Reactions between chlorine atom and acetylene in solid para-hydrogen: Infrared spectrum of the 1-chloroethyl radical

Abstract

We applied infrared matrix isolation spectroscopy to investigate the reactions between Cl atom and acetylene (C₂H₂) in a para-hydrogen (p-H₂) matrix at 3.2 K; Cl was produced via photodissociation at 365 nm of matrix-isolated Cl₂ in situ. The 1-chloroethyl radical (·CHClCH₃) and chloroethene (C₂H₃Cl) are identified as the main products of the reaction Cl + C₂H₂ in solid p-H₂. IR absorption lines at 738.2, 1027.6, 1283.4, 1377.1, 1426.6, 1442.6, and 2861.2 cm⁻¹ are assigned to the 1-chloroethyl radical. For the reaction of Cl + C₂D₂, lines due to the ·CDClCH₂D radical and trans-CHDCDCl are observed; the former likely has a syn-conformation. These assignments are based on comparison of observed vibrational wavenumbers and ¹³C- and D-isotopic shifts with those predicted with the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ methods. Our observation indicates that the primary addition product of Cl + C₂H₂, 2-chlorovinyl (·CHCHCl) reacts readily with a neighboring p-H2 molecule to form ·CHClCH₃ and C₂H₃Cl. Observation of ·CDClCH₂D and trans-CHDCDCl from Cl + C₂D₂ further supports this conclusion. Although the reactivity of p-H₂ appears to be a disadvantage for making highly reactive free radicals in solid p-H₂, the formation of 1-chloroethyl radical indicates that this secondary reaction might be advantageous in producing radicals that are difficult to prepare from simple photolysis or bimolecular reactions in situ.

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

“…3. Upon secondary photolysis at 248 nm We observed also weak absorption lines of stable products C 2 H 3 Cl at 1609.5, 943.2, and 896.5 cm −1 (group D), 46 CH 2 ClCHCO at 2141.4, 1265.4, and 1019.1 cm −1 (group E), 14 C 2 H 2 -HCl at 3274.2 and 2784.3 cm −1 (group A 1 ), 46 and C 2 H 4 -HCl at 2772.7 cm −1 (group B 1 ), 27,46 as indicated in Fig. 2 and listed in Table III.…”

“…The intensities of lines at 3294.9, 3279.6, and 733.7 cm −1 (group A, assigned to C 2 H 2 ) 46 attained maxima after photolysis at 193 nm for 15 min, but remained nearly unchanged when the matrix was subsequently irradiated with light at 248 nm. The intensity of features of C 2 H 4 (group B) 46 Table II.…”

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

“…trans- 60 To promote the reaction of C atoms with p-H 2 matrix, we removed the 2.4-μm filter and increased the aperture to 10 mm to utilize more light from the IR source of the FTIR spectrometer to excite the UV-irradiated matrix. Figure 4(d) shows the difference spectrum after irradiation of the UV-irradiated matrix with IR light for 1 h. In addition to the much enhanced line of HC at 2894.1 cm −1 and several weak ones of (HC ) n complexes in the region 2750−2900 cm −1 , several new lines appeared; they are distinct from those observed in group A shown in Fig.…”

Reactions between atomic chlorine and pyridine in solid para-hydrogen: Infrared spectrum of the 1-chloropyridinyl (C5H5N−Cl) radical

“…Taking advantage of the diminished matrix cage effect of p-H 2 , Raston and Anderson produced isolated Cl atoms by photodissociation at 355 nm of Cl 2 trapped in solid p-H 2 . 19 We have employed this method to investigate reactions of Cl with molecules including CS 2 , C 2 H 2 , C 2 H 4 , C 3 H 6 , trans-1,3-butadiene, and C 6 H 6 in p-H 2 to identify radicals ClSCS, 20 1-chloroethyl (·CHClCH 3 ), 21 2-chloropropyl (·CH 2 CHClCH 3 ), 22 2-chloroethyl (·CH 2 CH 2 Cl), 23 and trans-1-chloromethylallyl [·(CH 2 CHCH)CH 2 Cl] 24 that were difficult to produce in typical experiments either in the gaseous phase or in noble-gas matrices.…”