Reaction of 7-carbomethoxy-cycloheptatriene with benzyne resulted in the formation of only one benzhomobarrelene isomer, 5A. Theoretically, four addition products, 5A-D, can be formed from this reaction. Certain molecular mechanic calculations (MM2 force field) have been undertaken on these isomers. It has been shown that the isomers 5A and 5C have the lowest energies. The non-existence of 5C has been discussed in terms of a benzyne approach to a norcaradiene structure. Furthermore, MM2 calculations on two different conformers of 5A have revealed that the bisected conformer 5AE has the highest strain energy. However, AM1 semiempirical calculations of those conformers have shown that the conformer 5AE possesses a lower heat of formation than the isomer 5AA.