Bridgehead ¹J(¹³C-H) values in 1,8-disubstituted 1a,2,7,7a- Tetrahydro-1,2,7-metheno-1H-cyclopropa[b]naphthalene compounds

Abstract

The value of the bridgehead ¹³C-H coupling constant tends to increase as the degree of "strain" increases in cyclic hydrocarbons. Thus, in the highly "strained" 1,3-dimethyltricyclo[1,1,1,0^4,5]pentane, the bridgehead J(¹³C-H) value is 212 Hz¹ and in the slightly less "strained" bicyclo[l,l,0]butane, the bridgehead ¹³C-H coupling is c. 200 Hz.² In both of these compounds the bridgehead proton is attached to two three-membered rings. When the bridgehead proton is common to two four-membered rings, such as in cubane and bicyclo[l,l,l]pentane,2 the coupling constant is c.160 Hz. In "unstrained" systems such as methane and cyclohexane the value is c.125 Hz.