Field induced changes in the ring/chain equilibrium of hydrogen bonded structures: 5-methyl-3-heptanol

Using non-linear dielectric techniques, we have measured the dynamics of 5-methyl-3-heptanol at a temperature at which the Kirkwood correlation factor g_K indicates the coexistence of ring- and chain-like hydrogen-bonded structures. Steady state permittivity spectra recorded in the presence of a high dc bias electric field (17 MV/m) reveal that both the amplitude and the time constant are increased by about 10% relative to the low field limit. This change is attributed to the field driven conversion from ring-like to the more polar chain-like structures, and a direct observation of its time dependence shows that the ring/chain structural transition occurs on a time scale that closely matches that of the dielectric Debye peak. This lends strong support to the picture that places fluctuations of the end-to-end vector of hydrogen bonded structures at the origin of the Debye process, equivalent to fluctuations of the net dipole moment or g_K. Recognizing that changes in the ring/chain equilibrium constant also impact the spectral separation between Debye and α-process may explain the difference in their temperature dependence whenever g_K is sensitive to temperature, i.e., when the structural motifs of hydrogen bonding change considerably.