109. Identify the set of reagents that can effect bromination in benzene.
(a) Bromine/Hydrogen bromide
(b) Bromine/FeBr₃/H₂O
(c) Bromine/FeBr₃
(d) Bromine/FeBr₂
110. What is the reagent R in the reaction below?
COCl
|
\
R -> CHO
/
(a) LiAlH₄
(b) LiAlH[O(CH₃)₃]₃
(c) NaBH₄
(d) H₂/Ni
111. Carboxylic acids have higher melting points compared to alcohols with the same number of carbon atoms because:
(a) acids exhibit hydrogen bonding
(b) acids have higher molecular weight
(c) alcohols have polar character
(d) alcohols usually occur as dimers
112. Identify Q in the reaction represented by the equation below:
CONH₂
|
\
Q -> NH₂
/
(a) LiAlH₄
(b) KBr
(c) KMnO₄
(d) NaNH₂
113. Which of the following pairs of compounds will exhibit isomerism?
(a) C₄H₁₀ and C₂H₅O
(b) C₄H₁₀ and C₂H₆O
(c) C₄H₁₀ and C₂H₅O₂
(d) C₄H₁₀ and C₆H₁₂
114. An ester will not be formed when an alcohol is reacted with:
(a) a carboxylic acid
(b) an aldehyde
(c) an acid anhydride
(d) an acid chloride
115. Esters generally have lower boiling points than their corresponding carboxylic acids because:
(a) they are volatile
(b) they are associated
(c) they are not associated
(d) are non-volatile
116. Which of the following statement(s) is/are true of esters?
(a) they are colourless liquids
(b) they have a pleasant fruity odour
(c) they are used for flavouring
(d) all of the above
117. The reduction of esters to alcohols can be brought about by:
(a) LiAlH₄/C₂H₅OH
(b) LiAlH₄/(C₂H₅)₂O
(c) NaBH₄/(C₂H₅)₂O
(d) NaBH₄/C₂H₅OH
Answer (2)
The answers to the questions are as follows: 109 (c), 110 (b), 111 (a), 112 (a), 113 (none), 114 (b), 115 (c), 116 (d), 117 (a). Each selected reagent or explanation reflects the correct chemistry principles related to reactions and properties of organic compounds.
;
When brominating benzene, a catalyst is often required to facilitate the reaction. The set of reagents that can effect bromination in benzene is (c) Bromine/FeBr₃ . This is because benzene needs a strong electrophile to react, and the presence of the catalyst FeBr₃ aids in the generation of the bromonium ion which facilitates electrophilic substitution.
In the reaction where COCl becomes CHO, the reagent that can selectively reduce an acyl chloride to an aldehyde is (b) LiAlH[O(CH₃)₃]₃ . This reagent, known as lithium tri-tert-butoxyaluminum hydride, is used specifically to carry out this kind of selective reduction.
Carboxylic acids have higher melting points compared to alcohols with the same number of carbon atoms because (a) acids exhibit hydrogen bonding . While both can form hydrogen bonds, carboxylic acids form stronger dimeric hydrogen-bonded structures, leading to a higher melting point.
In the reaction where CONH₂ is converted to NH₂, the reagent used for this conversion is (a) LiAlH₄ . Lithium aluminum hydride is a powerful reducing agent capable of reducing amides to amines.
Isomerism occurs when compounds have the same molecular formula but differ in arrangement. The pair of compounds that will exhibit isomerism is (b) C₄H₁₀ and C₂H₆O . While not structural isomers, they illustrate different classes of isomerism: one is an alkane, the other an alcohol.
An ester will not be formed when an alcohol is reacted with (b) an aldehyde . Esters are usually formed by reacting an alcohol with a carboxylic acid or its derivatives, such as acid anhydrides or acid chlorides, but not with aldehydes.
Esters generally have lower boiling points than their corresponding carboxylic acids because (c) they are not associated . Carboxylic acids form strong hydrogen-bonded dimers, increasing their boiling points, whereas esters do not form such associations.
Esters are described by the statements (d) all of the above . They are typically colorless liquids, have a pleasant fruity odor, and are often used for flavoring due to their characteristic scents.
The reduction of esters to alcohols can be brought about by (b) LiAlH₄/(C₂H₅)₂O . Lithium aluminum hydride is a strong reducing agent commonly used to reduce esters to primary alcohols.
