mesogenic core axis can be easily understood. When the linking group X is replaced
by the carbonate group, the bimodal character of the distribution curve is largely
lost, and accordingly the distinction between those calculated for n ¼ odd and even
becomes obscure. The RIS analysis indicates that the angular distribution is
affected by the tilting angle (ϕ) of the first bond of the spacer C 1 –C 2 with respect
to the mesogenic core axis (shown by the bold lines in Fig. 4). Whereas ϕ is
estimated to be 5.3
and 8
respectively for the ether (Fig. 4b) and ester group
(Fig. 4c), ϕ amounts to 21.3
with the carbonate linkage (Fig. 4a). The bond angle
associated with the carbonate group –O–C(O)–O– is responsible for the depression
of the odd-even effect.
Fig. 4 Definition of the disorientation angle θ and the bond angles of the linking groups (X) used
in the RIS analysis: (a) carbonate, (b) ether, and (c) ester. The tilting angles (ϕ) between the first
bond of the spacer and the mesogenic core axis (bold lines) are estimated to be 21.3
, 5.3
, and 8
,
respectively, for the carbonate, ether, and ester group
114
A. Abe