THE KINETICS AND MECHANISM OF THE REACTION OF P-NITROCUMYL BROMIDE WITH NITRITE IONS IN DIMETHYL-SULFOXIDE - EVIDENCE FOR A NON-CHAIN REACTION GIVING A HIGH NITRO NITRITE RATIO IN THE PRODUCT/

The reaction of p-nitrocumyl bromide (RBr) with sodium nitrite in [H-2 (6)]dimethyl sulfoxide gives none of the conventional evidence for an S(RN)1 chain reaction but the initial values of the [RNO(2)]/[RONO] ra tio (2.5-5) are far higher than would be expected for the attack of a nitrite ion on the carbocation R(+) and increase with the concentratio n of nitrite ions, The high values of [RNO(2)]/[RONO] are considered t o derive from a mechanism in which a nitrite ion attacks a pi-complex derived from the carbocation R(+) and a second nitrite ion. This inter pretation is supported by a kinetic term that is second order with res pect to nitrite ions. An attempt to provide evidence for alternative r adical pair intermediates from N-15 CIDNP effects was unsuccessful.