Ethanes, fragmentation

This equilibrium was first studied by Cope et a .54 in 1952. The Gibbs energy difference is small and the rate of interconversion slow at room temperature. Huisgen et al.55 examined the influence of variations of the ethane fragment on the position of the equilibrium. Attachment of a tricarbonyliron moiety apparently causes stabilization of the bicyclo[4.2.0]octadiene system,56 whereas with tricarbonylmolybdenum the monocyclic isomer is isolated as its metal complex.57... 

Ring closure to cyclobutanes via valence isomerization of cycloocta-l,3,5-trienes is also possible when carbonyl functions are present in the ethane fragment. Thus, reaction of cyclohepta-2,4,6-trienone (tropone) with diazopropane gives 8,8-dimethylcycloocta-2,4,6-trienone (16, R = H), which rearranges quantitatively to 8,8-dimethylbicyclo[4.2.0]octa-2,4-dien-7-one (17, R = H).67... 

The success of the theoretical treatment of the angular dependence of 3J in an ethane fragment has served as the rationale for empirical calculations of the angular dependence of 3Jab and JM in the allylic system I. 

These are discussed in (B-71MS4). Oxirane itself shows a strong molecular ion peak and a slightly stronger base peak at mje 29 (CHO ) due to isomerization to ethanal and loss of a methyl radical. Substituted oxiranes tend to show only weak molecular ion peaks, because of rearrangement and fragmentation. 

The most stable of all alkyl cations is the tert-butyl cation. Even the relatively stable tert-pentyl and fen-hexyl cations fragment at higher temperatures to produce the tert-butyl cation, as do all other alkyl cations with four or more carbons so far studied. Methane,ethane, and propane, treated with superacid, also yield ten-butyl cations as the main product (see 2-17). Even paraffin wax and polyethylene give the ten-butyl cation. Solid salts of frrf-butyl and rerf-pentyl cations (e.g., MeaC" SbFg ) have been prepared from superacid solutions and are stable below -20°C. ... 

The sunuhaneous double Diels-Alder addition of l,l-bis(3,5-dimethylfur-2-yl)ethane (8) with a biS dienophile such as diethyl ( , )-4-oxohepta-2,5-diene-1,7-dioate was proposed as new, asymmetric synthesis of long-chain polypropionate fragments and analogues <96TL4149>. 

Sources of catalytically active palladium(O) typically arise from ligand dissociation from coord-inatively more saturated Pd° complexes871-880 or from reduction of a Pd11 species.353,881 Another route to catalytically active (P—P)Pd fragments is the dissociation of the dinuclear complexes [(//-P—P)Pd]2.882 Complexes [(/r-dcpm)Pd]2 and [(/r-dtbpm)Pd]2 were obtained from the reductive elimination of ethane from dimethylpalladium(II) complexes (dippm = bis(diisopropylphosphino)methane dcpm = bis(dicyclohexylphosphino)methane dcpm = bis(di-t-butylphosphino)methane).883... 

The simplest hydrocarbon hydrogenolysis reaction is that with ethane which can yield methane as the sole reaction product. On the other hand, with larger molecules a range of reaction products is possible since the adsorbed reactant may fragment at more than one C—C bond and, furthermore, even if only one such bond is broken in the reaction of a given molecule, the reactant will often contain more than one stereochemically distinguishable type of C—C bond. 

First structurally known iodine derivatives of this kind were products from the iodination of l,3-dimethyl-4-imidazoline-2-selone,44 of 1,2-6z s-(3-methyl-4-imidazoline-2-selone)ethane,44 and of l,3-diisopropyl-4,5-dimethyl-4-imidazoline-2-selone.42 The fragments for the three compounds... 

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