“Kinetically Enhanced Metalation”— How Substituents Direct ortho Lithiation

Not the complexation of the ground state but rather of the transition state explains the directing and activating effect of electronegative ortho substituents in the lithiation of aromatic compounds. Ab initio calculations show that the ground state of a C 6 H 5 FLiH complex for para metalation (complexation by the benzene ring) is energetically more favorable than that for ortho metalation (complexation by F), by −12.8 vs. −12.4 kcalmol −1 . In the transition state, however, the tables are turned; the respective activation barriers are +17.9 and + 6.5 kcalmol −1 . This is in accord with the experimental findings that only orhto ‐fluorolithiobenzene is formed.