Alcohols, Phenols And Ethers - Class 12 Medical Chemistry - Extra Questions

Since compound $$C_8 H_{10} O_2$$ corresponds positively to neutral $$FeCl_3$$. Hence it will be a phenol compound. 

Hydroxyl group attached to an aromatic ring is more acidic than the one in which hydroxyl group is attached to an alkyl group. Phenols are a million times more acidic than alcohols.

In alcohols,$$ -OH$$ group is attached to $$C$$ atom which is $$\displaystyle sp^3$$ hybridised. In phenols, $$-OH$$ group is attached to $$C$$ atom which is $$\displaystyle sp^2$$ hybridised.  $$\displaystyle sp^2$$ hybridised $$C$$ atom is more electronegative than $$\displaystyle sp^3$$ hybridised. Thus electron density on $$O$$ atom in phenol is lower than the electron density on $$O$$ atom in alcohol. Hence, the polarity of $$-OH$$ bond and ionization in phenol is more than that in alcohol.

Also when alcohols lose a proton, the resulting alkoxide ion has negative charge localised on $$O$$ atom. However when phenols lose a proton, the resulting phenoxide ion has negative charge of $$O$$ atom  delocalised  over ortho and para positions of aromatic ring. Hence, phenoxide ion is more stable than alkoxide ion.

The completed chemical reactions are as shown.
When ethanol is heated with sulphuric acid at 413 K, it is dehydrated to ethylene.
Treatment of tert butyl methyl ether with HI gives tert butyl iodide and methanol.
Sodium phenoxide reacts with alkyl halide to give arylalkyl ether.
Nitration of anisole with nitric acid/ sulphuric acid mixture gives a mixture of 2-nitroanisole and 4-nitro anisole.

Phenol is heated with phthalic anhydride in the presence of conc. $${H}_{2}{SO}_{4}$$ to give phenolphthalein.

a) i) The air oxidation of cumene (isopropyl benzene) leads to the production of both phenol and acetone, as shown in the following figure. The mechanisms for the formation and degradation of cumene hydroperoxide require closer looks, which are provided following the figure.
ii) $$C_6H_5OH+Zn\rightarrow C_6H_6+ZnO$$
b) The Williamson ether synthesis is a reaction, forming an ether from an organohalidecompound and a deprotonated alcohol (alkoxide).
$$R-O^{-}+R-X\rightarrow R-O-R+X^{-}$$

$$\displaystyle H-\underset {\displaystyle  \underset {\displaystyle \text {R}}{|} }{O}...H-\underset {\displaystyle  \underset {\displaystyle \text {R}}{|} }{O}...H-\underset {\displaystyle  \underset {\displaystyle \text {R}}{|} }{O}$$

Here addition of dilute $$HNO_3$$ leads to the addition of nitro group to the phenol. $$Sn/ HCL$$ acts as a reducing agent which is used to connect nitro-alkanes and nitro-arenes  to the corresponding primary amines.

To distinguish between phenol and benzoic acid consider the following reactions:

Yes, we can react salicyclic acid with $$pH-OH$$.

Reactions for the conservation of:

Phenol is more acidic than alcohol as it readily gives
$$H^+$$ to convert into more resonance stable phenoxide ion with a base while
it is very hard to remove $$H^+$$ from $$EtOH$$.

This is a case of extreme hydrogenation where the benzene ring loses its aromaticity to form a cyclohexane ring $$(C_6H_{12})$$
$$Toluene \xrightarrow[35\ atm,\ \Delta]{H_2,\ Pt/Al_2O_3}Methyl\  cyclohexane$$
Here, $$(T)$$ is Methyl cyclohexane $$(CH_3-C_6H_{11})$$

$$(a)$$ It involves a Friedel-Craft's acylation in the second step.
$$(b)$$ Here, Toluene is first converted to Benzene and then it is nitrated to get the desired product.

In water phenol exist as phenoxide ion,which is having more electron density thus nucleophilicity inncreases and hence show ,p-tribromo product,while in $$CS_2$$ solvent only +R effect of phenol is there so not so much nucleophilicity,show O or p bromo product.

The structures of $$A$$ and $$B$$ are given in the image.

Phenol on reacting with nitrating mixture produces p-nitrophenol and o-nitrophenol.
p-Nitrophenol can undergo intermolecular hydrogen bonding and thus has a higher boiling point. But o-nitrophenol undergoes intramolecular hydrogen bonding. As a result, it has a lower boiling point and is steam volatile.
Thus, they can be separated by steam distillation.

$$O- ,p-$$ nitrophenol are more acidic than phenol because of fact that $$NO_2$$ is best electron with drawing group.Electron with drawing groups increase acidic strength while electron donating groups decreases acidic strength.

Coupling occur at para position of phenol.

Phenoxide ion in phenol undergoes resonance stabilization. Therefore the conjugate base of phenol is more stable than that of ethyl alcohol.

Acidity $$\propto {\text{stability of conjugate base}}$$ 

Hence phenol is more acidic than ethyl alcohol.

Phenol is more acidic than alcohols due to stabilisation of phenoxide ion through resonance. Presence of electron withdrawing group increases the acidity of phenol by , stabilising phenoxide ion while presence of electron releasing group decreases the acidity of phenol by destabilising  phenoxide ion.

The substance which gives hydrogen ion when dissolved in water are known as acids.

Conjugate base of Phenol is stabilized by resonance therefore Phenol is acidic. However ethanol is basically neutral.

Ans-$$Acidic, neutral.$$

$$C_6H_5O-H \xrightarrow {-H^+} \underset{Phenoxide\ ion}{C_6H_5O^-}$$

Ans-$$Phenoxide\ ion.$$

Increasing order of acidity is ethanol < water < phenol. The phenoxide ion obtained after the removal of a proton is stabilized by resonance whereas the ethoxide loan obtained after the removal of a proton is destabilized by +I  Effect of  $$-C_2H_5$$ group. Therefore, phenol is a stronger acid than ethanol, On the other hand, ethanol is a weaker acid than water because electron releasing $$-C_2H_5$$ group in ethanol increases the electron density on oxygen and hence the polarity of $$O-H$$ bond in ethanol decreases which results in the decreasing acidic strength, Hence, acidic strength increases in the order given above.

Phenol Is a weaker acid than carbonic acid  ($$H_2CO_3$$) and hence does not liberate $$CO_2$$ from sodium bicarbonate.

$$Butane-2,3-diol$$

$$Propane-1,2,3-triol$$

Structure of the compound $$2-$$Methylbutan$$-2-$$ol is shown in the figure.

Two reactions that show the acidic nature of phenol are as follows:
$$(i)$$ The reaction of phenol with sodium to form sodium phenoxide with liberation of hydrogen gas.
$$\displaystyle C_6H_5OH + Na \rightarrow C_6H_5-ONa + \frac {1}{2}H_2 \uparrow$$
(ii) The reaction of phenol with sodium hydroxide to give sodium phenoxide and water.
$$\displaystyle C_6H_5-OH + NaOH \rightarrow C_6H_5-ONa + H_2O$$
Phenol is more acidic than ethanol.
Deprotonation of phenol gives phenoxide ion which is resonance stabilized.
There is no resonance stabilization for the deprotonation of ethoxide ion (obtained by deprotonation of ethanol).

Kolfe reaction in a reversible reaction at low temperature it form ortho isomer became ortho gram intra molecular hydrogen bond So at high temperature ortho can earily reverse reaction So ortho forms at low temperature 

As we can see from the mechanism that both $$OH^-$$ and $$Na^+$$ from $$NaOH$$ are essential for the formation of Salicylic acid. $$OH^-$$ abstracts the phenolic proton from $$Ph-OH$$ and $$Na^+$$ helps in coordinating $$CO_2$$ to the ortho-position via a six-membered transition state.

One of the  Important effects on the acidity of a molecule is if  the conjugate base anion can be stabilized by resonance. Phenol, for example , is stronger  acid than cyclohexanol  because the conjugate base of phenol is much more stable than the conjugate base of cyclohexanol. This added stability of the phenol conjugate base arises because this anion can delocalize the negative charge throughout the ring through resonance, effectively stabilizing it. The conjugate base of cyclohexanol has no resonance structures to stabilize the charge and so is less stable.

Phenol is a weaker acid than $$\mathrm{H_2CO_3}$$ and hence it does not react with $$\mathrm{NaHCO_{3}}$$.

The acidity of phenol is due to the Resonance Stabilisation of its anions.

Phenol gets slowly oxidised to a pink coloured compound p-benzoquinone when exposed to air.