Solvent Increment Not Solvent Correction A Suggested Modification in the Procedure of Calculating Wavelength of Maximum Ultraviolet Absorption of a$-unsaturated Aldehydes and Ketones Mohammad lsmail Qureshi Garyounis University, P.O. Box 9480, Benghazi, Libya
The wavelength of maximum ultraviolet absorption in ethanol solution hz':; of ap-unsaturated aldehydes and ketones can be calculated fairlv accuratelv bv nsine the emnirical considerably with the solvent&rity, it is ne'essary to take in a into account the solvent effect when calculating A,, solvent other than ethanol. This is now done by subtracting a solvent correction ualue from the calculated
hsY1"e"t I"ax =X
Z - solvent correction
The present procedure of calculating X:pthas an unnecessary element of confusion. This confusion can be removed simplified hy using soluent Inand the calculation of X ","? crement to account for the solvent effect. The solvent increments for the various solvents can be derived from their solvent correction values by changing signs (+ or -). It would be possible then to add the solvent increment just like the increments for the structural features present within the molecule. The use of this method can he explained, and its advantage over the existing procedure elaborated, by the following calculation of A"',: of mesityl oxide (MezC=CHCOMe).
Parent value for an acyclic aSunsaturated ketone Increment for two B-alkyl groups = 2 X 12 Solvent increment for water
= 215 nm = 24 nm = +R nm =-
The calculation of X E P h y this modified procedure would require enlargement of the currently used table of rules (6,7, 8) to include the following solvent increments. Soluent increment, for
ethanol methanol dioxane chloroform diethyl ether Water hexane eyelohexane Literature Cited (1) Woudward,R. B., J A m e i Chem Soc.63.1123 (1941).
(2) W0odward.R. B., J. A m s i Chem Soc.64.72.76 (19421. (31 Fieser, I.. M., and Fieser, M.."Naiural Products Related to Phenanthrene.l'~~inhold. New York, 1949, n. 184. (4) Fieser, L. M.. and Fieser, M., "Steroids."Reinhold, New Yark, 1959 ( 5 ) Scott, A. I., "Interpretation of the Ultraviolet Spectra of Natural Products: Pergamon Press, Oxford. 1964. ( 6 ) Williams, D. H.. and Fleming, 1,"Spectmscnpic Methods in OrganicChemistry.l'2nd Ed.. McCraw-Hill, London, 1973, p. 18. (7) Cresswell. C. J., Runquisi. 0. A , and Campbell, M. M.. "Spectral Analysis oiorganic Compounds-An lntrnductnry Proprammed Text." 2nd Ed., Longman. 1972, p. 46. (81 Silverstein. R. M., Barsler. C. C., and Morrill, T. C.. "Spectrometric Identification of Organic Compuunds,"3rd Ed., John Wiiey, NewYork, 1974, g. 24&
Volume 60 Number 2
February 1983
149
