On the existence of uncharged molecules with a pyramidally coordinated carbon: the cases of pentacyclo[4.3.0.0(2,9).0(3,8).0(7,9)]non-4-ene and heptacyclo- [7.6.0.0(1,5).0(5,15).0(6,14).0(10,14).0(10,15)]pentadecane.