AMBIDENT REACTIVITY OF ARYLOXIDE IONS TOWARDS 1,3,5-TRINITROBENZENE, LOW-TEMPERATURE CHARACTERIZATION OF THE ELUSIVE OXYGEN-BONDED SIGMA-COMPLEXES BY H-1 AND C-13 NMR-SPECTROSCOPY

The ambident reactivity of phenoxide ion towards 1,3,5-trinitrobenzene (TNB) was re-examined by means of a novel reaction system (CD3CN-glyme-d10) which allows the investigation of species formed at low temperatures (- 40-degrees-C), contrasting with previous studies in dimethyl sulfoxide (DMSO) at ambient temperature. The new method coupled with 400 MHz NMR spectroscopy has allowed the definitive observation of both O- and C-bonded phenoxide sigma-complex adducts for the first time, confirming the formation of the former through kinetic control and of the latter through thermodynamic control. The corresponding O-bonded sigma-adduct in the TNB-mesitoxide system (where C-bonded sigma-adduct formation is not possible but where there is competing nitro group displacement) has also been characterized by H-1 and C-13 NMR. Another O-bonded aryloxide adduct characterized is that from the reaction of TNB with 3,5-di-tert-butylphenoxide; in this system there is also competing NO2 displacement. Stereoelectronic factors in the O-bonded sigma-adducts and aryl ethers are discussed.