Question

What is the correct method to synthesize 2-ethoxy-2-methylpropane, \( (CH_3)_3C-O-C_2H_5 \), by Williamson's synthesis?

• A. Using t-butyl alkoxide and ethyl chloride
• B. Using t-butyl chloride and ethoxide
• C. Using t-butanol and ethanol
• D. Using isopropyl chloride and isopropoxide

Hint:

Think about which alkyl halide can undergo a clean SN2 reaction without competing elimination.

Answer 1

The Correct Option is A

Step 1: Break the ether bond of \( (CH_3)_3C-O-C_2H_5 \) retrosynthetically into two possible ion pairs: (a) $(CH_3)_3C-O^-$ with $C_2H_5-Cl$, or (b) $C_2H_5-O^-$ with $(CH_3)_3C-Cl$.

Step 2: In every Williamson synthesis, the alkyl halide partner is the one that undergoes backside $S_N2$ attack, so its carbon must be as unhindered as possible. Compare the two halides: ethyl chloride has a primary carbon, while tert-butyl chloride has a tertiary carbon.

Step 3: A tertiary halide reacting with a small, strongly basic alkoxide such as ethoxide overwhelmingly undergoes E2 elimination instead of substitution, because the transition state for backside attack at a tertiary carbon is too crowded.

Step 4: Choosing pair (a), tert-butoxide (bulky base, fine as a nucleophile here) with ethyl chloride (primary, unhindered electrophile), removes this problem entirely, since substitution occurs at the primary carbon and elimination is not favored.

Step 5: This confirms that pair (a) is the workable combination for the synthesis.

\[ \boxed{(CH_3)_3C-O^- + C_2H_5Cl \rightarrow (CH_3)_3C-O-C_2H_5} \]