The dipole moments of eighteen benzene derivative molecules were calculated theoretically, and the frequency doubling properties of their crystals were predicted. These molecular crystals have been synthesized and their frequency doubling effects and molecular dipole moments have also been measured. The theoretically predicted frequency doubling properties were in fair agreement with the measured values. This provides us new evidence that there is a correlation between the frequency doubling effects and the molecular dipole moments which was put forward by the authors some time ago. Four benzene derivatives that may become promising frequecy doubling materials have been selected. Among them the intensities of second harmonic efficiency of 3-MNA and 3-NBA is 7 and 2 respectively, with that of ADP taken as unity.