Variable-Temperature
Study of Hydrogen-Bond Symmetry
in Cyclohexene-1,2-dicarboxylate Monoanion in Chloroform‑<i>d</i>
Charles L. Perrin
Kathryn D. Burke
10.1021/ja500174y.s002
https://acs.figshare.com/articles/journal_contribution/Variable_Temperature_Study_of_Hydrogen_Bond_Symmetry_in_Cyclohexene_1_2_dicarboxylate_Monoanion_in_Chloroform_i_d_i_/2313667
The
symmetry of the hydrogen bond in hydrogen cyclohexene-1,2-dicarboxylate
monoanion was determined in chloroform using the NMR method of isotopic
perturbation. As the temperature decreases, the <sup>18</sup>O-induced <sup>13</sup>C chemical-shift separations increase not only at carboxyl
carbons but also at ipso (alkene) carbons. The magnitude of the ipso
increase is consistent with an <sup>18</sup>O isotope effect on carboxylic
acid acidity. Therefore it is concluded that this monoanion is a mixture
of tautomers in rapid equilibrium, rather than a single symmetric
structure in which a chemical-shift separation arises from coupling
between a desymmetrizing vibration and anharmonic isotope-dependent
vibrations, which is expected to show the opposite temperature dependence.
2014-03-19 00:00:00
temperature dependence
symmetry
cyclohexene
perturbation
carboxyl carbons
Chloroform
anharmonic
desymmetrizing vibration
equilibrium
mixture
chloroform
Monoanion
separation
tautomer
temperature decreases
carboxylic acid acidity
Symmetry
18 O isotope effect
NMR method
alkene
monoanion
hydrogen bond
magnitude
Cyclohexene