  Relative permittivities, $\varepsilon_{r}$, and refractive indices, $n_{D}$,
have been measured at (293.15-303.15) K, for the mixtures 1-pentanol +
2,5,8,11,14-pentaoxapentadecane (TEGDME) or TEGDME + octane. These data have
been used, together with density measurements available in the literature, to
calculate the correlation factors, $g_{K}$, according to the
Kirkwood-Fr\"ohlich equations. The curves of the deviations of from the ideal
behaviour, $\Delta\varepsilon_{r}$, of the 1-pentanol + TEGDME system are
shifted to high mole fractions of the alcohol, and show a rather large minimum.
The shape of the $\Delta\varepsilon_{r}$ curves of methanol + TEGDME or +
polyethylene glycol dimethyl ether 250 (PEG-250) mixtures is similar. This
reveals that polyethers can break the alcohol self-association even at high
alkanol concentrations. The higher $\Delta\varepsilon_{r}$ values of the
methanol solutions are ascribed to large self-association of this alcohol. The
$\Delta\varepsilon_{r}$ curves of the 1-pentanol + dibutyl ether (DBE) system
are nearly symmetrical, and the $\Delta\varepsilon_{r}$ values are higher than
those of the corresponding TEGDME mixture. This indicates that effects related
to the alcohol self-association are much more relevant in the DBE system. These
findings are supported by $g_{K}$ and molar polarization data. Values of molar
refraction of 1-pentanol systems reveal that dispersion forces become more
important in the sequence: octane < DBE < TEGDME. Such forces are also more
relevant in the 1-pentanol + TEGDME system than in the methanol + TEGDME
solution. The comparison of $\varepsilon_{r}$ and $g_{K}$ data for TEGDME or
DBE + octane mixtures shows than the polyether is a more structured liquid.
