Methylene groups ethylene derivs. from

The decay of the tetramethylene diradical derived from 2,2,5,5-t/4-cyclopenta-none is much slower than seen for the C4Hg diradical. Both principal decay modes, fragmentation to two ethylenes and ring-closure to cyclobutane, may be dependent dynamically on torsional motions of the terminal methylene groups. 

The fluorescence properties of 2,2-diaryl-substituted l-(9-anthryl)-ethylenes 87c-e differ markedly from those of 87a, b by a decrease in the quantum yields of emission, and by the loss of vibrational fine structure of the emission spectra, which is associated with a dramatic increase of the Stokes shifts. For the 2,2-diphenyl derivative 87c in cyclohexane solution, the quantum yield is 0.29, and the Stokes shift is 5600cm-1. For 9-anthryl-ethylene 87e, in which the formal conjugation has been extended by a terminal methylene group, the quantum yield in cyclohexane is as low as... 

For historical reasons, there are a few alkenes whose names are firmly entrenched jn common usage but don t conform to the rules. For example, the alkene derived from ethane should be called ethene, but the name ethylene has been used so long that it is accepted by lUPAC. Table 6.1 lists several other common names that are often used and are recognized by lUPAC. Note also that a =CH2 substituent is called a methylene group, a H2C=CH substituent is called a vinyl group, and a H2C=CHCH2- substituent is called an allyl group ... 

Synthesis of monoorganomercury compounds from ethylene derivatives and active methylene groups via acetoxymonoorganomercury compounds... 

The polymers formed from symmetric monomer units, such as polyethylene, (CH2CH2) and polytetrafluoroethylene, (CF2CF2) are an exception to this notation. Although the simplest repeat units are the —CHj— and —CF2— groups, we show two methylene groups and two difluoromethylene groups because they originate from ethylene (CH2= H2) and tetrafluoroethylene (CF2= F2), the monomer units from which these polymers are derived. 

Alkyhdene derivatives of titanium and of phosphorus catalyse methylene exchange between olefins. Although exchange of CH2 groups is not useful for synthesis, these systems provide insight into the mechanisms of alkylidene exchange, a basic step in conventional metathesis. Titanacyclobutenes have been isolated from reactions of acetylenes with methylene-titanium complexes but titanacyclobutanes, the assumed intermediate for the case of olefins, have not been isolated. Bis(cyclopentadiene)titanacyclohexane decomposes to produce ethylene as the major product apparently via a-C-C bond cleavage. ... 

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