Solvent effects on the keto-enol equilibria of ethyl acetoacetate, acetylacetone, ethyl cyclopentanone-2-carboxylate, and methyl 4-metliylcyclopentane-1,2-dione-3,4,5-tricarboxylate have been st~idied by ultraviolet spectroscopy. The extent of enolization is mainly determined by the stabilization of the keto form by local association with polar or protondonating solvent molecules, just as in the case of n -+ T* transitions and infrared stretching frequencies. Solvent effects on infrared spectra reveal useful infornlation regarding the characteristic Ireq~iencies of the tautomers.Keto-en01 tautomerism has been investigated extensively by ultraviolet (I), infrared (2), and n.m.r. (3) spectroscopy. Keto-en01 equilibria are extrenlely solvent sensitive and the proportion of en01 form is found to be much greater in non-polar solvents such a s cyclohexane than in polar solvents such as alcohol or water. This is probably due to the stabilization of tlie lteto for111 by polar solvents through local association. Recently in this laboratory we have investigated the solvent effects on the n -+ a" transitions of several cliromophores and have evaluated contributions from different factors (4). These studies clearly indicate that solvent effects on the n -+ a" transitions are nlainly controllecl by local association between the solute and the solvent nlolecules and tliat the magnitude of tlie solvent blue shifts are determined by the polarity and/or proton-donating ability of the solvents. Studies of the solvent effects on infrared group frequencies have also shown tliat local association is an important factor in the determination of the solvent shifts (5). I t was consiclered interesting to sj~ste~natically investigate the lteto-en01 equilibria of a few systems in several solvents and correlate the observed effects with the solvent effects on the 7% -+ a:Qransitions and the stretching vibration frequencies of carbonyl groups. We have now studied the lteto-en01 equilibria of ethyl acetoacetate, acetylacetone, ethyl cyclopentanone-2-carboxy!ate, and methyl 4-~nethylcyclopentane-l,2-dione-3,4,5-tricarboxylate (I) in solvents of varying degree of polarity or/and proton-donating ability. EXPERIMENTALCommercial samples of ethyl acetoacetate and acetylacetone mere ~ised after suitable purification. Ethyl cyclopentanone-2-carboxylate was prepared by the procedure described in Orgaltic Syntheses (6) and methyl 4-metl~ylc):clopentane-l,2-dione-3,4,5-tricarbosylate was prepared according to the method of Ch~lang and M a (7). All the solvents were purified and fractionated before use.Ultraviolet absorption spectra were recorded with a MiIger U\,ispek, model H 700, spectrophotometer. Thc infrared spectra were recorded with a I'erkin-Elmer infrared spectrometer, model 137, with sodium chloride optics.Percentage of the en01 form was calculated from the extinction coefficieilt in the ultraviolet spectrum using the formula 1 0 0 (~~/~~) , where 6, is the observed molar extinction coefficient and s, the assumed value for the chromo...

Several new 4-amino (or hydroxy) 5-substituted pyrimidines are prepared by the reaction of trisformylaminomethane with various substituted acetonitriles, acetamides, and corresponding esters, and the reaction results are discussed.

'The 71 + as transition of the carbonyl group has been st~ldiecl in solvents of varying degree of polarity arid hydrogen-bonding ability, in a number of aliphatic carbonyl derivatives. Evidence for hyperconjugation of the alkpl groLrps in the electrorlically excited states of molecules has been presented.

No abstract

1,2-rlicyano esters show an absorption band around 245 mp in alcoholic solutions which is not found in non-polar and other polar solvents. This anolnalous behavior has been found to be due to the unusual solvent clepenclence of the equilibrium between the keto ancl el101 forms. The intensity of the absorption band in alcoholic solutions decreases with increase in concentration of the 1,2-dicyano ester, indicating association of the en01 form. The keto-enol equilibrium is also found to be sensitive t o the substitucnt R of the alcohol ROM. INTRODUCTIOS

No abstract

No abstract

The near-ultraviolet absorption spectra of polyphenyl derivatives of the IVb and V b elements have been studied in detail. In the case of the triphenyl derivativesof the Vbelements, the unshared p-electrons on the central atoms interact strongly with the ?r-orbitals of the benzene rings. When the central atoms do not possess unshared electrons a s in the case of the derivatives of the IVb and the pentavalent Vb elements, there appears t o be no such resonance interaction. The Hammett reactivity constants of the para-and meta-trityl, triphenylsilyl, and triphenylgermanyl groups are estimated to be close t o zero. However, the reactivity constant of the triphenylsilyl group in the para position of phenol is estimated t o be about 0.30. The infrared spectra of the phenyl derivatives of the IVb and V b elements show smooth trends due t o mass effects of the central atoms, in the C=C skeletal, C-H out-of-plane, and other vibrations. The absorption frequencies which are assigned t o the phosphorus-phenyl and silicon-phenyl bonds in the literature d o not appear t o be unique for these linkages.