Abstract: The reaction of INCO with a number of olefins has been studied with a view toward elucidating electronic and steric influences in the addition. The stereospecific addition of INCO to cis-and trans-Zbutene and 8-deuteriostyrene is consistent with the intermediacy of a three-membered iodonium ion. A definite dependency on steric factors is evidenced by the It- Bu regiospecificity in the INCO addition to t-butylethylene. The structure proof in these ...