Substituent effects on the relative rates and free energies of ortho-lithiation reactions: families of fluorobenzenes as the substrates
Year: 2015
Type: article
Abstract: 2-, 3-and 4-substituted fluorobenzenes and 5-substituted 1,3-difluorobenzenes were metalated with sec-butyllithium (LIS) and with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) under irreversible conditions in order to determine the rates of reaction relative to the unsubstituted parent compounds (fluorobenzene and 1,3-difluorobenzene).In addition, the pairs of resulting aryllithiums were subjected to acid-base equilibration to furnish the thermodynamic stabilities (or: basicities) of these species again relative to the parent compounds.Not surprisingly, the effect diminishes with the distance of a given substituent to the lithiation center (ortho > meta > para) and it reaches its maximum at the ground state equilibration of the organometallic intermediate whereas it fades away at transition states, in particular reactant-like ones.Fluorine, the most powerful activator in the entire series if located at an ortho position, increases the rates of LIS-and LiTMP-promoted metalations by respectively 2 and 3 powers of ten, but by 7 to 8 powers of ten the aryllithium equilibrium stability.
Source: ARKIVOC
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W2075160102