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The rate-profile for the nitration of pyrazole over the range 90-99% sulphuric acid shows that the reaction involves the conjugate acid of pyrazole; this conclusion is supported by the Arrhenius parameters. Related arguments based on the rate profile and on a comparison with encounter rates show that the nitration of imidazole involves the conjugate acid. The reactivity

The halogenoboronation of phenylacetylene with boron trihalides (halogen = I, Br, or Cl) proceeds under kinetic control t o produce dihalogeno-(Z)-or (€)-2-halogeno-2-phenylvinyiboranes and ( < I 0%) dihalogeno-(Z)-or (€)-2-halogeno-1 -phenylvinylboranes. Subsequent reactions of these boranes with phenylacetylene produce halogenodivinyl-and trivinyl-boranes with the added acetylene substituting always as an (€)-2-halogeno-2phenylvinyl ligand. The differences in reactivity of boranes formed by addition of boron a t C-1 and -2 of the acetylene are discussed.