In phenol OH –group directly attached to sp2 hybridised carbon of benzene ring act as a electron withdrawing group and is responsible for the acidic nature of phenol. Due to this .the lone pair of electrons of O-H are involved in resonance with C- atoms of benzene ring. As a result of resonance, the oxy gen atom acquires a partial positive charge. This weakens the O-H bond and thus facilitates the release of a proton.
1. Show the delocalisation of electron in phenol?
2. Which one is stronger acid, phenol or alcohol?
3. Give one reaction showing the acidic nature of phenol.
4. Arrange the following compound in the increasing order of acidic strength.
O-nitro phenol, o-cresol, phenol.
5. Write the name and give the structure of intermediate formed after the lossoh H+ ion from phenol.
Answers
Answer:
answer1. In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. ... In quantum chemistry, this refers to molecular orbital electrons that have extended over several adjacent atoms
ans 2. Phenols are much more acidic than alcohols because the negative charge in the phenoxide ion is not localized on the oxygen atom, as it is in an alkoxide ion, but is delocalized-it is shared by a number of carbon atoms in the benzene ring.
ans 3. The acidic nature of phenol can be represented by the following two reactions: (i) Phenol reacts with sodium to give sodium phenoxide, liberating H2. (ii) Phenol reacts with sodium hydroxide to give sodium phenoxide and water as by-products. The acidity of phenol is more than that of ethanol.
ans 4. Answer: Due to -1 and - R-effect of the group, o-nitrophenol is a stronger acid than phenol but do to +I-effect of the group, o-cresol is a weaker acid than phenol. Thus, acid . strength of these three phenols increases in the order : o-cresol < phenol < o-nitrophenol.
ans 5. Phenol is more acidic than ethanol because on losing H+ ions, phenol forms phenoxide ion and ethanol on losing H+ ion forms ethoxide ion. ... (ii) Propan-1-ol, 2,4,6-trinitrophenol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol.