18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The purpose of this approach was to obtain valid judgements on preparations in which the unavoidable impurities, though reduced to a minimum, did not have to be completely eliminated. This is essential, since absolute olfactive purity is not attainable. Preparations which show only one peak on glc under conditions of maximum sensitivity of the instrument are virtually unattainable, particularly with compounds with useful frag- rance qualities, which are often associated with materials of lesser chemical stability. When one considers that "glc purity" even if attainable, would not guarantee the absence of undetected trace amounts of impurities which could influence the known greater analytical power of the human nose, the task of preparing standards of absolute odor purity clearly remains beyond our ability. It is the olfactory analysis of this series based upon pairings from four presented materials which comprises the essentially novel approach to the question of chiral odor discrimination. The evaluation method used permitted a statistical analysis of these odor judgments by both expert and lay panels. A priori, three possible results were possible: (1) The panels would render judgements close to random selection, thus showing no significant differences. This would mean only that the impurities did not dominate the judgments. (2) The panels would select (d-l,/-1) and (d-2, 1-2) as matching pairs. This would mean that the impurities due to the synthetic methods were the main cause of the odor differences, and would render the whole research meaningless. (3) The panels would select (d-l, d-2) and (l-l, 1-2) as pairs, at least in some of the five comparisons. The more such (d-l, d-2) rs. (/-1, 1-2) pairings and the greater the statistical weight of these, the more convincing the conclusion that dextro and laevo isomers can indeed be distinguished by odor. PROCEDURE Preparation of test compounds The starting materials were dextro-alpha-pinene and laevo-beta-pinene from Greek and American turpentine oils respectively. They were of approx- imately 98-99% glc purity and were over 90% optically pure. The impurities were the isomeric terpenes known to be present in all pinenes and not separable even by glc trapping.

ODOR AND OPTICAL ACTIVITY 19 /-[l-pinene was converted to/-a-pinene by Pd/C catalysed isomerization (6), and d-a-pinene was converted to d-[l-pinene, not otherwise available in high optical purity, by boron hydride isomerization (4). The four pinenes, d- and l-a, and d- and 1-• were then each prep-trapped to 98-99% purity. It is important to note that this trapping procedure, while not yielding absolutely glc pure pinenes, was able to separate a- from [I-pinene with no difficulty, so that any impurities remaining in the 1-a and d-• were not the ones originally present in the d-a and 1-•. Thus there were essentially four discrete starting materials, and the impurities intro- duced in subsequent operations and not removed in the final purifications would all tend to make (d-l,/-1) and (d-2, l-2) pairs. The a-pinenes were epoxidized and isomerized to trans-pino-carveol. The [I-pinenes were oxidized directly to pinocarveol. Each route gave substantial by-products, known to be partially myrtenal and pinocarvone in the direct oxidation procedure, unknown but different in the epoxide isomerization. The pinocarveols were approximately 90% pure after distillation. Compound Myrtenal diethyl acetal Table I. Optical rotation (laid) of test compounds -39.3 -37.0 -14.3 trans-Pinocarvyl propionate -14.0 Myrtenal -11.1 i -15.2 Pinoacetaldehyde -40.6 -44.6 trans-Pinocarveol , +72.2 +71.2 Hydroxy citronellal [ --10.8 d-1 +36.5 +12.9 +12.5 +43.4 -69.4 +10.7 d-2 +38.5 +14.1 + 5.8 +37.7 -71.0 +11.9' *ex Citronella oil The test substances were made from these pinocarveols as shown in Fig. 1. In each case, at least one rigorous purification step was used along the way. Still, the final glc purifies were usually in the 98-99% range, although, as might be expected, d- 1 and l- 1 had similar glc patterns differing in general from the similar patterns of d-2, 1-2. Analysis of all intermediates and final products confirmed that optical integrity was maintained throughout except in the case of myrtenal, in which the rotations, although of correct sign, deviated somewhat from literature values in several of the samples (Table 1). The materials were blottered to the same depth from 50ø/0 penfane solutions and presented to each panelist in groups of four coded, randomly