Kinetic Studies on Hydrogen Bonding in Quinone Anion Radical and the Dianion of Tetramethyl-1,4-Benzoquinone

The kinetic of hydrogen bonding of tetramethyl-1,4-benzoquinone (duroquinone, DQ) anion radical and dianion with methanol and ethanol was investigated in DMSO. The hydrogen bonding equilibrium constant and the (hydrogen bonding) rate constants were evaluated through the use of linear scan- and cyclic- voltammetry. It was found that the monoanion radical hardly undergoes any hydrogen bonding with the above mentioned hydrogen bonding agents. The hydrogen bonding equilibrium constant, Keq, for the process DQ + e DQ²⁻ , DQ²⁻ + m [HB] DQ²⁻(HB)m , (where HB is a hydrogen bonding agent and [ ] means large excess concentration) was found to be in the range of 2.3 x 105 M-m to 2.2 x 106 M-m, whereas the rate constants km were found to be [O] 106 M-m s-1 for ethanol and [O] 107 M-m s-1 for methanol. The hydrogen bonding number m was found to be ~3 for both alcohols

MAHBOOB MOHAMMAD, SABA RAUF, ASMA RAUF AND LUBNA NAZ