Points to remember in Alcohol

$S_N 1 \text{ reaction:}$

PYQ-2023 Alcohol Q1, PYQ-2023 Alcohol Q7,

$ R - OH \xrightarrow{H^{\oplus}} R - \stackrel{\oplus}{O} H_{2} \xrightarrow{-H_{2} O} \stackrel{\oplus}{R} \xrightarrow{X^{\ominus}} R-X $ (R may rearrange)

Reactivity of $\mathrm{HX}$ : $\mathrm{HI}>\mathrm{HBr}>\mathrm{HCl}$

Reactivity of ROH : allyl, benzyl $>3^{\circ}>2^{\circ}>1^{\circ}$ (Carbocation) e.g.

$S_N 2 \text{ reaction:}$

$ROH+ PCl_{5} \longrightarrow RCl + POCl_{3}$

$ ROH + PCl_{3} \longrightarrow RCl + H_{3} PO_{3} $

$ ROH + SOCl_{2} \xrightarrow{\text { Pyridine }} RCl + SO_{2} + HCl $

Williamson’s synthesis :

It is the reaction in which sodium or potassium alkoxide is heated with an alkyl halide $\left(\mathrm{S}_{\mathrm{N}} 2\right)$.

This method is particularly useful for preparing mixed ethers.

Nucleophilic Aromatic Substitution of aryl halides $(S_N 2Ar):$

• An electron withdrawing group at ortho or para positions with respect to a good leaving groups are necessary conditions for $S_{N} 2$ Ar.

Intermediate ion is stabilized by resonance and are stable salts called Meisenheimer salts.

• A group that withdraws electrons tends to neutralize the negative charge of the ring and this dispersal of the charge stabilizes the carbanion.

$\hspace{15mm} Ar - S_{N} 2 \text { reaction. }$

$ (-\stackrel{+}{N}(CH_3)_3, -NO_2, -CN, -SO_3 H, -COOH, -CHO, -COR,-X) $

• A group that releases electrons tends to intensify the negative charge, destabilizes the carbanion, and thus slows down reaction.

$G(-NH_2 , -OH, -OR, -R)$ $\text{releases electrons : destabilizes carbanion, deactivates the} $ $Ar-{S}_{N} 2 \text{ reaction.}$

Element effect:

Reactivity order towards $\mathrm{S}_{\mathrm{N}} 2$ $\mathrm{Ar}$ with different halogens

$\mathrm{Ar}-\mathrm{F}>\mathrm{Ar}-\mathrm{Cl}>\mathrm{Ar}-\mathrm{Br}>\mathrm{Ar}-\mathrm{I}$

Physical Properties of Alcohol:

PYQ-2024-Genral_Organic_Chemistry-Q7, PYQ-2024-Alcohols-Q9

• Boiling Point: Alcohols generally have higher boiling points compared to other hydrocarbons with equal molecular masses. This is due to intermolecular hydrogen bonding between hydroxyl groups in alcohol molecules. As the number of carbon atoms in the aliphatic carbon chain increases, the boiling point also rises. Primary alcohols tend to have a higher boiling point.

• Solubility: Alcohol solubility in water is influenced by the hydroxyl group. Hydrogen bonds form between water and alcohol molecules, making alcohol soluble in water. However, the size of the alkyl group attached to the hydroxyl group affects solubility—the larger the alkyl group, the less soluble the alcohol.

• Acidity: Alcohols react with active metals (like sodium or potassium) to form corresponding alkoxides. This indicates their acidic nature. The polarity of the C-OH bond contributes to their acidity. Primary alcohols are generally more acidic than secondary and tertiary alcohols. Additionally, due to unshared electrons on the oxygen atom, alcohols can act as Bronsted bases.

Chemical Properties of Alcohols:

PYQ-2024-Alcohols-Q4,PYQ-2023 Alcohols Q4

• Oxidation: Alcohols undergo oxidation in the presence of an oxidizing agent. This produces aldehydes and ketones, which can further oxidize to form carboxylic acids.

• Combustion: When heated, ethanol undergoes combustion, producing carbon dioxide and water.

Formation of alcohol from cumene

PYQ-2023 Alcohols Q2

Dehydration of Alcohols

PYQ-2023 Alcohols Q3