Y traps

The crystallinity of the samples rather than the degree of branching determines the relative importance of the a and of the j3 and y peaks. The a traps exist in the crystalline regions of polyethylene, the y traps in the amorphous regions and the j3 traps possibly in or around the surfaces of the crystallites. 

The word trap also expresses the fact that these point defects can frequently capture electronic excitation energy. Other well-studied X traps are those of pyrene in anthracene, with a trapping depth of AE= 59 cm b Naturally, there are also triplet X traps, e.g. in 1,2,4,5-tetrachloro-benzene, with AE = 21.3 cm . Host molecules can also act as X traps when they are perturbed not by foreign molecules but by a specific structural defect. Occasionally, in the literature a distinction is made between X and Y traps, depending on whether the lattice perturbation is caused by a structural defect in the crystal (Y trap) or by a foreign molecule (X trap). Plastic deformation of crystals can also produce discrete trapping states, for example in... 

Recent advances in each of the four Pd-catalyzed linear diene dimerization modes (Scheme 2 dimerization without trapping dimerization with incorporation of protic H—Y trapping reagents dimerization with incorporation of silanes or disilanes and... 

C. DIENE DIMERIZATION WITH INCORPORATION OF A PROTIC H—Y TRAPPING REAGENT... 

C.viii. Amines, Amides, Imides, and Sulfonamides as the H—Y Trapping Reagents Intermolecular Diene Dimerization... 

C.xi. Doubly Activated Methylene and Methines (C—H Acidic Compounds) as the H—Y Trapping Reagent Inter- and Intramolecular Diene Coupling... 

A number of types of carbon nucleophiles participate as protic H—Y trapping reagents in Pd-catalyzed linear diene dimerization. Among these, doubly activated methylene and... 

The following discussion is organized according to the nature of the R R )C=Y trapping reagent employed aldehydes and ketones, imines, and carbon dioxide and isocyanates. 

Phenylhydrazones exhibit another mode of reaction (Scheme 65). The reaction of butadiene with the phenylhydrazone of acetaldehyde 204 (1 mol % (Ph3P)4Pd, THF, 110 °C, 24 h) affords a 2 1 mixture of 205 and 206 (86%). A small amount of the protic (H—Y) trapping prodnct was also observed. The formation of 205 can be rationalized by addition of the phenylhydrazone in the fashion of a R (R )C=Y-type electrophile to a palladacycle in an Sgs fashion to 208 followed by hydride transfer to 209. Rednctive elimination conld acconnt for the formation of 205. Thns, 206 could be formed via a similar pathway, by addition of the phenylhydrazone in an rather than fashion. The proposed hydride transfer invoked to rationalize the formation of the observed products offers interesting possibilities and appears worthy of further investigation. Phenylhydrazones derived from propanal, acetone, and methyl ethyl ketone behave similarly (60-95% yield), although the ratio of 205/206 and the proportion of the protic (H—Y-type) trapping product vary. 

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