7-Methylenebicyclo[2.2.1] hept-2-ene and its derivatives are unusual in that the two double bonds are crossed. In contrast to the behaviour of most non-conjugated dienes toward palladium(ii), these dienes do not form stable chelated diolefin complexes. Instead, in solvents of low polarity, halogen-bridged dimeric 2-37-{ (bicyclo-[2.2.1]hept-2-en-7-yl)methyl) chelates are formed, in which C( 7) is bound to either CI. Br, or M e 0 (the latter if methanol is present in the reaction mixture). In the absence of methanol, the very fast overall reactions involve trans-addition of palladium and halogen to the exocyclic olefin, with co-ordination of the remaining double bond. The trans-addition must occur either by an ionic or a bimolecular path. In any event the facility for transhalogenopalladation observed here suggests that cisand trans-halogenopalladations of organic substrates may in general be competitive.CHLOROPALLADATION of unsaturated organic substrates is an important reaction in organopalladium chemistry.

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Molecular Structure of Dichloro (5-methylenecycloheptene) platinum (II)."In-Plane" Coordination of the Exocyclic Olefin Sir:The geometric requirements of olefins coordinated to Pt(II) have been of considerable recent interest. In two publications in this journal, Hoffmann and co-workers have utilized extended Hückel theory, first to model olefin insertion into Pt-H bonds,1 and second to model olefin rotation about the Pt-olefin bond axis.1 2 Thorn and Hoffmann1 concluded that the olefin "insertion" process in c/j-L2Pt(H)(olefin) proceeds with the lowest activation barrier when the olefinic carbons, Pt, and ligated hydrogen all lie in the square plane of coordination. It was noted that such a coordination geometry has not been observed to date in stable d8 square-planar olefin complexes.3 In the second paper, Hoffmann and co-workers concluded that the olefin prefers to bind perpendicular to the coordination plane, primarily as a result of unfavorable steric interactions with the cis ligands in the "in-plane" orientation.4 This view was presented earlier by Lewis and co-workers,5 as well as by Ziegler and Rauk.6 We have been interested in the synthesis of stable "in-plane" coordinated olefins for many years. We have reported7 our results

Proton acids and bases occupy a position of central importance in science majors' general chemistry courses. Their importance is not only emphasized in the lecture portion, but a good deal of laboratory time is often devoted to studying acid-base systems. Generally the laboratory, regardless of the manual used, consists of the same experiments: a) measuring the pH of a variety of substances (apple juice, coffee, etc.); b) determination of the GEW of an unknown acid by titration;

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