the spectroscopic data for ( 4 ) , ( 3) , ( 2 ) , and ( I ) , n = 3 (see Table I).
Whilst the approximate agreement of the C-H stretching frequencies and "C-H coupling constants is not surprising and is no argument for or against the existence of conjugative interaction of the cyclopropane rings in ( I ) , n=3, the almost identical UV spectra of ( I ) , ri=3, and ( 2 ) can be regarded as evidence that (1 ), IZ = 3, represents no exception in the series ( 4 ) , ( 3 ) , ( 21, ( I ) , n=3. This is shown still more clearly by comparison of the 'H-and "C-NMR data. As would be expected if only inductive effects were operative, the ' Hand 'C-resonance signals are shifted by almost constant amounts along the series(4),( 3),( 2),(l),n=3: r(CH,)., and 6("C)>, consecutively by about 0.5 and 9 ppm, respectively, downfield, and T ( C H ? ) ~ and S('"C), consecutively by about 0.05 and 0.6 ppm, respectively, upfield['"'. Only the "C-resonance signals of the quaternary carbon atoms that would be intimately concerned in delocalization of the C-1, C-2 and C-1, C-3 hybrid orbitals deviate slightly from the additivity observed elsewhere for the shifts; thus the difference [A&('"C),] found on passing from (3) to (2) is 2.5 ppm but increases to 3.9 ppm on passing to ( I 1, n = 3 ; yet this deviation is too small to suggest delocalization of the cyclopropane hybrid orbitals in ( I ) , n=3.
We therefore expect that the strain energy of ( I ), n = 3 , will not fall much below the value 135.1 kcal/mol calculated from the strain energies of cyclopropane (27.15 kcal/ mol["') and spiropentane (63.13 kcal/mol)l"'~'ll.