Browsing by Author "Amicangelo, Jay C."

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Infrared spectra of the 1,1-dimethylallyl and 1,2-dimethylallyl radicals isolated in solid para-hydrogen
(2018-11-28)
Amicangelo, Jay C.
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Lee, Yuan-Pern
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交大名義發表
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應用化學系
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應用化學系分子科學碩博班
The reaction of hydrogen atoms (H) with isoprene (C5H8) in solid para-hydrogen (p-H2) matrices at 3.2 K has been studied using infrared (IR) spectroscopy. Mixtures of C5H8 and Cl-2 were co-deposited in p-H2 at 3.2 K, followed by irradiation with ultraviolet light at 365 nm to produce Cl atoms from the Cl-2, and subsequent irradiation with IR light to produce H atoms from the reaction of the Cl atoms with p-H-2. The H atoms then react with the C5H8 to form H atom addition radicals (C5H9 center dot). Upon 365-nm/IR photolysis, a multitude of new lines appeared in the IR spectrum and, based on the secondary photolysis behavior, it was determined that the majority of the new lines belong to two distinct chemical species, denoted as setX(an intense line at 776.0 cm 1 and 12 other weaker lines) and set Y (an intense line at 766.7 cm(-1) and 12 other weaker lines). Quantum-chemical calculations were performed at the B3PW91/6-311++ G(2d, 2p) level to determine the relative energetics and predict the IR spectra for the four possible isomers of C5H9 center dot that can be produced from the addition of the H atom to the four distinct carbon atoms in C5H8. The newly observed lines of set X and Y are assigned to the 1,2-dimethylallyl (addition to carbon 4) and the 1,1-dimethylallyl (addition to carbon 1) radicals according to comparison with the predicted IR spectra of the possible products. The 1,2-dimethylallyl radical and the 1,1-dimethylallyl radical were predicted to be the most stable isomers, with the latter similar to 8 kJ mol(-1) lower in energy than the former and to have significantly lower barriers than the addition pathways for the two central carbons. The ratio of the 1,1-dimethylallyl to the 1,2-dimethylallyl radicals is estimated to be (1.0 +/- 0.5): 1.0, indicating that the two radicals are produced in similar amounts, which is consistent with the theoretical predictions that the barrier heights are very similar for the H atom addition to the two terminal carbon atoms. Published by AIP Publishing.
Infrared Spectra of the 1-Chloromethyl-1-methylallyl and 1-Chloromethyl-2-methylallyl Radicals Isolated in Solid para-Hydrogen
(2017-11-23)
Amicangelo, Jay C.
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
The reaction of chlorine atoms (Cl) with isoprene (2-methyl-1,3-butadiene, C5H8) in solid para-hydrogen (p-H-2) matrices at 3.2 K was studied using infrared (IR) spectroscopy. Mixtures of C5H8 and Cl-2 were codeposited in p-H-2 at 3.2 K, followed by irradiation with ultraviolet light at 36S nm to induce the photodissociation of Cl-2 and the subsequent reaction of the Cl atoms with C5H8. Upon 365 nm photolysis, a multitude of new lines appeared in the IR spectrum, and, based on the secondary photolysis behavior, it was determined that the majority of the new lines belong to two distinct chemical species, designated as set A (intense lines at 1237.9, 807.8, and 605.6/608.2 cm(-1), and several other weaker lines) and set B (intense lines at 942.4, 1257.7, 796.7/798.5, 667.9, and 569.7 cm(-1), and several other weaker lines). Quantum-chemical calculations were performed at the B3PW91/6-311++G(2d,2p) level for center dot C5H7 and the four possible isomers of the center dot C5H8Cl radicals, produced from the addition of the Cl atom to the four distinct sites of carbon atoms in C5H8, to determine the relative energetics and predict IR spectra for each radical. The newly observed lines of sets A and B are assigned to the 1-chloromethyl-2-methylallyl radical (addition to carbon 4) and the 1-chloromethyl-1-methylallyl radical (addition to carbon 1) according to comparison with predicted IR spectra of possible products. The 1-chloromethyl-2-methylallyl radical and 1-chloromethyl-1-methylallyl radicals were predicted to be the most stable, with the latter similar to 8 kJ mol(-1) lower in energy than the former. The ratio of the 1-chloromethyl-1-methylallyl to the 1-chloromethyl-2-methylallyl radicals is estimated to be (1.2 +/- 0.5):1.0, indicating that the two radicals are produced in approximately equal amounts. The exclusive production of the radicals involving the addition of the Cl atom to the two terminal carbons of isoprene is analogous to what was previously observed for the reaction of Cl atoms with trans-1,3-butadiene in solid p-H-2.
Infrared spectrum of the 2-chloroethyl radical in solid para-hydrogen
(2012)
Amicangelo, Jay C.
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Golec, Barbara
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Bahou, Mohammed
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Lee, Yuan-Pern
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應用化學系
The addition reaction of chlorine with ethylene (C(2)H(4)) is expected to proceed via a free radical intermediate, the 2-chloroethyl radical, however, this intermediate has not been previously observed spectroscopically. Irradiation at 365 nm of a co-deposited mixture of Cl(2), C(2)H(4), and p-H(2) at 3.2 K produces a series of new lines in the infrared spectrum. A strong line at 664.0 cm(-1) and weaker lines at 562.1, 1069.9, 1228.0, 3041.1 and 3129.3 cm(-1) are concluded to be due to a single carrier based on their behavior upon subsequent annealing to 4.5 K and secondary irradiation at 254 and 214 nm. The positions and intensities of these lines agree with the MP2/aug-cc-pVDZ predicted vibrational spectrum of the 2-chloroethyl ((center dot)CH(2)CH(2)Cl) radical. In order to confirm this assignment, isotopic experiments were performed with C(2)D(4) and t-C(2)H(2)D(2) and the corresponding infrared bands due to the deuterium isotopomers of this radical ((center dot)CD(2)CD(2)Cl and (center dot)C(2)H(2)D(2)Cl) have been observed. A final set of experiments were performed following irradiation of the Cl(2)/C(2)H(4)/p-H(2) mixture at 365 nm, in which the matrix was irradiated with filtered infrared light from a globar source, which has been shown to induce reactions between isolated Cl atoms and matrix H(2) to produce HCl and H atoms. In these experiments, the major products observed were HCl, the ethyl radical (center dot C(2)H(5)) and ethyl chloride (C(2)H(5)Cl) and the possible mechanisms for the formation of these species are discussed.
Site-Selective Reaction of Cl plus Propene in Solid para-Hydrogen: Formation of 2-Chloropropyl Radicals
(2010-10-07)
Amicangelo, Jay C.
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
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 Cl(2) 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.