"Density Functional Investigation of Structures and Harmonic Force
Fields of Methyl-Substituted p-Benzoquinones"M. Nonella
J. Phys. Chem. 100, 1996, 20148-20155.
Structures and harmonic force fields of the methyl substituted
p-benzoquinones 2-methyl-1,4-benzoquinone, 2,3-dimethyl-1,4-benzoquinone,
2,6-dimethyl-1,4-benzoquinone, and 2,3,5,6-tetramethyl-1,4-benzoquinone
(duroquinone DQ) have been calculated by using density functional methods.
The calculations can successfully predict experimentally detected
frequencies in the 1500 to 1700 cm-1} region of the spectrum in all four
molecules. Occasionally, the mode assignment predicted by the calculation
differs from previously postulated assignments. In particular in the case
of DQ the calculations can successfully predict (i) the downshift of the
most intensive carbonyl mode from 1666 cm-1 in p-benzoquinone to around
1640 cm-1 in DQ due to a reduction of the force constant of the carbonyl
bond and (ii) the appearence of two isotopic shifts of similar size upon
18O labeling of both carbonyl groups as it has been found experimentally
in vitro and in photosynthetic reaction centers.
BMO authors (in alphabetic order):