Ambident reactivity of aryloxide ions towards 1,3,5‐trinitrobenzene, low‐temperature characterization of the elusive Oxygen‐bonded σ‐complexes by 1H and 13C 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°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 σ‐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 σ‐adduct in the TNB–mesitoxide system (whereC‐bonded σ‐adduct formation is not possible but where there is competing nitro group displacement) has also been characterized by 1H and 13C NBR. Another O‐bonded aryloxide adduct characterized is that from the reaction of TNB with3,5‐di‐tert‐butylphenoxide; in this system there is also competing NO2 displacement. Stereoelectronic factors in the O‐bonded σ‐adducts and aryl ethers are discussed.