Ab initio calculations on spiropentane stereomutations lead to a reinterpretation of the experimental results

A study performed ab initio calculations of the potential energy surfaces for the stereomutations of spiropentane and cis- and trans-dimethylspiropentanes. The analysis aimed to better elucidate why disrotation is apparently preferred to conrotation in the pyrolyses of both the 1,2-dimethyl- and 1,2,4-trimethylspiropentanes. It also investigated why double rotation of C-1 and C-2 in the trans-1,2,4-trimethylspiropentanes is slower than epimerization at C-4. Results are discussed.