Learn Carboxylic Acid MCQ questions & answers in Organic Chemistry are available for students perparing for IIT-JEE, NEET, Engineering and Medical Enternace exam.
61.
Which of the following compounds would have the smallest value for $$p{K_a}?$$
A
$$CH{F_2}C{H_2}C{H_2}COOH$$
B
$$C{H_3}C{H_2}C{F_2}COOH$$
C
$$C{H_2}FCHFC{H_2}COOH$$
D
$$C{H_3}C{F_2}C{H_2}COOH$$
Answer :
$$C{H_3}C{H_2}C{F_2}COOH$$
$$-F$$ is a strong electron withdrawing group. Electron withdrawing group present nearer to the $$-COOH$$ group has more acidic strength, hence low $$p{K_a}$$ value.
62.
Propionic acid with $$B{r_2} - P$$ yields a dibromo product. Its structure would be
A
B
C
D
Answer :
Carbonylic acids reacts with $$C{l_2}$$ or $$B{r_2}$$ in presence of red $$P$$ to give exclusively $$\alpha $$ - chloro or $$\alpha $$ - bromo acids. This reaction is called Hell-Volhard-Zelinsky $$(HVZ)$$ reduction. This reaction is example of $$\alpha {\text{ - }}H$$ - substitution.
63.
Which of the following carboxylic acids is highly insoluble in water?
A
Propanoic acid
B
Butanoic acid
C
Pentanoic acid
D
Decanoic acid
Answer :
Decanoic acid
Higher carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon part. Thus, decanoic acid is highly insoluble in water.
64.
An enantiomerically pure acid is treated with a racemic mixture of an alcohol having one chiral carbon. The ester formed will be
A
Optically active mixture
B
Pure enantiomer
C
Meso compound
D
Racemic mixture
Answer :
Optically active mixture
The optically active acid will react with $$d$$ and $$l$$ forms of
alcohol present in the racemic mixture at different rates to form two diastereomers in unequal amounts leading to optical activity of the product.
65.
The correct acidity order of the following is
A
(III) > (IV) > (II) > (I)
B
(IV) > (III) > (I) > (II)
C
(III) > (II) > (I) > (IV)
D
(II) > (III) > (IV) > (I)
Answer :
(III) > (IV) > (II) > (I)
Carboxylic acid is stronger acid than phenol. The presence of electron withdrawing group $$\left( {e.g\,\,Cl} \right)$$ increases acidic strength, while presence of electron donating group $$\left( {e.g\,\,C{H_3}} \right)$$ decreases acidic strength.
66.
The correct order of increasing acidic strength is _______.
A
phenol < ethanol < chloroacetic acid < acetic acid
B
ethanol < phenol < chloroacetic acid < acetic acid
C
ethanol < phenol < acetic acid < chloroacetic acid
D
chloroacetic acid < acetic acid < phenol < ethanol
No explanation is given for this question. Let's discuss the answer together.
67.
Which one of the following compounds undergoes decarboxylation upon heating ?
A
B
C
D
Answer :
\[\beta -\] Keto acids are decarboxylated by following mechanism
68.
What is the final product $$(B)$$ of this sequence ? \[\xrightarrow[\text{hight}]{B{{r}_{2}}}A\xrightarrow[2.\,{{H}_{3}}{{O}^{+}},\,\text{heat}]{1.\,KCN}B\]
A
B
C
D
Answer :
\[\left( A \right)\,Ph-C{{H}_{2}}-Br\xrightarrow{KCN}\] \[Ph-C{{H}_{2}}-C\equiv N\xrightarrow{{{H}_{3}}{{O}^{+}}}\] \[Ph-C{{H}_{2}}-C{{O}_{2}}H\left( B \right)\]
69.
Hydrolsis of an ester gives a carboxylic acid which on Kolbe’s electrolysis yields ethane. The ester is
A
ethyl methanoate
B
methyl ethanoate
C
methyl methanoate
D
methyl propanoate
Answer :
methyl ethanoate
Ethane is obtained by the electrolysis of sodium or potassium salt of ethanoic acid \[\left( C{{H}_{3}}COOH \right),\] hence the ester must be ethanoate \[C{{H}_{3}}COOR.\]