CROSS-ADAPTATION BY STRUCTURAL ANALOGS 371 a manner described previously (11,14). The methyl esters of 3M2H were subsequently made as follows: A mixture of approximately 3:1 E- and Z-3-methyl-2-hexenoic acids (1.0 gm, 7.8 x 10 -3 mol) was dissolved in methanol (25 ml) under N 2. Concentrated sulfuric acid (0.5 ml, 9.4 x 10 -3 mol) was added, and the reaction mixture was brought 5 ? 0 8 6•• 0 8 6 4 2 9 H H 7 2 9 E-Isomer Z-Isomer 3-Methyl-2-hexenoic acid (3M2H) 5 7 8 •4 0 8 5• 6 • 10 o o / 7 2 9 E-Isomer Z-Isomer Methyl esters of 3-methyl-2-hexenoic acid (ME3M2H) E-Isomer 7 0 8 6• Z-Isomer Methyl esters of 3-methyl-3-hexenoic acid exo-3-methylidine-methyl-hexenoate Figure 1. Chemical stimuli used in the present study. On the left are the (E)-isomers, on the right, the (Z)-isomers.

372 JOURNAL OF COSMETIC SCIENCE to reflux for 1.5 h. Reaction progress was monitored by aliquot workup and gas chro- matography (Perkin-Elmer 990 GC 30-m x 0.52-mm (i.d.) column with 1.0-1a coating of Stabilwax [Restek, Bellefonte, PAl held at 100øC for 17 minutes and programmed at 6øC per minute to 200øC). The reaction mixture was poured into chilled water. Dichloromethane was added, and the aqueous phase was basified to pH 8 with sodium bicarbonate. The organic compo- nents were extracted into dichloromethane (2 x 25 ml) and distilled. Separation of the acids from the esters was accomplished by column chromatography through silica gel with dichloromethane doped with 1% NH4OH as eluent. Analysis of the acid-free ester mixture was performed by combined gas chromatography/ mass spectrometry (GC/MS Finnigan/MAT 4510) utilizing the same chromatographic conditions described above. This analysis indicated that in addition to the desired methyl esters, a small amount of three other products derived from double-bond mi- gration to the 3- and exo-position were present. These data indicated that the following percentages of methyl esters were present: E (56.7%)-and Z (17.6%)-3-methyl-2- hexenoates and the remaining 25.7% consisting of the E, Z-3-methyl-3-hexenoates (16.3%) and exo-3-methylidine-methyl-hexenoate (9.4%). We did not attempt to fur- ther separate the isomer mixture and used it as the cross-adapting stimulus. STIMULI PRESENTATION Odorants were diluted in odorless, light, white, mineral oil and presented in 270-ml polypropylene squeeze-bottles with plastic, flip-top caps. Each bottle contained 10 ml of the odorant/mineral oil solution. A twelve-step binary dilution series was prepared for each odorant. Initially, 20 mg of each odorant was diluted in 20 ml of odorless, light, white, mineral oil to yield a 1 mg/ml (0.1% w/v) solution with molar concentrations of 7.81 mM for 3M2H and 7.04 mM for ME3M2H. The dilution scheme for each odorant was the same, ranging from 1.0 x 10 -• w/v (step 12) to 4.88 x 10-5% w/v (step 1). Subjects were tested in two 30-minute sessions using a procedure described previously (3,9,10). Briefly, a forced-choice, staircase procedure was used at the beginning of each session to equate intensities of the test stimuli for each subject. A two-minute rest was imposed following perceptual matching. Subjects then rated, using magnitude estima- tion, the intensities of step 10 of the adapting stimulus and the intensity-matched concentration of the other test odorant. Subjects assigned numerical ratings to each of these two stimuli twice. If the means of the magnitude estimates for each odor were dissimilar (greater than 20% discrepancy), the matching procedure was repeated. In this manner, initial magnitude estimates ensured that the two stimuli were perceptually equivalent for that subject. Thus, in a given session, the test odorants were step 10 of the odorant for adaptation and the concentration of the other odorant judged to be most similar in intensity by the individual subject the stimulus used for adaptation was a fourfold higher concentration (i.e., step 12) than the test stimulus. After making the initial magnitude estimates, subjects began to sniff repeatedly the adapting stimulus. Every 15 seconds during this adaptation period, subjects sniffed and rated a test stimulus between sniffs of the adapting stimulus. The test stimulus, either 3M2H or ME3M2H, alternated on sequential trials so that subjects made a total of 20