C-13 NMR spin-lattice relaxation times T-1 of quinoline (1) of some of
its methyl derivatives (quinaldine (3), lepidine (4), 6-methylquinoli
ne (5), 7-methylquinoline (6)) of isoquinoline (2), and of two quinoli
ne related compounds having two nitrogen atoms in one fused six-member
ed ring skeleton (quinazoline (7), quinoxaline (8)) have been measured
in pure liquid form as a function of temperature. The temperature ran
ge is not the same for all the compounds. It is at least 46 K for (7)
and it reaches 93 K for (4). In T-1 is plotted as a function 1 For (2)
, (6), (7) and (8) the data can be of the inverse of the absolute temp
erature T-1. For (2), (6), (7) and (8) the data can be accounted for b
y only one activation energy, for (1), (3), (4) and (5) by two activat
ion energies one above temperature T-t, one below. For all these compo
unds the high temperature relaxation corresponds to an energy barrier
which is less than 20.5 kJ mol(-1) and the low temperature process (wh
en a two energy barrier regime exists) corresponds to an energy barrie
r close to 30 kJ mol(-1). For quinoline and isoquinoline, the saturate
d specific heat C-s plotted as a function of T exhibits behaviour simi
lar to that of ln T-1 studied as a function of T-1. The results report
ed here suggest the existence of a dynamical transition in the liquid
state at a given temperature, a process somewhat similar to that propo
sed for some supercooled liquids.