Recent questions tagged ethers

Description : Ortho and paranitrophenols are more acidic than phanel. Draw the resonance structures of the corresponding phonoxide ion.

Last Answer : Ans:- Electronwithdrawal by nitro group makes the plenoxide ion more resonance stabilized and so the strength of phenel increases.

Description : Why phenol is acidic ?

Last Answer :  Ans: In phenol dissociation takes place as follows.   The conjugate base of phenol ie. Phenoxide ion is resonance stabilized. This is why the negative charge on oxygen atom is ... ion has less tendency to form undissociated phenol molecule and equilibrium lies towards right direction.  

Description : Why is it that secondary alcohols can only undergo a single oxidation step in contrast to primary alcohols?

Last Answer : 1. Once the oxidation has reached the ketone stage, (primary alcohols on oxidation yield aldehyde where as secondary alcohols on oxidation yield a ketone), it is impossible to put more oxygen atoms on the relevant carbon atom without rupturing the backbone of the molecule.

Description : Alcohols acts as weak bases. Explain.

Last Answer : The oxygen atom of the hydroxyl group has two lone pairs of electrons. Therefore alcohols accept a proton from strong mineral acid to form oxonium ions. Hence act as weak bases.

Description : Phenols do not undergo substitution of the — OH group like alcohols. Explain.

Last Answer : The C — O bond in phenols has some double bond character due to resonance and hence cannot be easily cleaved by a nucleophile. In contrast, the C — O bond in alcohols is a pure single bond and hence can be easily cleaved by a nucleo phile.

Description : Ethers are cleaved by acids not by based. Why ? 

Last Answer : The C - O - C bond in ethers like the C - OH bond in alcohols is quite strong. In order to weaken it, the oxygen atom must be protonated. A subsequent nucleophile attack by a strong ... protonation of O atom of ether and therefore only acids can bring about the cleavage of ethers and not bases.

Description : How an — OH group attached to carbon in the benzene ring activates benzene towards electrophilic substitution ?

Last Answer : The lone pair of electrons present on oxygen atom enter into resonance with the benzene ring. As a result, the electron density becomes higher at o- and p- position and due to higher electron density, the ring gets activated towards electrophilic substitution.

Description : While separating a mixture of ortho and para-nitro phenols by steam distillation, name the isomer which will be steam volatile. Give reasons.

Last Answer : In o-nitrophenol, there is intramolecular hydrogen bonding as follows : In p-nitrophenol, there is intramolecular hydrogen bonding as follows :   Due to intermolecular H ... -nitrophenol. Hence o-nitraphenol due to its lower b. p. is steam volatile while pnitrophenol is not.

Description : Di-tert butyl ether cannot be made by Williamson’s synthesis. Explain why ?

Last Answer : Ans. To prepare di tert-butyl ether by Williamson's synthesis, we need tert-butyl bromide and Sodium tertiary butoxide. Since tert-butyl bromide being 3°-alkyl halide prefers to ... rather than substitution, therefore the product obtained is isobutylene rather than ditertiary butyl ether.

Description : Alcohols are easily protonated than phenols. Justify.

Last Answer : Ans. In phenols lone pair of electrons on the oxygen atom are delocalised over the benzene ring due to resonance and hence are not easily available for protonation. In contrast in alcohols, ... oxygen atom are localized due to absence of resonance and hence are easily available for protonation. 

Description : Why are Grignard reagents soluble in ether but not in benzene ? 

Last Answer : Ans. Grignard reagents from co-ordination complexes with ether but not benzene since the former has lone pair of electrons but the later does not.

Description : Name the products obtained when anisole is treated with HI.

Last Answer : Ans. Phenol and methyl iodide. 

Description : Phenol has smaller dipole moment than methanol. (OR) Why are dipole moments of phenols smaller than dipole moments of alcohols ?

Last Answer : Due to electron-withdrawing effect of the benzene ring, the C — O bond in phenol is less polar but in case of methanol due to electron-donating effect of — CH3 group, C — O bond is more polar.

Description : What is usually added to ethyl alcohol to make it unfit for drinking purposes ?

Last Answer : Ans. Methanol and Pyridine. 

Description : What is the main product obtained when vapours of t-butyl alcohol are passed over copper at 300° ?

Last Answer : Ans. Isobutylene (2-Methyl propene)