A series of cycloalkanones with ring size (n = 4–10, 15) has been examined in the near ultraviolet region in a series of solvents covering a broad polarity range. The transition energies (ET) were plotted against the solvent polarity standard, Z (ref. 4). Cyclobutanone was found to have a n→ π*-transition with rather low sensitivity to solvent, and brief examination of two other cyclobutanones suggested that such low sensitivity may be characteristic of these rings. The transitions for the ketones with n = 5 through 10 correlate rather well with Z, and the correlation for cyclohexanone is so good that it can be used as a secondary standard of solvent polarity. It was found that the slope of the correlation for cyclopentadecanone, n = 15, was unexpectedly low. Low solvent sensitivity for the n → π*-transition of the C15-ketone was rationalized by postulating that the molecule tended toward “folded” conformations in polar solvents, but was “open” or “extended” in non-polar solvents. The C15-ketone absorption band obeyed Beer's law in all solvents.