Question 1

Identify the reason for the highest boiling point of R-COOH as compared to alkanes, ethers, alcohols and aldehydes.

Accepted Answer

Carboxylic acids have higher boiling points than alkanes, ethers, alcohols, and aldehydes of comparable molecular mass. This is due to the presence of strong intermolecular hydrogen bonding in carboxylic acids. The highly polarized O-H bond, enhanced by the electron-withdrawing carbonyl group, allows carboxylic acid molecules to form strong hydrogen bonds with each other. Because of this extensive intermolecular hydrogen bonding, they often exist as dimers even in the vapor phase or in non-polar

Question 2

Identify the reagent used in following reaction. Benzoic acid [ ] Reagent Benzoyl chloride + phosphorous oxychloride + Hydrogen chloride

Accepted Answer

The reaction of benzoic acid with phosphorus pentachloride ( PCl _5) yields benzoyl chloride, phosphorus oxychloride ( POCl _3), and hydrogen chloride ( HCl ). C _6 H _5 COOH + PCl _5 C _6 H _5 COCl + POCl _3 + HCl Thus, the reagent used is PCl _5. Answer: PCl _5

Question 3

Which from the following is NOT a monocarboxylic acid?

Accepted Answer

Toluic acid is methylbenzoic acid, which contains one -COOH group. Acrylic acid is propenoic acid (CH_2=CH-COOH), which contains one -COOH group. Phthalic acid is benzene-1,2-dicarboxylic acid (C_6H_4(COOH)_2), which contains two -COOH groups. Thus, it is a dicarboxylic acid. Isobutyric acid is 2-methylpropanoic acid ((CH_3)_2CH-COOH), which contains one -COOH group. Therefore, phthalic acid is not a monocarboxylic acid. Answer: Phthalic acid

Question 4

Identify the product obtained when isopropyl magnesium chloride in dry ether reacts with dry ice forming a complex, hydrolysed further.

Accepted Answer

Isopropyl magnesium chloride is (CH_3)_2CHMgCl. Dry ice is solid CO_2. When a Grignard reagent reacts with dry ice, it undergoes nucleophilic addition to the carbonyl group of CO_2 to form a magnesium carboxylate complex. (CH_3)_2CHMgCl + O=C=O (CH_3)_2CH-COOMgCl Upon acid hydrolysis, the complex yields a carboxylic acid. (CH_3)_2CH-COOMgCl + H_2O (CH_3)_2CH-COOH + Mg(OH)Cl The product (CH_3)_2CH-COOH is 2-methylpropanoic acid. Answer: 2 - Methylpropanoic acid

Question 5

Identify final products in the following sequence of reactions RCOOH + R'OH H ^+ intermediate Ni , ^ H _2 Products

Accepted Answer

The first step is the Fischer esterification reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction produces an ester as the intermediate. RCOOH + R'OH H ^+ RCOOR' + H _2 O The intermediate formed is the ester RCOOR' . The second step involves the catalytic hydrogenation (hydrogenolysis) of the ester using hydrogen gas over a nickel catalyst at high temperature. This process cleaves the ester bond, reducing the acyl group ( RCO -) to a primary alcohol

Question 6

Identify the main product of following reaction

Accepted Answer

DIBAL-H (Diisobutylaluminium hydride) is a selective reducing agent. It reduces esters and nitriles to aldehydes. The reaction proceeds as follows: R - CO - O - R ' [ 2. H _3 O ^+] 1. DIBAL-H R - CHO + R '- OH Therefore, the main product is an aldehyde, RCHO . Answer: RCHO

Question 7

When will be the acidic character of carboxylic acid higher in following cases ?

Accepted Answer

Acidic strength of a carboxylic acid is directly proportional to its acid dissociation constant K_a. Higher the value of K_a, stronger is the acid. The relationship between pK_a and K_a is given by pK_a = - K_a. Thus, a higher value of K_a corresponds to a lower value of pK_a. Therefore, higher acidic character corresponds to a higher K_a value and a lower pK_a value. Answer: Higher K_a value and lower pK_a value

Question 8

When sodium bicarbonate is added to an organic compound, brisk effervescences is evolved. This indicate the presence of which functional group.

Accepted Answer

Sodium bicarbonate (NaHCO_3) is a weak base that reacts with compounds more acidic than carbonic acid (H_2CO_3). Carboxylic acids (- COOH ) react with sodium bicarbonate to produce sodium carboxylate, water, and carbon dioxide gas. The reaction is given by: R- COOH + NaHCO_3 R- COONa + H_2O + CO_2 The evolution of carbon dioxide (CO_2) gas is observed as brisk effervescence. This test is the standard qualitative test used to detect the presence of the carboxylic acid functional group in an organ

Question 9

What is the common name for the simplest carboxylic acid, HCOOH ?

Accepted Answer

The simplest carboxylic acid is HCOOH. Its IUPAC name is methanoic acid. Its common name is formic acid, derived from the Latin word 'formica' meaning ant, as it was first isolated from the destructive distillation of ants. Answer: Formic acid

Question 10

Which of the following is the strongest carboxylic acid?

Accepted Answer

The acidic strength of carboxylic acids depends on the stability of the conjugate base (carboxylate ion). Electron-withdrawing groups (EWG) stabilize the conjugate base through the -I effect, thereby increasing the acidic strength. Electron-donating groups (EDG) destabilize the conjugate base through the +I effect, decreasing the acidic strength. In the given options: ClCH _2 COOH has a - Cl group which exerts a strong -I effect. HCOOH has a hydrogen atom (reference for I effect). CH _3 COOH has

Question 11

Which is a weakest acid among the following ?

Accepted Answer

Acidic strength is directly proportional to the stability of the conjugate base. Electron-withdrawing groups (-I effect) stabilize the carboxylate ion and increase acidic strength, while electron-donating groups (+I effect) destabilize the carboxylate ion and decrease acidic strength. The +I effect of the isopropyl group ( CH _3)_2 CH - is greater than that of the methyl group CH _3-. Chlorine atoms exert a -I effect, which increases acidic strength. Thus, Cl _3 CCOOH and ClCH _2 COOH are strong

Question 12

Which of the following species is used in Friedel - Craft reaction?

Accepted Answer

Friedel-Crafts acylation is an electrophilic aromatic substitution reaction where an acyl group is introduced into an aromatic ring. The reagents typically used for this reaction are acyl halides (such as acid chlorides, R-CO-Cl) or acid anhydrides, in the presence of a Lewis acid catalyst like anhydrous AlCl_3. Among the given options, R-CO-Cl (acid chloride) is the correct species used in the Friedel-Crafts acylation reaction.

Carboxylic Acid Derivatives — Previous Year Questions & Solutions