The stabilities of Meisenheimer complexes. Part XI. The effects of ring-size of spiro-complex formation

Abstract

1 H N.m.r. measurements show that in dimethyl sulphoxide containing base 1-(3-hydroxypropoxy)- and 1-(4-hydroxybutoxy)-2,4-dinitronaphthalene cyclise to give spiro-Meisenheimer complexes containing respectively six-and seven-membered rings. Evidence is presented for a similar mode of action in water. Kinetic and equilibrium measurements are reported and compared with corresponding data for formation of the analogous complex containing a five-membered dioxolan ring. It is found that there is a dramatic decrease in complex stability on increasing the ring size from five to six or seven members. This reflects a large decrease in the rate of ring formation while the rates of ring opening are affected little by ring size.