My PhD dissertation - Institut Fresnel

3 Alkaline Decomposition of Phosphonium Salts: A
Probe to Assess Relative Stabilities of Alkyl Anions
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Carbanion chemistry plays a central role in modern synthetic organic chemistry.
This relationship has grown up at an extremely rapid pace since the 1960's, due to the
commercial availability of a variety of alkyllithium species, and the development of
efficient organometallic procedures
[ ] 105 . In fact, carbanions are not only involved as
nucleophiles in various chemical processes, but also as bases since deprotonation is often
required to initiate a reaction. This latter property made accessible many structural types
of transient reactive species which are highly valuable as synthetic units since they
generally undergo efficient carbon-carbon bond formation with various electrophiles. To
fine-tune the reaction conditions and select the most suitable reagent for a given
transformation, it is not enough to know that carbanions are globally reactive entities.
What we need is kind of a yardstick that allows us to evaluate the relative chemical
potential of any individual carbanionic reagent.
Despite the interest there would obviously be in the knowledge of their relative
stabilities, little is known about the simple hydrocarbon carbanions. For that purpose, few
investigations have been conducted to collect informations about the "acidity" of simple
alkanes, either in gas phase [106 - 108] or in solution [109 - 112] .
3.1 Gas Phase Acidities of Alkanes
The study of the gas phase chemistry of ionic species is of considerable
importance since it allows an assessment of the intrinsic molecular properties in the
absence of complex interactions with solvent molecules. Thus, in many instances, gas
phase data allow one to discern whether correlations deduced from solution phase data can
legitimately be interpreted in terms of properties of isolated molecules or should be
attributed to solvation phenomena. Although the gas phase acidities of a large number of