UV ABSORPTION BY SUNSCREENS 207 (8) R. Silverstein, G. Bassler, and T. Morrill, Spectrophotometric Identification of Organic Products, 3rd ed. (John Wiley and Sons, Inc., New York, 1974), pp. 231-258. (9) Note that A E = hv = hc/•., where v = frequency, •. = wavelength, c = speed of light and h = Planck's constant. Thus energy and wavelength have a reciprocal relationship, i.e., as energy in- creases, the wavelength decreases and vice versa. (10) J. March, Advanced Organic Chemistry Reactions, Mechanisms and Structure (McGraw-Hill Book Com- pany, Inc., New York, 1977), pp. 29-71. (11) A. I. Scott, Interpretation of the Ultraviolet Spectra of Natural Products (Pergamon Press, New York, 1964), p. 271. (12) Reference 5, pp. 242-286. (13) Shifts to longer wavelength are termed bathochromic or red shifts to shorter wavelength, hyp- sochromic or blue shifts. An increase in the extinction coefficient (intensity of absorption) is termed hyperchromic effect, and a decrease is hypochromic effect. (14) C. Rao, Ultraviolet and Visible Spectroscopy, 3rd ed. (Butterworth and Co. Ltd., London, 1975), pp. 162-182. (15) H. M. Hershenson, Ultraviolet and Visible Absorption Spectra (Academic Press, New York, 1956), pp. 1930-1954. (16) J. G. Grasselli and W. M. Ritchey, Atlas of Spectral Data and Physical Constants for Organic Compounds, 2nd ed. (CRC Press, Inc., Cleveland, 1975), Vol. II, III, and IV. (17) Reference 11, pp. 104-116. (18) R. T. Morrison and R. N. Boyd, Organic Chemistry, 3rd ed. (Allyn and Bacon, Inc., Boston, 1973), pp. 787-814. (19) S. Riegelman and R. Penna, Effect of vehicle components on the absorption characteristics of sun- screen components. J. Soc. Cosmet. Chem., 11, 280-291 (1960). (20) G. Groves, Evaluation of solar protective preparations, Cosmet. Perf., 90, 36-50 (1975). (21) B. Cumpelik, Spectral shift of lambda max of PABA in hydroalcoholic system, Van Dyke Technical Bulletin (Belville, New Jersey, 1977). (22) L. Paloympis, R. Nash, and N. Shaath, J. Soc. Cosmet. Chem., submitted for publication, 1986. (23) Reference 5, pp. 111-146. (24) A. Streitwiezer, Jr., Molecular Orbital Theory for Organic Chemists (John Wiley and Sons, Inc., New York, 1961). (25) Reference 14, pp. 118-127. (26) G. Groves, P. Agin, and R. Sayre, In vitro and in vivo methods to define sunscreen protection. Aust. J. Derre. 20, 112 (1979). (27) S. Kreps, Sunburn protection and suntan preparation, Amer. Perf. Cosmet., 78, 73-76 (1963). (28) E. Pines, A new technique to assess the sunscreen effectiveness, J. Soc. Cosmet. Chem. 29, 559-564 (1978). (29) B. Cumpelik, Sunscreens at skin application levels: Direct spectrophotometric evaluation, J. Soc. Cosmet. Chem., 31, 361-366 (1980). (30) R. Sayre, P. Agin, D. Derouches, and E. Marlowe, Sunscreen testing methods: In vitro predictions of effectiveness, J. Soc. Cosmet. Chem., 31, 133-143 (1980). (31) J. Vogelman, E. Nieves, J. Brend, R. Nash, and N. Orentreich, A spectrophotometric method determining relative SPF values of sunscreen preparation, J. Applied Cosmetol., 1, 1-11 (1985).