Infrared absorption of trans-1-chloromethylallyl and trans-1-methylallyl radicals produced in photochemical reactions of trans-1,3-butadiene and Cℓ2 in solid para-hydrogen

Abstract

The reactions of chlorine and hydrogen atoms with trans-1,3-butadiene in solid para-hydrogen (p-H(2)) were investigated with infrared (IR) absorption spectra. When a p-H(2) matrix containing Cl(2) and trans-1,3-butadiene was irradiated with ultraviolet light at 365 nm, intense lines at 650.3, 809.0, 962.2, 1240.6 cm(-1), and several weaker ones due to the trans-1-chloromethylallyl radical, ●(CH(2)CHCH)CH(2)Cl, appeared. Observed wavenumbers and relative intensities agree with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++g(2d, 2p) method. That the Cl atom adds primarily to the terminal carbon atom of trans-1,3-butadiene is in agreement with the path of minimum energy predicted theoretically, but in contrast to the reaction of Cl + propene in solid p-H(2) [J. Amicangelo and Y.-P. Lee, J. Phys. Chem. Lett. 1, 2956 (2010)] in which the addition of Cl to the central C atom is favored, likely through steric effects in a p-H(2) matrix. A second set of lines, intense at 781.6, 957.9, 1433.6, 2968.8, 3023.5, 3107.3 cm(-1), were observed when the UV-irradiated Cl(2)/trans-1,3-butadiene/p-H(2) matrix was further irradiated with IR light from a SiC source. These lines are assigned to the trans-1-methylallyl radical, ●(CH(2)CHCH)CH(3), produced from reaction of 1,3-butadiene with a H atom resulted from the reaction of Cl atoms with solid p-H(2) exposed to IR radiation.

Photolysis and thermolysis of (iodomethyl)cyclopropane: Rapid ring opening of cyclopropylcarbinyl via heavy‐atom tunneling?

“…The experimental spectrum is in good agreement with the theoretical spectra of the ring opening product 2 as its two most stable conformers, cis-2 and gauche-2. In line with earlier theoretical investigations, [18,25] it was calculated that gauche-2 is only approximately 0.6 kcal mol À1 more stable than cis-2, thus both conformers are expected to contribute to the experimentally observed spectrum. While Brown et al had noticed a significant mismatch between the calculated spectra and their experimentally observed ones at e ν > 2800 cm À1 , [18] the most intense absorptions in the fingerprint region agree with the calculations rather well, though they only allow for a tentative assignment to either gauche-or cis-2.…”

Infrared spectra of free radicals and protonated species produced in para-hydrogen matrices

“…In the radical mechanism, the initial process involves addition of a Cl atom to the CQC bond to form chloroalkyl radicals, but the direct IR identification of these chloroalkyl radicals is unreported. We have investigated free-radical intermediates produced from the reactions of Cl atoms with C 2 H 4 , 63 propene (C 3 H 6 ), 64 trans-1,3-butadiene (C 4 H 8 ), 65 and benzene (C 6 H 6 ). 66 In all cases, Cl atoms were produced on irradiation of Cl 2 in solid p-H 2 with light near 365 nm from a light-emitting diode.…”

Infrared absorption of 3-propenonyl (⋅CH2CHCO) radical generated upon photolysis of acryloyl chloride [CH2CHC(O)Cl] in solid para-H2

“…[26][27][28][29][30] In this work, we have photolyzed a CH 2 CHC(O)Cl/p-H 2 matrix at 3.2 K with laser light at 193 nm and observed absorption lines ascribable to 11 fundamental vibrational modes of 3-propenonyl (·CH 2 CHCO) radical.…”