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 \(HCN\))\((ii) CH_3CH_2CH(Br)COOH,CH_3CH(Br)CH_2COOH,\)\((CH_3)_2CHCOOH,CH_3CH_2CH_2COOH\)(acid strength)\((iii)Benzoic\space acid,4-Nitrobenzoic \space acid\),\(3,4-Dinitrobenzoic \space acid,4-Methoxybenzoic \space acid\)(acid strength).
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 \(HCN\))\((ii) CH_3CH_2CH(Br)COOH,CH_3CH(Br)CH_2COOH,\)\((CH_3)_2CHCOOH,CH_3CH_2CH_2COOH\)(acid strength)\((iii)Benzoic\space acid,4-Nitrobenzoic \space acid\),\(3,4-Dinitrobenzoic \space acid,4-Methoxybenzoic \space acid\)(acid strength).
Solution and Explanation
(i)When \(HCN\) reacts with a compound, the attacking species is a nucleophile,\(CN^{-}\). Therefore, as the negative charge on the compound increases, its reactivity with HCN decreases. In the given compounds, the\( +I \) effect increases as shown below. It can be observed that steric hindrance also increases in the same.
Hence, the given compounds can be arranged according to their increasing reactivities toward HCN as:\(Di-tert-butyl \space ketone<Methyl \space tert-butyl \space ketone<Acetone<Acetaldehyde\)
(ii)After losing a proton, carboxylic acids gain a negative charge as shown:
Now, any group that will help stabilize the negative charge will increase the stability of the carboxyl ion and as a result, will increase the strength of the acid. Thus, groups having.\( +I \) effect will decrease the strength of the acids and groups having \(- I\) effect will increase the strength of the acids.In the given compounds,\(-CH_3\) group has \(+I \) effect and \(Br-\) group has \(-I\) effect.Thus,acids containing. \(Br-\) are stronger.
Now, the \(+I\) effect of isopropyl group is more than that of \(n-propyl \) group.Hence,\((CH_3)_2CHCOOH\) is a weaker acid than \(CH_3CH_2CH_2COOH\).
Also,the \(-I\) effect grows weaker as distance increases.
Hence, \(CH_3CH(Br)CH_2COOH\) is a weaker acid than \(CH_3CH_2CH(Br)COOH\).Hence,the strengths of the given acids increase as:\((CH_3)_2CHCOOH<CH_3CH_2CH_2COOH<CH_3CH(Br)CH_2COOH<CH_3CH_2CH(Br)COOH\)
(iii) As we have seen in the previous case, electron-donating groups decrease the strengths of acids, while electron-withdrawing groups increase the strengths of acids. As methoxy group is an electron-donating group,\(4-methoxybenzoic \space acid\) is a weaker acid than benzoic acid. Nitro group is an electron-withdrawing group and will increase the strengths of acids. As \(3,4-dinitrobenzoic \space acid\) contains two nitro groups, it is a slightly stronger acid than\( 4-nitrobenzoic \space acid\).Hence,the strengths of the given acids increase as:
\(4-Methoxybenzoic\space acid<Benzoic\space acid<4-Nitrobenzoic \space acid< 3,4-Dinitrobenzoic\space acid.\)
Top CBSE CLASS XII Chemistry Questions
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Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
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Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
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Top CBSE CLASS XII Aldehydes, Ketones and Carboxylic Acids Questions
What is meant by the following terms? Give an example of the reaction in each case.
\((i)\)\(Cyanohydrin\)
\((ii)Acetal \)
\((iii)Semicarbazone \)
\((iv)Aldol \)
\((v)Hemiacetal \)
\((vi)Oxime \)
\((vii)Ketal \)
\((vii)Imine \)
\((ix)\)\(2,4-DNP-derivative \)
\((x)Schiff's base\)Name the following compounds according to IUPAC system of nomenclature:
\((i) CH_3CH(CH_3)CH_2CH_2CHO \)
\((ii) CH_3CH_2COCH(C_2H_5)CH_2CH_2Cl \)
\((iii) CH_3CH=CHCHO \)
\((iv) CH_3COCH_2COCH_3 \)
\((v) CH_3CH(CH_3)CH_2C(CH_3)_2COCH_3 \)
\((vi) (CH_3)_3CCH_2COOH \)
\((vii) OHCC_6H_4CHO-p\)Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.
\((i) CH_3CO(CH_2)_4CH_3 \)
\((ii) CH_3CH_2CHBrCH_2CH(CH_3)CHO \)
\((iii) CH_3(CH_2)_5CHO \)
\((iv) Ph-CH=CH-CHO\)
\((v)\)
\((vi) PhCOPh\)Draw structures of the following derivatives.
(i)The 2,4-dinitrophenylhydrazone of benzaldehyde
(ii)Cyclopropanone oxime
(iii)Acetaldehydedimethylacetal
(iv)The semicarbazone of cyclobutanone
(v)The ethylene ketal of hexan-3-one
(vi)The methyl hemiacetal of formaldehydePredict the products formed when cyclohexanecarbaldehyde reacts with following reagents.
(i)\(PhMgBr\) and then \(H3O + \)
(ii)Tollens' reagent
(iii) Semicarbazide and weak acid
(iv)Excess ethanol and acid
(v) Zinc amalgam and dilute hydrochloric acid
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Concepts Used:
Aldehydes, Ketones, and Carboxylic Acids
Aldehydes, Ketones, and Carboxylic Acids are carbonyl compounds that contain a carbon-oxygen double bond. These organic compounds are very important in the field of organic chemistry and also have many industrial applications.
Aldehydes:
Aldehydes are organic compounds that have the functional group -CHO.
Preparation of Aldehydes
Acid chlorides are reduced to aldehydes with hydrogen in the presence of palladium catalyst spread on barium sulfate.
Ketones:
Ketones are organic compounds that have the functional group C=O and the structure R-(C=O)-R’.
Preparation of Ketones
Acid chlorides on reaction with dialkyl cadmium produce ketones. Dialkyl cadmium themselves are prepared from Grignard reagents.
Carboxylic Acid:
Carboxylic acids are organic compounds that contain a (C=O)OH group attached to an R group (where R refers to the remaining part of the molecule).
Preparation of Carboxylic Acids
Primary alcohols are readily oxidized to carboxylic acids with common oxidizing agents such as potassium permanganate in neutral acidic or alkaline media or by potassium dichromate and chromium trioxide in acidic media.