In 1960, a group of chemists led by Prof. John D. Roberts at Caltech reported that when chlorobenzene containing a ¹⁴C isotopic label at carbon-1 is treated with the very strong base potassium amide, a substitution product, aniline, is formed in which the isotopic label is equally distributed between carbon-1 and carbon-2. This result was interpreted as evidence for a very interesting unstable intermediate called benzyne. Propose a mechanism for this substitution that accounts for the isotopic labeling result.

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* = carbon-14 Cl + K*:NH, chlorobenzene Figure P18.83 potassium amide liquid NH3 NH₂ aniline (about 50% of each) NH₂ + K+CI-