a liquid crystal substance having a large optical anisotropy value , a low viscosity and a superior compatibility with other liquid crystal compounds at low temperatures and also raising the degree of choice of liquid crystal materials and a liquid crystal composition containing the above substance are provided , which substance is a 4 -- 3 &# 39 ;, 4 &# 39 ;- difluorotolan expressed by the formula ## str1 ## wherein r represents an alkyl group of 1 to 10 carbon atoms .