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Reinvestigation of the acetone extract of the whole plant of Euphorbia tuckeyana yielded the new natural nor-triterpene 3β-hydroxy-9,19-cyclo-4,4,14α-trimethyl-5α-pregnan-20-one (1). Its structure was established based on spectroscopic data including one and two dimensional NMR both for proton and carbon assignments The known tetracyclic triterpenes butyrospermol (2), lanosterol (3), 24-methylenelanosterol (4) and the steroid stigmast-4-en-3-one (5), were also isolated and identified.

Only substances that have a molecular weight below about 400 and an appreciable vapor pressure at room temperature can be perceived as having odor. The spectrum of odorants is thus limited to relatively small, neutral organic compounds, including undissociated acids and nitrogenous bases.1 Relatively few organic acids are sufficiently volatile to contribute to natural aromas. Acetic (vinegary), propionic (goaty), butyric (spoiled butter), and lactic (sauerkraut) acids are odorous at relatively high concentration.

This article focuses on the main developments in polymers containing conjugated -HC=CH- bonds. It begins with oxidative coupling, which at the start of the 1960s evolved through various stages of polyaromatic and polyheteroaromatic synthesis to culminate in the production of electrically conducting polymers (polypyrrole, polythiophene, polyphenylene, etc.).

The main reactions of ketones and hydroperoxides to be expected on photo-oxidation of polyethylene are reviewed. The performance of various light stabilizers on outdoor exposure of polyethylene is compared. HALS used alone or in combination with benzotriazole-type UV absorbers show by far the best effect.

The complexity and inhomogenity of food aromas (see table 18, p. 58) lead to the assumption that the single aroma components must be formed by very different and specialized reaction mechanisms. The distribution into chemical classes provides little more information than defining the most important chemical groups or — as an exceptional case — the key classes. Comparing the lists of volatile compounds in food collected and summarized by S. van Straten et al. (1973, 1977), H. Maarse (1984, 1985) and H. Maarse and C. A. Visscher (1986), however, some similarities can be found. It may be surpising, for example, that some very simple aroma components have been identified in practically all foods. This is true for all saturated alcohols, aldehydes, and amines with up to six carbon atoms and the even-numbered fatty acids of short to medium chain length, as well as the first members of homologous series, for example acetone, 2.butanone, 2,3-butanedione (diacetyl), methyl formate, methyl and ethyl acetate or methyl mercaptan. Additionally, a lot of other components are also found in very different food items. The total number of aroma compounds identified is limited by such effects: nearly 4500 volatiles have been identified in food up to now, but this is a relatively small number compared with the fact that in every food item examined in detail between 100 and 600 components have been found. Considering this wide spread of aroma compounds within the broad field of foods and beverages, with their very specialized flavours, the question arises whether a typical aroma might be a consequence of different amounts of the same substances. Cocoa was earlier discussed as an example. Of the 310 aroma components identified by 1976, 260 were also found in other foods (W. Mohr et al. 1976). Might this fact be caused by the same, or similar, formation mechanisms?

Flavour is composed principally of the sensations of smell and taste, though the senses of sight, touch, and hearing interact with those of smell and taste. Whereas the sense of taste is relatively simple in having only four modalities—bitter, salt, sour, sweet (with perhaps astringent, soapy, and MSG-like)—the modalities of smell are still very much under discussion; the 44 qualities described by Harper et al.1 are a good summary of the current state of knowledge.

As has been seen, initial studies on the combustion of hydrocarbons were concerned with the effects of conditions such as pressure, composition, vessel temperature etc. As analytical techniques improved, it became clear that the product spectrum, particularly at fairly low temperatures, from any compound containing more than one carbon atom was very complex indeed. Further, ever since Semenov proposed the theory of degenerate branching to explain the observed phenomena in low-temperature hydrocarbon combustion, the search for the identity of the branching intermediate preoccupied many investigators. In this search, experiments were carried out in which possible intermediates were added to combustion systems, and various types of compounds claimed their supporters. It became the custom, therefore, to regard the multiplicity of hydrocarbons as producing a multiplicity of products and to stress the differences between combustion systems at high and low temperatures, rather than to seek similarities and connections.