Cyclobutanone, absorption spectrum

The ultraviolet absorption spectrum of cyclobutanone has been reported only in heptane solution (24). The absorption is appreciably shifted towards shorter wavelengths as compared to cyclopentanone, but shows a similarly banded structure. 

The ultraviolet absorption spectrum of cyclohexanone reflects the n jt transition common to all carbonyls see figure IX-E-1. The data derived from gas-phase measurements of the cross sections for cyclohexanone from two different research groups [National Center for Atmospheric Research (NCAR) and Ford Scientific Laboratories (Ford)] are in reasonable agreement (Iwasaki et al., 2008). The cyclohexanone cross sections as measured in cyclohexane solution by Benson and Kistiakowski (1942) had indicated seemingly low values (cross sections shown here is significantly less than those observed for cyclopropanone, cyclobutanone, and cyclopentanone, and in fact, all other carbonyls considered in this work. It is not obvious why these significant differences exist in the probability for the n -> 7T transition for cyclohexanone and that of the other cyclic ketones and most other carbonyl compounds. Theoretical studies will be important in defining the reasons for these differences. 

The purity of cyclobutanone was checked by gas chromatography on a 3.6-m. column containing 20% silicone SE 30 on chromosorb W at 65°. The infrared spectrum (neat) shows carbonyl absorption at 1779 cm. - the proton magnetic resonance spectrum (carbon tetrachloride) shows a multiplet at 8 2.00 and a triplet at S 3.05 in the ratio 1 2. 

Ketones. Normal acyclic ketones can be recognised by a strong band at 1720 cm -1 (e.g. see the spectrum of 4-methylpentan-2-one, Fig. 3.28). Branching at the a-carbon atoms results in an increase in the C—CO—C bond angle and this results in a decrease in frequency of absorption from the normal value of 1720 cm -1 to, for example, 1697 cm -1 as in di-t-butylketone. Conversely as the C—CO—C bond angle is decreased the absorption frequency rises, thus cyclo-pentanone and cyclobutanone absorb at 1750 cm-1 and 1775 cm-1 respectively. 

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