Site-selective reaction of Cl + propene in solid para -hydrogen: Formation of 2-chloropropyl radicals

The reaction of chlorine atoms with propene in a solid para-hydrogen matrix has been studied using infrared spectroscopy. For the Cl atom addition reaction, we find that the only observed isomer of the chloropropyl radical is the 2-chloropropyl and not the 1-chloropropyl radical, indicating that the addition of the Cl atom to the carbon-carbon double bond of propene occurs primarily at the central carbon atom. This is in sharp contrast to the generally accepted mechanism in organic chemistry and in gas-phase reactions in which the addition to the terminal carbon atom is greatly favored. This unique selectivity is possibly due to steric effects in solid para-hydrogen, in which the complex of Cl₂ and propene are positioned so that the reacting Cl atom is closer to the central versus the terminal carbon atom of propene. One might be able to make use of this unique property to perform selective chemistry.