Question - Head-to-tail Polymerization Of Propylene Is Observed With The [cp2zr(r)]+ Catalyst. Explain This Result On The Basis Of Molecular-level Interactions.
Answer -
Each incoming propylene molecular orients with its methyl group in toward R, rather than out toward cp, in order to avoid unfavorable contacts with the bulky cp's. When the R group migrates to propylene, it migrates to the closer olefinic carbon, which is always the one bearing the methyl group (the "b carbon").