The stereoc hemistry of catenanes, knotted molec~lcs, and B.orromean rings is discussed. An augmentation of the Cahn-Ingold-Prelog conventlOn f

10), retrieved by the SSS system and of interest to the searcher, was missed by the RAPID strategy because the carbonyl group was not sought.

The addition of ethylene to isopropyl-and /-butyllithium, previously reported,3 occurs also with secbutyl-and cyclohexyllithium, but not with cyclobutyl-, phenyl-, benzhydryl-, or triphenylmethyllithium. An ether or an amine is a necessary catalyst; both are attacked by alkyllithiums, but not at the low temperatures (below -10°) of these experiments, where the addition of ethylene is still rapid. No other acyclic, unconjugated olefin approaches ethylene in reactivity. The /3-alkylethyllithium, which is formed quantitatively, has been characterized in each case both by carbonation to an acid-ketone mixture and by reaction with benzophenone to a tertiary alcohol whose methyl ether gives rise quantitatively in vapor chromatography to a 1,1 -diphenylalkene. The ethylenation of secondary and tertiary alkyllithium is a reaction of potential synthetic utility.The additions of alkyllithiums to conjugated unsaturated systems such as ,/3-unsaturated ketones, dienes, fulvenes, and styrenes, and also to alkynes, are well-known reactions of synthetic, and in some cases economic, importance. zz-Butyllithium also adds readily to the homoconjugated diene, norbornadiene.1•2 On the other hand, the addition of alkyllithiums to unconjugated carbon-carbon double bonds in hydrocarbon molecules has been observed in comparatively few cases.In 1953, Bartlett, Friedman, and Stiles3 reported that isopropyllithium (1) in ethyl ether at low temperatures adds ethylene at atmospheric pressure, yielding isopentyllithium (2) as the sole reaction product. Similar results were reported for /-butyllithium (3), which formed neohexyllithium (4). In each case the secondary or tertiary alkyllithium added ethylene rapidly under conditons where the primary alkyllithium was inert to ethylene.Primary alkyllithiums are ethylenated only under much more vigorous conditions. In 1950, Ziegler and Gellert4 reported that «-butyllithium in a hydrocarbon solvent adds ethylene at high pressure in an autoclave. Further addition of ethylene to the product yielded a linear polyethylene of low molecular weight.More recently it has been shown that «-butyllithium in the presence of a chelating tertiary amine, such as , , ',N '-tetramethylethylenediamine, will polymerize ethylene at 50 atm pressure and 100°to yield a linear polyethylene5'6 of high molecular weight.Apart from ethylene, the only isolated double bonds reported to undergo addition of organolithiums have been somewhat activated by strain. Mulvaney and Gardlund have reported7 that /-butyllithium adds to the unconjugated double bond of norbornene (5). This retí) G. Wittig and E.

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Chemical structure diagrams are considered as utterances in a written language. Two types of grammars are considered for this language: topological grammars which emphasize the connectivity of the diagrams and geometric grammars which emphasize the arrangement of the diagrams in a plane. The vocabulary associated with each grammar consists of entities like atomic symbols, numeric subscripts, and bond symbols. Examples are given of initialization, propagation, and terminalization rules from each type of grammar and of the application of such rules. The value of grammars for the validation of computer input and for generation of computer output are indicated. The hypothesis is presented that compact computer storage may become accessible via grammars.