ISSN:
1042-7163
Keywords:
Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Using 13C-chemical shifts as a probe for the electronic environment of carbon centers, triphenylphosphoniomethanide, the model case of a “reactive” phosphorus ylid, was found to have much more zwitterion than PC double bond character (resonance structure 1a being dominant). Triphenylphosphonio-propenide (“triphenylphosphonium-allylid”), a “moderated” ylid, accumulates electron excess mainly at the α-carbon atom (resonance structure 6a being dominant) whereas triphenylphosphonio-ethenoate (formyl-methylene-triphenylphosphorane) and other “stabilized” ylids carry roughly equal fractions of negative charge at the α-carbon and the oxygen atom (resonance formulas a and b being of comparable importance). The one-bond C,H coupling constant of triphenylphosphonio-methanide (1) argues against a perfectly planar ylid center. The three-bond P,C coupling constants permit the assignment of endo- or exo-configurations to ylids having an allyl-type side-chain.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hc.520010205
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