PENTAZOLE CHEMISTRY - THE MECHANISM OF THE REACTION OF ARYLDIAZONIUM CHLORIDES WITH AZIDE ION AT -80 DEGREES-C - CONCERTED VERSUS STEPWISE FORMATION OF ARYLPENTAZOLES, DETECTION OF A PENTAZENE INTERMEDIATE, A COMBINED H-1 AND N-15 NMR EXPERIMENTAL AND AB-INITIO THEORETICAL-STUDY

The reaction of p-chlorophenyldiazonium chloride with azide ion at -80 degrees C has been examined by H-1 and N-15 NMR spectra. The main pro duct, p-azidochlorobenzene? was present in the earliest spectra. Spect ra were obtained before the appearance of the second product, p-chloro phenylpentazole and an intermediate was observed. Correlated ab initio calculations at the MP2/6-31G level on 1H-pentazole and 1-phenylpent azole agree with the NMR spectra. An (E,Z)-arylpentazene 3 is the key intermediate leading to the 1-arylpentazole products. A (Z,E)-arylpent azene 2 leads directly to the aryl azide and is not convertible to the E-isomer. Three isomeric arylpentazenes, Z,E, E,E and E,Z are formed from initial azide ion attack at the diazonium beta-atom.