When an ether containing a tertiary alkyl group is cleaved by $\text{HI}$:

• Protonation of ether gives oxonium ion: $(\text{CH}_3)_3\text{C}-\text{O}^+(\text{H})-\text{CH}_3$.
• Step 2 (slow, rate-determining): Cleavage of $\text{C}-\text{O}$ bond produces the highly stable tertiary carbocation $(\text{CH}_3)_3\text{C}^+$ and neutral $\text{CH}_3\text{OH}$ leaving group (Statement B).
• Because of stable carbocation formation, the pathway is $\text{S}_\text{N}1$ (Statement C).
• Fast attack of $\text{I}^-$ on the carbocation yields $(\text{CH}_3)_3\text{C}-\text{I}$.

Stepwise chemical transformations:

• $\text{CH}_3\text{Br (B)} + \text{Mg} \xrightarrow{\text{Dry Ether}} \text{CH}_3\text{MgBr (A)}$ (Grignard reagent formation)
• $\text{CH}_3\text{MgBr (A)} + \text{H}_2\text{O} \rightarrow \text{CH}_4\text{ (D)} + \text{Mg(OH)Br}$ (Hydrolysis to form alkane)
• $\text{CH}_4\text{ (D)} + \text{Cl}_2 \xrightarrow{\Delta / h\nu} \text{CH}_3\text{Cl (C)} + \text{HCl}$ (Free radical chlorination)

When phenol is treated with chloroform ($\text{CHCl}_3$) in the presence of aqueous sodium hydroxide, an aldehyde group ($-\text{CHO}$) is introduced at the ortho position of the benzene ring, yielding salicylaldehyde ($o$-hydroxybenzaldehyde). This reaction proceeds via the intermediate dichlorocarbene ($:\text{CCl}_2$) electrophile and is universally known as the Reimer-Tiemann reaction.