Department of Chemistry & Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
J Phys Chem A. 2010 Jan 28;114(3):1498-507. doi: 10.1021/jp907806g.
When the propargyl radical, HCCCH(2), and O(2) are codeposited onto a cold argon matrix, a chemical reaction ensues; infrared absorption spectra reveal the formation of the propargyl peroxyl radical: HC=C-CH(2) X (2)B(1) + O(2) --> trans-HC=C-CH(2)OO X (2)A. We do not observe the isomeric adduct, CH(2)=C=CHOO X (2)A''. The propargyl radicals are produced by a hyperthermal nozzle while a second nozzle alternately fires bursts of O(2)/Ar at the 20 K matrix. The absorption spectra of the radicals are measured using a Fourier transform infrared spectrometer. We observe 13 of the 18 fundamental infrared bands of the propargyl peroxyl radical in an Ar matrix at 20 K. The experimental frequencies (cm(-1)) of trans-HC[triple bond]C-CH(2)OO X (2)A'' are assigned. The a' modes are nu(1) = 3326, nu(2) = 2960, nu(3) = 2148, nu(4) = 1440, nu(5) = 1338, nu(6) = 1127, nu(7) = 982, nu(8) = 928, nu(9) = 684, and nu(10) = 499 cm(-1), while the a'' modes are nu(14) = 1218, nu(15) = 972, and nu(16) = 637 cm(-1). Linear dichroism spectra were measured with photo-oriented HCCCH(2)OO radical samples to establish the experimental polarizations of several vibrational bands. The experimental frequencies (nu) for the propargyl peroxyl radical are compared to the anharmonic frequencies (upsilon) resulting from electronic structure calculations. We have used CBS-QB3 electronic structure calculations to estimate the peroxyl bond energies: DeltaH(298)(trans-HC[triple bond]CCH(2)-OO --> CH(2)CCH X (2)B(1) + O(2)) = 19 +/- 1 kcal mol(-1) and DeltaH(298)(trans-CH(2)=C=CH-OO --> CH(2)CCH X (2)B(1) + O(2)) = 21 +/- 1 kcal mol(-1). The experimental thermochemistry for C(3)H(3) reacting with oxygen has been reanalyzed as Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)=C=O + HCO) = -83 +/- 3 kcal mol(-1); Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(3)CO + CO) = -111 +/- 3 kcal mol(-1); Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)CHO + CO) = -106 +/- 4 kcal mol(-1); Delta(rxn)H(298)(HCCCH(2) + O(2) --> HCHO + HCCO) = -67 +/- 4 kcal mol(-1); Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)CH + CO(2)) = -105 +/- 3 kcal mol(-1).
当炔丙基自由基、HCCCH(2) 和 O(2) 共沉积在冷氩基质上时，会发生化学反应；红外吸收光谱揭示了炔丙基过氧自由基的形成：HC=C-CH(2) X (2)B(1) + O(2) --> trans-HC=C-CH(2)OO X (2)A。我们没有观察到异构加合物 CH(2)=C=CHOO X (2)A''。炔丙基自由基是通过超热喷嘴产生的，而第二个喷嘴则交替向 20 K 基质发射 O(2)/Ar 脉冲。使用傅里叶变换红外光谱仪测量自由基的吸收光谱。我们在 20 K 的氩基质中观察到炔丙基过氧自由基的 18 个基本红外带中的 13 个。trans-HC[triple bond]C-CH(2)OO X (2)A'' 的实验频率（cm(-1)) 被分配。a' 模式的振动频率为 nu(1) = 3326、nu(2) = 2960、nu(3) = 2148、nu(4) = 1440、nu(5) = 1338、nu(6) = 1127、nu(7) = 982、nu(8) = 928、nu(9) = 684 和 nu(10) = 499 cm(-1)，而 a'' 模式的振动频率为 nu(14) = 1218、nu(15) = 972 和 nu(16) = 637 cm(-1)。使用光取向的 HCCCH(2)OO 自由基样品测量线性二色光谱，以确定几个振动带的实验偏振。炔丙基过氧自由基的实验频率（nu）与电子结构计算得出的非谐频率（upsilon）进行比较。我们使用 CBS-QB3 电子结构计算来估计过氧键能：DeltaH(298)(trans-HC[triple bond]CCH(2)-OO --> CH(2)CCH X (2)B(1) + O(2)) = 19 +/- 1 kcal mol(-1) 和 DeltaH(298)(trans-CH(2)=C=CH-OO --> CH(2)CCH X (2)B(1) + O(2)) = 21 +/- 1 kcal mol(-1)。重新分析了 C(3)H(3) 与氧气反应的实验热化学，得到 Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)=C=O + HCO) = -83 +/- 3 kcal mol(-1)；Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(3)CO + CO) = -111 +/- 3 kcal mol(-1)；Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)CHO + CO) = -106 +/- 4 kcal mol(-1)；Delta(rxn)H(298)(HCCCH(2) + O(2) --> HCHO + HCCO) = -67 +/- 4 kcal mol(-1)；Delta(rxn)H(298)(HCCCH(2) + O(2) --> CH(2)CH + CO(2)) = -105 +/- 3 kcal mol(-1)。
