrong.
(c) Assertion is correct but Reason is wrong.
(d) Assertion is wrong but Reason is correct.
(e) Assertion and Reason both are correct statements but Reason is not the correct explanation of Assertion.
Assertion (A): Formaldehyde is a planar molecule.
Reason (R): It contains sp2 hybridised carbon atom.
Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions
(i)Ehtanal, propanaL, propanone, butanone
(ii)Benzaldehyde,p-Tolualdehyde, p-Nitrobenzaldehyde, acetophenone.
