As shown in Fig. , in contrast to the concept of mass symmetry, N2 (A=3.1403, D 2 =0.9999) is more symmetric in comparison with O2 (A=3.2418, D 2 =0.9994) and F2 (A=3.5235, D 2 =0.9994). In addition, CO (A=3.2879, D 2 =0.9999) is also symmetric. For N2, n=6, i.e. 1C4+4C2+E, but A=3.1403. Therefore, an additional symmetry operation should be found. Conventionally, two π bonds are considered rigid. However, the σ bond's rotation must be included to ensure n/2>A. A σ bond rotation supplies two operations: a cross of p orbitals of two N atoms and a C2 of cross. Hence, n = 8 for N2. The twist of two π bonds is also acceptable, but we must endow a twist operation with RT. Comparatively, a σ bond rotation is a better choice universal to other molecules. As mentioned above (Fig. ), the C-C π bond in the ethylene and benzene ring does not exhibit symmetric superiority compared to ethane and cyclohexane. Hence, if the σ bond in ethylene and benzene could rotate freely as in ethane and cyclohexane, the similar A values could be rationally interpreted. Moreover, CO2 (A=4.2768, D 2 =1) should have more than nine symmetry operations. Only two σ bond rotations can supply so many symmetry operations. Those analyses are consistent with the oscillating structure of the π bond, namely that two bonded electrons may immigrate to one of the bonded atoms. CO is similar to N2 because a spare O p 2 orbital can form a π bond with a vacant C p 0 . Therefore, n=8, satisfying A=3.2879. Similarly, for CO2, immigrating one pair of spare O p 2 electrons between C and O increases the number of operations.