Photochemistry of 2-cyclopropylstyrene and of 5-phenylpentene from different vibronic excited states

Chang-Dar David Ho, Purdue University

Abstract

The cyclopropylcarbinyl radical rearrangement has been used to probe the photochemistry and photophysics of S2 and S1 vib in 2-cyclopropylstyrene (2CPS) in solution and in the gas phase. Solution phase excitation gives no photochemistry. Population of S2 with 254 nm excitation in the gas phase produces a ring expansion product 1-phenylcyclopentene (1PCP), which is analogous to that observed from cyclopropanated indenes. Cyclopropane ring opening-hydrogen shift products are also observed. All these products derive from the singlet manifold. A comparison with the results of the indene studies suggests that the twisted S1 state accounts for the formation of the photoproducts. Photochemistry from either S2 or S1vib of 2CPS is also governed by the ground state conformations of the vinyl cyclopropane rotamers. The photochemistry of 1PCP has also been studied in solution and in the gas phase. The S2 excitation in solution gives hydrogen shift and self redox products. Direct population of S2 in the gas phase lead to a phenylvinyl cyclopropane and trace amounts of the solution phase photoproducts is attributed to ring opening of a cyclopentene “diradical”. The second part of this thesis describes the gas phase photochemistry of 5-phenylpentene (1). In addition to meta-cycloadducts analogous to those observed in solution, population of S1vib in the gas phase gives several products, the relative amounts of which depend on quencher gas pressure but not on excitation wavelength. A [1,5] hydrogen shift product from the major meta-cycloadduct is also formed in the absence of a quencher. A unique ortho-cycloadduct of 1 is formed in a narrow range of quencher gas pressures.

Degree

Ph.D.

Advisors

Morrison, Purdue University.

Subject Area

Organic chemistry

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