A recently synthesized new molecule C-131 (C-60=C=C-70) is studied using the MNDO, AM1, PM3 and B3LYP methods. [6.6]-8 isomer is the most stable structure of C-131. To create C-60=C=C-70, the C-70 cage thermodynamically prefers to open bond (8) at the equatorial region. The strain analysis performed for the pristine C-70 (D-5h) and C-70 in C-131 revealed that the cycloaddition reaction occurring with the equatorial C-C bond (8) can lead to a larger strain release than occurring with the polar C-C bond (2) of C-70. The results provide new insights to understand the observations of C-60=C=C-70 as well as the previously reported C-70=C=C-70 and C70O (c) 2005 Elsevier B.V. All rights reserved.