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प्रश्न
Explain why Lewis acid is not required in bromination of phenol?
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उत्तर
Usual halogenation is carried out in the presence of Lewis acid, \[\ce{FeBr3}\] which polarises the halogen molecule. In case of phenol, the polarisation of bromine occurs even in the absence of Lewis acid. This is because of highly activating effect of –OH group on the benzene ring. The reaction follows:
Note: In aqueous solution, phenol ionizes to give phenoxide ion. Due to the presence of the negative charge, the oxygen atom of the phenoxide ion donates electrons to the benzene ring to a large extent. As a result, the ring gets highly activated leading to the formation of trisubstituted product. On the other hand, in the non-polar solvents, the ionization of phenol does not occurs to a large extent. As a result, the -OH group donates electrons to the benzene ring only to a small extent. Consequently, the ring is activated slightly and, therefore, only monosubstitution occurs.
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संबंधित प्रश्न
Name the following compound according to IUPAC system.
\[\begin{array}{cc}
\phantom{........................}\ce{CH2OH}\\
\phantom{..................}|\\
\ce{CH3 - CH - CH2 - CH - CH - CH3}\\
\phantom{}|\phantom{.............}|\phantom{........}\\
\phantom{..}\ce{CH3}\phantom{..........}\ce{OH}\phantom{........}
\end{array}\]
Write IUPAC name of the following compound:
\[\begin{array}{cc}
\ce{H3C - CH - CH2 - CH - CH - CH2 - CH3}\\
\phantom{}|\phantom{.............}|\phantom{......}|\phantom{.........}\\
\phantom{}\ce{OH}\phantom{..........}\ce{OH}\phantom{...}\ce{C2H5}\phantom{......}
\end{array}\]
Write IUPAC name of the following compound:
C6H5 – O – C7H15(n−)
Give IUPAC name of the following ether:
\[\begin{array}{cc}
\ce{C2H5OCH2 - CH - CH3}\\
\phantom{.....}|\\
\phantom{.......}\ce{CH3}
\end{array}\]
Give IUPAC name of the following ether:
Ethylidene dichloride when boiled with aqueous solution of NaOH yields _______.
(A) formaldehyde
(B) acetaldehyde
(C) acetone
(D) ethyl methyl ketone
How is phenol converted into the following?
Benzene
Write the structures of the products when Butan-2-ol reacts with CrO3
Resorcinol on distillation with zinc dust gives _________.
IUPAC name of m-cresol is ____________.
The heating of phenyl methyl ether with HI produces:
IUPAC name of the compound is:
\[\begin{array}{cc}
\ce{CH3-CH-OCH3}\\
|\phantom{....}\\
\ce{CH3}\phantom{..}
\end{array}\]
Give IUPAC name of the compound given below.
\[\begin{array}{cc}
\phantom{}\ce{CH3 - CH - CH2 - CH2 - CH - CH3}\phantom{.}\\
\phantom{.........}|\phantom{...................}|\phantom{...........}\\
\phantom{..}\ce{Cl}\phantom{.................}\ce{OH}\phantom{..}
\end{array}\]
Arrange the following compounds in decreasing order of acidity.
\[\ce{H2O, ROH, HC ≡ CH}\]
Match the structures of the compounds given in Column I with the name of the compounds given in Column II.
| Column I | Column II | |
| (i) |  |
(a) Hydroquinone |
| (ii) |  |
(b) Phenetole |
| (iii) |  |
(c) Catechol |
| (iv) |  |
(d) o-Cresol |
| (v) |  |
(e) guinone |
| (vi) |  |
(f) Resorcinol |
| (g) Anisole |
Match the starting materials given in Column I with the products formed by these (Column II) in the reaction with HI.
| Column I | Column II | ||
| (i) | CH3—O—CH3 | (a) |  |
| (ii) | \[\begin{array}{cc} \ce{CH3}\phantom{..................}\\ \backslash\phantom{.............}\\ \ce{CH-O-CH3}\\ /\phantom{..............}\\ \ce{CH3}\phantom{..................} \end{array}\] |
(b) | \[\begin{array}{cc} \ce{CH3}\phantom{....}\\ |\phantom{.......}\\ \ce{CH3-C-I + CH3OH}\\ |\phantom{.......}\\ \ce{CH3}\phantom{....} \end{array}\] |
| (iii) | \[\begin{array}{cc} \ce{CH3}\phantom{.}\\ |\phantom{....}\\ \ce{H3C-C-O-CH3}\\ |\phantom{....}\\ \ce{CH3}\phantom{..} \end{array}\] |
(c) |  |
| (iv) |  |
(d) | CH3—OH + CH3—I |
| (e) | \[\begin{array}{cc} \ce{CH3}\phantom{.....................}\\ \backslash\phantom{.................}\\ \ce{CH-OH + CH3I}\\ /\phantom{.................}\\ \ce{CH3}\phantom{.....................} \end{array}\] |
||
| (f) | \[\begin{array}{cc} \ce{CH3}\phantom{.....................}\\ \backslash\phantom{.................}\\ \ce{CH-I + CH3OH}\\ /\phantom{.................}\\ \ce{CH3}\phantom{.....................} \end{array}\] |
||
| (g) | \[\begin{array}{cc} \ce{CH3}\phantom{....}\\ |\phantom{.......}\\ \ce{CH3-C-OH + CH3I}\\ |\phantom{.......}\\ \ce{CH3}\phantom{....} \end{array}\] |
Write structural formulae for:
p-Nitrophenol
Write the IUPAC name of the following compound:
\[\begin{array}{cc}
\phantom{..............}\ce{CH3}\\
\phantom{............}|\\
\ce{CH3 - CH - CH - C - CH3}\\
|\phantom{.....}|\phantom{......}|\\
\phantom{...}\ce{CH3}\phantom{.}\ce{OH}\phantom{...}\ce{CH3}
\end{array}\]
Write IUPAC name of the following compound:
\[\begin{array}{cc}
\phantom{...............}\ce{CH3}\\
\phantom{............}|\\
\ce{CH3 - CH - CH - C - CH3}\\
|\phantom{......}|\phantom{......}|\\
\phantom{...}\ce{CH3}\phantom{...}\ce{OH}\phantom{...}\ce{CH3}
\end{array}\]
Write the IUPAC name of the following compound:
\[\begin{array}{cc}
\phantom{...............}\ce{CH3}\\
\phantom{.............}|\\
\ce{CH3 - CH - CH - C - CH3}\\
|\phantom{......}|\phantom{......}|\\
\phantom{...}\ce{CH3}\phantom{..}\ce{OH}\phantom{...}\ce{CH3}
\end{array}\]
