Alcohols, Phenols, and Ethers - Class 12 Chemistry

A trihydric alcohol with three hydroxyl (-OH) groups attached to a propane molecule.

The IUPAC name for glycerol is propan-1,2,3-triol. It indicates a three-carbon chain (propane) with hydroxyl groups on carbons 1, 2, and 3.

The acidity of 2-chloroethanol is higher than ethanol due to the electron-withdrawing nature of the chlorine atom. This withdrawal weakens the O-H bond, making it easier to donate a proton.

Ethanol (ethyl alcohol) that has been made undrinkable by adding another chemical. This is done for safety and to prevent misuse.

The conversion of a secondary alcohol to a ketone involves oxidation. CrO3 or pyridinium chlorochromate are suitable reagents for this reaction.

Factors like hydrogen bonding between alcohol molecules and water, and the presence of a polar hydroxyl group, contribute to the solubility of alcohols in water.

The solubility of alcohols in water decreases as the length of the carbon chain increases. This is because the non-polar hydrocarbon chain becomes dominant, reducing the interaction with water molecules.

The IUPAC name for a compound depends on its structure. Identify the longest carbon chain, functional groups, and their positions to determine the correct name.

The C-O bond in phenol has a partial double bond character due to resonance, making it stronger than the single bond in methanol.

Phenol is a stronger acid than ethanol because the phenoxide ion formed after deprotonation is stabilized by resonance. Ethanol's ethoxide ion is destabilized by the electron-donating ethyl group.

Water has a higher acidity than ethanol because the electron-donating ethyl group in ethanol increases the electron density on the O-H bond, making it harder to release a proton.

The increasing order of acidity is ethanol < water < phenol. This is due to the resonance stabilization of the phenoxide ion, which makes phenol the strongest acid. Water is a stronger acid than ethanol due to the electron-donating effect of the ethyl group in ethanol.

The mechanism involves protonation of anisole, forming the methyl phenyl oxonium ion. The weaker O-CH3 bond breaks due to the partial double bond character of the O-C6H5 bond, leading to the formation of methyl iodide and phenol.

Cumene is the starting material used in the industrial preparation of phenol.

Bromination of phenol in an aqueous medium produces polyhalogenated derivatives with bromine replacing hydrogen atoms at ortho and para positions due to the phenoxide ion's strong activation of the benzene ring.

Lewis acid is not required for the bromination of phenol because the oxygen atom of phenol itself polarizes the Br2 molecule, forming Br+ ions. The +R effect of the OH group also activates phenol for electrophilic substitution.

Phenol is converted to aspirin through a series of steps involving the formation of sodium phenoxide, reaction with carbon dioxide, proton shift to form sodium salicylate, acidification to produce salicylic acid, and finally acetylation with acetic anhydride.

Enzymes like zymase are biocatalysts used in the industrial production of ethanol through fermentation of molasses. This involves breaking down sugars into smaller molecules without oxygen, yielding ethanol and CO2.

The -I effect of chlorine makes 2-chloroethanol more acidic than ethanol because it withdraws electron density from the O-H bond, making it easier to donate a proton.

Pyridinium chlorochromate (PCC) is a mild oxidizing agent that selectively converts primary alcohols to aldehydes without further oxidation to carboxylic acids.

Acidified potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7) act as strong oxidizing agents, converting primary alcohols to carboxylic acids.

o-Nitrophenol is more volatile than p-nitrophenol due to the presence of intramolecular hydrogen bonding, which prevents the association of molecules and allows for easier vaporization.

o-Nitrophenol is more acidic than o-cresol due to the electron-withdrawing effect of the nitro group, which stabilizes the phenoxide ion and makes it easier for the phenol to donate a proton.

When phenol reacts with bromine water, a white precipitate of 2,4,6-tribromophenol is formed due to electrophilic aromatic substitution.

o-Cresol < phenol < o-nitrophenol. The nitro group's -I and -R effects in o-nitrophenol enhance its acidity, while the methyl group's +I effect in o-cresol reduces its acidity.

Sodium reacts with alcohols to form alkoxides. The reactivity decreases from primary to tertiary alcohols because of the increasing +I effect of alkyl groups, which weakens the O-H bond and reduces alcohol acidity.

When benzene diazonium chloride is heated with water, it decomposes to form phenol, nitrogen gas, and hydrochloric acid. This reaction is a useful method for synthesizing phenol from aniline.

H2O > ROH > HC≡CH. Water is a stronger acid than alcohols because it can donate a proton more readily. Acetylene is the weakest acid because its conjugate base (acetylide ion) is stabilized by resonance.

Invertase and zymase are the enzymes involved in the fermentation of sucrose to ethanol. Invertase hydrolyzes sucrose into glucose and fructose, while zymase catalyzes the conversion of glucose and fructose to ethanol.

Propan-2-one (acetone) can be converted to tert-butyl alcohol by reacting with Grignard reagents, which add two alkyl groups to the ketone carbonyl group.

The –OH group in phenols is more strongly held than in alcohols due to the partial double bond character of the C-O bond in phenol, which results from resonance and charge delocalization in the benzene ring.

Phenols are less prone to nucleophilic substitution reactions because the electron-donating OH group increases the electron density of the benzene ring, making it less susceptible to nucleophile attack.

Alcohols can be prepared from alkenes by electrophilic hydration, which involves the addition of water to the alkene double bond in the presence of an acid catalyst.

CO2 is nonpolar because the two C=O bond dipoles cancel each other out due to their equal and opposite directions, resulting in a net dipole moment of zero. In contrast, ethers are polar because the oxygen atom is more electronegative than the carbon atoms, creating a dipole moment in the molecule.

The reactivity of alcohols with Lucas reagent (conc. HCl and ZnCl2) depends on the stability of the carbocation formed as an intermediate in the SN1 reaction. Tertiary alcohols react fastest because they form the most stable tertiary carbocation.

The presence of the -OH group in phenol increases electron density at ortho and para positions in the benzene ring due to the +R effect, making it more susceptible to electrophilic attack by NO2+ during nitration compared to benzene.

Phenoxide ion is more reactive than phenol towards electrophilic aromatic substitution due to its greater electron density, enabling it to react with carbon dioxide, a weak electrophile, in Kolbe's reaction.

The C-O bond in phenol is less polar than the C-O bond in methanol due to the electron-withdrawing effect of the benzene ring in phenol, resulting in a lower dipole moment.

Di-tert-butyl ether cannot be prepared by Williamson synthesis because the strong base nature of tert-butoxide ion leads to elimination instead of substitution with tert-butyl bromide, forming isobutylene.

The C-O-H bond angle in alcohols is slightly less than the tetrahedral angle due to the repulsion between the unshared electron pairs of oxygen. In ethers, the C-O-C bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky (-R) groups.

Alcohols with lower molar mass are more soluble in water due to their smaller hydrocarbon parts, allowing for stronger hydrogen bonding with water molecules compared to higher molar mass alcohols.

The electron-withdrawing nature of the nitro group in p-nitrophenol decreases the electron density in the O-H bond, making it more acidic compared to phenol. The phenoxide ion formed from p-nitrophenol is stabilized by the -NO2 group, further enhancing its acidity.

Ethers have weaker dipole-dipole forces compared to the strong hydrogen bonds in alcohols. Breaking the weaker forces in ethers requires less energy, leading to lower boiling points than their isomeric alcohols.

The carbon-oxygen bond in phenol is stronger than that in methanol due to the resonance between the unshared electron pairs on oxygen and the aromatic ring, resulting in partial double-bond character in the C-O bond.

The R-O-R bond in ethers is non-linear, resulting in a non-zero net dipole moment, making ethers polar in nature.

The stability of carbocations determines the reactivity of alcohols with Lucas reagent. Tertiary carbocations are the most stable, followed by secondary and then primary carbocations. Therefore, tertiary alcohols react the fastest, followed by secondary, and then primary alcohols.

In Williamson synthesis, the strong base nature of alkoxides can lead to elimination reactions, especially with tertiary alkyl halides, preventing the formation of di-tert-butyl ether.

Lower molar mass alcohols are more soluble in water due to their ability to form hydrogen bonds with water molecules. The smaller hydrocarbon parts in these alcohols allow for stronger hydrogen bond interactions.