We synthesized new low polar derivatives of tetrahydropyran with nematic and smectic behaviour. Quantum chemical calculations show, that the most elongated conformers of the cyclohexane and tetrahydropyran derivatives have nearly identical molecular shape. The different liquid crystalline behaviour can be explained by different amounts of conformers deviating from the most elongated shape. The Delta epsilon and Delta n have been calculated and compared with the experimental data obtained by extrapolation from basic mixtures. The two-ring compounds dissolved in the basic mixture have low order parameters and excellent solubility. By linear extrapolation, the two-ring compounds possess negative viscosities, but positive by logarithmic extrapolation.