The basicities of 14 diaryl ketones have been determined. Except for 4,4'-bis(dirnethy1-amino)benzophenone, which protonates on nitrogen, the ~K B H + values range from -4.19 for 4,4'-dihydroxybenzophenone t o -10.12 for 4,4'-dinitrobenzophenone. The basicities are not correlated well by either r or g+ substituent constants and it is believed that this is due either to a variation in the degree of rotation (and hence conjugation) of the two aryl rings or to a departure of carbonyl basicities from the conventional acidity scale based on ammonia bases. The effect on the basicity of joining the ortho positions b y bridges of various sizes has also been determined and the results are discussed in terms of steric and electronic effects.Previous work in this laboratory has been concerned with the protonation of very weakly basic groups such as carbonyl ( I ) , carboxyl (2, 3), and carboxamido (4, 5). L2' e now wish to report the basicities of two series of diaryl ketones. In one series the para or meta substituents in benzophenone are varied and in the other the angle of the aryl rings with the carbonyl group is varied by means of ortho-ortho bridges.The basicities of benzophenone and anthrone have been previously measured by Handa and Koboyashi (6) and those of benzophenone and some of its alkyl derivatives by Fischer, Grigor, Packer, and Vaughan (7). RESULTS A N D DISCUSSIONThe basicities and the ultraviolet spectral data for the diaryl ketones are given in Table I. Unlike the series of monoaryl ketones and aldehydes (I) whose basicities correlate quite well with the modified Hammett substituent constants, u+ (8), the present series (compounds I to VIII) does not give a very satisfactory fit with any of the parameters commonly used in linear free energy correlations. This may be due to the presence of two potentially conjugating rings each of which can rotate and whose actual degrees of conjugation may vary considerably with the identity of the para substituents. Another possibility to be considered is that carbonyl compounds are not following the conventional Haminett acidity function, Ho, which is based on protonation of amine bases (9, 10).The satisfactory correlations with u+ previously observed for benzaldehydes and acetophenones do not cover nearly the range of acidities spanned by the benzophenones. Recent work suggests that the anomalous ionization curves often obtained with carbon)-] bases are due less to solvent effects on spectra than to the compounds' ionization not following the function Ho (9). I t should be pointed out in this connection that most of the

Dicyclohexylurea-018 containing 78% oxygen-18 has been prepared. The amide I and I1 bands in this molecule are located a t 1611 and 1575 cm-1 respectively compared to 1628 and 1575cm-1 in ordinary dicyclohexylurea(KBr disk).Thus the amide I band(carbony1 stretching) undergoes the expected shift to lower frequency on isotopic substitution. The p-toluenesulphonate salt of dicyclohexylurea has been prepared and been found to have a band a t 1669 cm-1 commonly attributed to carbonyl stretching in amide salts. This band, however, undergoes no isotopic shift and is clearly not due to a carbonyl stretching motion. This result casts doubt on the infrared evidence supporting N-protonation of amides.