NEW MATERIAL:The 3-fluorophenylcyclohexene derivative of formula I (R and R' are H, 1W20C alkyl or alkoxy).

EXAMPLE: 3-Fluoro-4-methyl-(4'-hexylcyclohexen-1'-yl)benzene.

USE: A component of a liquid crystal composition. It has small positive dielectric anisotropy and low viscosity, and useful to improve the low-temperature working characteristics of a liquid crystal composition.

PROCESS: The compound of formula I can be prepared by (1) reacting the 1- bromo-3-fluoro-4-substituted-benzene of formula II with a piece of Mg metal in tetrahydrofuran in N2 gas stream, (2) reacting the resultant 3-fluoro-4-substituted-benzene magnesium bromide of formula III with the 4-substituted-cyclohexanone of formula IV dissolved in tetrahydorfuran to obtain the compound of formula V, and (3) dehydrating the compound in N2 gas stream using KHSO4 as a catalyst.