Theoretical study of spiropentane, spiropentene and spiropentadiene

HF, MP2, and DFT calculations with 6-31G∗∗ and 6-311++G∗∗ basis sets were carried out for spiropentane, spiropentene, and spiropentadiene. The results of the calculations show that the NMR determination of HCH bond angle in spiropentane is more accurate than the value measured by electron diffraction. They also indicate that the assignment of one of the signals in the experimental NMR spectrum of spiropentene is in error. The calculations confirm earlier conclusions drawn on the basis of low-level ab initio calculations concerning the operation of spiroconjugation in the investigated molecules. They also demonstrate that there is a need for further experimental studies of these molecules.