In particular, compounds of the general formula (I) wherein R is a straight alkyl group, R* is a 4-methylhexyl group, X is a fluorine atom which is substituted at 2-position of the p-phenylene group (i.e., 2-F) and n is 2, such as the compound Nos. 13, 16 and 22, are preferred in that they exhibit a ferroelectric liquid crystal phase over a wide range including room temperature.