Advertisements
Advertisements
Question
Explain why Lewis acid is not required in bromination of phenol?
Advertisements
Solution
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.
APPEARS IN
RELATED QUESTIONS
Name the following compound according to IUPAC system.
\[\begin{array}{cc}
\phantom{............}\ce{CH2OH}\\
\phantom{......}|\\
\ce{CH3 - CH2 - CH - CH - CH - CH3}\\
\phantom{......}|\phantom{............}|\phantom{.}\\
\phantom{........}\ce{CH2Cl}\phantom{......}\ce{CH3}\phantom{}
\end{array}\]
Write structures of the compounds whose IUPAC names are as follows:
3-Chloromethylpentan-1-ol.
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:
CH3CH2CH2OCH3
Give IUPAC name of the following ether:
Write the structures of the products when Butan-2-ol reacts with SOCl2
Write the IUPAC name of the following :
Write IUPAC names of the following
Isopropyl alcohol on oxidation forms:
Ethylene reacts with Baeyer’s reagent to give ______.
The product of acid catalysed hydration of 2-phenylpropene is:
Write the IUPAC name of the compound given below.
\[\begin{array}{cc}
\phantom{}\ce{CH3 - CH2 - C = C - OH}\\
\phantom{........}|\phantom{....}|\phantom{}\\
\phantom{..............}\ce{CH3 CH2OH}
\end{array}\]
What happens when benzene diazonium chloride is heated with water?
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 |
Assertion: Phenol forms 2, 4, 6 – tribromophenol on treatment with \[\ce{Br2}\] in carbon disulphide at 273 K.
Reason: Bromine polarises in carbon disulphide.
Assertion: Phenols give o- and p-nitrophenol on nitration with conc. \[\ce{HNO3}\] and \[\ce{H2SO4}\] mixture.
Reason: –OH group in phenol is o–, p– directing.
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 the IUPAC name.
\[\begin{array}{cc}
\phantom{................}\ce{CH3}\\
\phantom{.............}|\\
\ce{CH3 - CH - CH - C -CH3}\\
\phantom{.}|\phantom{......}|\phantom{......}|\\
\phantom{....}\ce{CH3\phantom{...}\ce{OH}\phantom{...}\ce{CH3}}\
\end{array}\]
