This project is being supported by the Organic and Macromolecular Chemistry Program. A variety of novel structure-types and novel chemical reactions are being investigated which include pentacoordinate organosilicon compounds, strained-bridged aromatic compounds, and unusual carbenoid and radical containing organic compounds. Study is being made of (1) synthesis and the chemistry of novel single-atom peri-bridged arenes and their derivatives, (2) the products, stereochemistry and mechanisms of pentacoordinate addition-rearrangement-ejection reactions of alpha-haloalkylsilanes with nucleophiles, (3) generation and the behavior of metallized carbenes, carbynes and alpha-diazo radicals and (4) carbenic capture and aromatic substitution and expansion processes involving conjugative alpha-elimination and addition.