Hybridization in highly strained small ring hydrocarbons—III : Unsaturated spiro-compounds

Abstract

Hybridization in spiro[2,4]hepta-4,6-diene (I), spiro[2,4]hepta-2,4,6-triene (II) and spiro[4,4]-nona-2,4,6,8-tetraene (III) is considered by applying the method of maximum overlap. The hybrids of the spiro carbon in I and II differ considerably from the sp 3-case. The presence of the carbon rings of different size leads to nonequivalent hybrids for the central carbon: sp 2·60 and sp 3·49 and sp 2·58 and sp 3·53 for I and II, respectively. The calculated exponents n of the sp n-hybrids for CH bonds are correlated with the τ values (chemical shifts) using a previously observed linear correlation τ = 5(n − 1). The reasons for some deviations from the above correlation are discussed.