Letter

Abstract

I am grateful to the Editors for affording me the opportunity of writing a final letter in this discussion. The fundamental idea underlying my earlier letter¹ was that the carbon atoms in cyclopropane and ethylene oxide were in a hybridization state close to that of the carbon atoms in ethylene. The evidence was then strong. Dr. J. W. Linnett has since pointed out that the CH stretching force-constant in these molecules is much closer to the ethylene than to the paraffinic CH₂ value. This developed a point already made, that the height of the strong Raman frequencies indicated the same conclusion. The Bastiansen–Hassel determination of the angle HCH in C₃H₈ as 118° ± 2 provides further strong evidence for my fundamental point. (The smaller angle in the 1,1 dichloro derivative (112° ± 4 ²) is expected since the angle ClCCl in the comparable 1,1 dichloro ethylene is reported as several degrees smaller than the angle HCH in ethylene.) Dr. H. A. Skinner's finding of accord between the Bastiansen–Hassel model and the measured moments of inertia reinforces the argument. Evidence from widely separated sources all fits together and shows that ethylene oxide and cyclopropane can be regarded as formed from CH₂ groups the carbon atoms of which are in a state of hybridization close to that of ethylenic carbon atoms. It is this most significant conclusion that a successful theory of these molecules has to explain and the implications of which have to be drawn out.