Information about the structural flexibility of this compound can be experimentally obtained from the T1 relaxation times of the carbon resonances. The NT1 values (N = number of attached protons, T1 = longitudinal relaxation time) correlate directly with the molecular mobility.The experimental data provide us with information about the rotational motion of the backbone (Fig. 5).The NT1 value of the aromatic rings A and C in 4 increased compared with those in 2, indicating that the mobility was increased when the double bond was reduced. In this respect, the two consecutive methylene carbons at C-7 and C-8 of 4 have also large NT1 values. There was no difference between 2 and 4 about the NT1 values of the aromatic rings B and D. This supports the finding that reduction of the double bond at C-7 caused increase in the mobility, which agrees with the results of MC and MD simulations as described above.