Molecular-orbital realizations of the bent-bond model: Spiranic derivatives of cyclobutanone

In the frame of our studies on small-ring compounds, we deal here with structures in which a three-membered ring and a carbonylated four-membered ring are fixed in close proximity. The theoretical approach is through an allvalence electron semiempirical method. The experimental background, based on results of other workers, comprises mainly UV and IR spectral data. The main topics to be discussed are: charge-donation and charge-transfer from the 3-ring, hypsochromic and bathochromic shifts of electronic transitions related to the carbonyl, direct substituent effects on the carbonyl stretching frequency, and the across-ring interaction in cyclobutanone.Part XII in series. For previous papers, see Refs. [1, 2].