11. In this case there are 16 C " C sigma bonds and 10 C " H bonds. 12. The inductive effect drops across every sigma bond involved limiting its effect to only a few bonds. 13. Anchimeric assistance of the sigma bond between carbons 1 and 6 was rationalized as the explanation for this kinetic effect. 14. For there to be a constructive sigma bond formed after the shift, the reaction would have to be suprafacial. 15. In these compounds the central bond consists only of pi bonding because of a sigma antibond accompanying the sigma bond itself. 16. Silicon can form sigma bonds to other silicon atoms ( and disilane is the parent of this class of compounds ). 17. In the second step, the nucleophilic reagent ( Nuc : ) attaches to the carbocation and forms a covalent sigma bond . 18. Each silicon of the double bond uses its three " sp 2 " hybrid orbitals to form sigma bonds to three atoms. 19. Another difference is that the barrelene reaction requires the intersystem-crossing ( ISC ) to provide paired electrons and a new sigma bond . 20. A pi bond is generally weaker than a sigma bond , so easier for an electrophile ( aka lewis acid ) to go after.
