Which of the following statements is/are correct regarding ethers?
A. Ethers have higher boiling points than alcohols with comparable molecular masses.
B. Williamson synthesis is a laboratory method for preparing symmetrical and unsymmetrical ethers.
C. The methoxy group in anisole (C6H5OCH3) is meta-directing and activates the aromatic ring toward electrophilic substitution reaction.
D. Anisole on reaction with HI gives a mixture of phenol and methyl iodide.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B and D only
In an ether (R–O–R′) the oxygen carries no hydrogen, so ether molecules cannot hydrogen bond with one another. In anisole, the lone pairs on the oxygen of –\( \ce{OCH3} \) are pushed into the benzene ring by resonance (+R effect). This raises the electron density at the ortho and para positions.
(A) Ethers have higher boiling points than alcohols with comparable molecular masses. — Incorrect. Alcohols are associated through hydrogen bonding, but ethers are not, so ethers boil much lower (diethyl ether 307.6 K against butan-1-ol 390 K).
(B) Williamson synthesis is a laboratory method for preparing symmetrical and unsymmetrical ethers. — Correct. An alkyl halide reacts with a sodium alkoxide by SN2.
\( \displaystyle \ce{R-X + R'-ONa -> R-O-R' + NaX} \)
(C) The methoxy group in anisole (\( \ce{C6H5OCH3} \)) is meta-directing and activates the aromatic ring toward electrophilic substitution reaction. — Incorrect. The –\( \ce{OCH3} \) group does activate the ring, but it is ortho and para directing, not meta directing.
(D) Anisole on reaction with HI gives a mixture of phenol and methyl iodide. — Correct. The O–C(aryl) bond has partial double bond character and is not broken. \( \ce{I^{-}} \) attacks the methyl carbon, so the O–CH3 bond breaks.
\( \displaystyle \ce{C6H5-O-CH3 + HI -> C6H5OH + CH3I} \)