Influence of Alkoxy
Groups on Rates of Acetal Hydrolysis
and Tosylate Solvolysis: Electrostatic Stabilization of Developing
Oxocarbenium Ion Intermediates and Neighboring-Group Participation
To Form Oxonium Ions
Angie Garcia
Douglas A. L. Otte
Walter A. Salamant
Jillian R. Sanzone
K. A. Woerpel
10.1021/acs.joc.5b00338.s001
https://acs.figshare.com/articles/journal_contribution/Influence_of_Alkoxy_Groups_on_Rates_of_Acetal_Hydrolysis_and_Tosylate_Solvolysis_Electrostatic_Stabilization_of_Developing_Oxocarbenium_Ion_Intermediates_and_Neighboring_Group_Participation_To_Form_Oxonium_Ions/2170654
The
hydrolysis of 4-alkoxy-substituted acetals was accelerated
by about 20-fold compared to that of sterically comparable substrates
that do not have an alkoxy group. Rate accelerations are largest when
the two functional groups are linked by a flexible cyclic tether.
When controlled for the inductive destabilization, an alkoxy group
can accelerate acetal hydrolysis by up to 200-fold. The difference
in rates of acetal hydrolysis between a substrate where the alkoxy
group was tethered to the acetal group by a five-membered ring compared
to one where it was tethered by an eight-membered ring was less than
100-fold, suggesting that fused-ring intermediates were not formed.
By comparison, the difference in rates of solvolysis of structurally
related tosylates were nearly 10<sup>6</sup>-fold between the five- and eight-membered ring series. This observation implicates neighboring-group
participation in the solvolysis of tosylates but not in the hydrolysis
of acetals. The acceleration of acetal hydrolysis by an alkoxy group
is better explained by electrostatic stabilization of intermediates
that accumulate positive charge at the acetal carbon atom.
2015-05-01 00:00:00
alkoxy group
Oxocarbenium Ion Intermediates
Form Oxonium IonsThe hydrolysis
acetal hydrolysis
acetal carbon atom