TY - JOUR
T1 - Properties of diazocarbene [CNN] and the diazomethyl radical [HCNN] via ion chemistry and spectroscopy
AU - Clifford, Eileen P.
AU - Wenthold, Paul G.
AU - Lineberger, W. Carl
AU - Petersson, George A.
AU - Broadus, Katherine M.
AU - Kass, Steven R.
AU - Kato, Shuji
AU - DePuy, Charles H.
AU - Bierbaum, Veronica M.
AU - Ellison, G. Barney
PY - 1998/9/3
Y1 - 1998/9/3
N2 - We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and the diazomethyl radical: EA(X̃ 3∑- CNN) = 1.771 ± 0.010 eV, EA(X̃ 2A″ HCNN) = 1.685 ± 0.006 eV, and EA(X̃ 2A″ DCNN) = 1.678 ± 0.006 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: EA(X̃ 3∑- CNN) = 1.83 ± 0.03 eV, EA(X̃ 2A″ HCNN) = 1.69 ± 0.03 eV. We make use of the electron affinities of CNN and HCNN, together with the gas phase acidity of diazomethane, ΔacidH298(HCHN2) = 372.2 ± 2.1 kcal mol-1 (CBS calculated value = 373.4 ± 0.7), to find the bond enthalpies of H2CNN. We find DH298(H-CHN2) equal to 97 ± 2 kcal mol-1, which closely agrees with the CBS-QCI/APNO-calculated value [DH298(H-CHN2) = 98.5 ± 0.7 kcal mol-1]. From proton transfer experiments in a Fourier transform mass spectrometer and a tandem flowing afterglow-selected ion flow tube (FA-SIFT), we find ΔacidH298(HCNN) = 352 ± 4 kcal mol-1 in agreement with the CBS-QCI/ APNO-calculated value of 351.8 ± 0.7 kcal mol-1. Use of the experimental electron affinity, EA(CNN), leads to the CH bond enthalpy of the cyanoamino radical, DH298(H-CNN) = 79 ± 4 kcal mol-1 which is in excellent agreement with the CBS-QCI/APNO-calculated value: DH298(H-CNN) = 78.7 ± 0.7 kcal mol-1. If we adopt the CBS-QCI/APNO value for ΔfH298(CH2N2) [64.1 ± 0.7 kcal mol-1] as our reference, we obtain ΔfH298(HCN2) = 110 ± 2 kcal mol-1 and ΔfH298(CN2) = 136 ± 5 kcal mol-1, which are again in agreement with the CBS-QCI/APNO values: ΔfH298(HCN2) = 110.5 ± 0.7 kcal mol-1 and ΔfH298(CN2) = 138.4 ± 0.7 kcal mol-1. We recommend revised experimental values for ΔfH0(HCN) = 30.9 ± 0.7 kcal mol-1 and ΔfH298(HCN) = 30.8 ± 0.7 kcal mol-1 and find that the reaction CH (2Π) + N2 → HCN + N (4S) to be slightly endothermic, ΔrxnH0 = 1.6 ± 0.7 kcal mol-1.
AB - We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and the diazomethyl radical: EA(X̃ 3∑- CNN) = 1.771 ± 0.010 eV, EA(X̃ 2A″ HCNN) = 1.685 ± 0.006 eV, and EA(X̃ 2A″ DCNN) = 1.678 ± 0.006 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: EA(X̃ 3∑- CNN) = 1.83 ± 0.03 eV, EA(X̃ 2A″ HCNN) = 1.69 ± 0.03 eV. We make use of the electron affinities of CNN and HCNN, together with the gas phase acidity of diazomethane, ΔacidH298(HCHN2) = 372.2 ± 2.1 kcal mol-1 (CBS calculated value = 373.4 ± 0.7), to find the bond enthalpies of H2CNN. We find DH298(H-CHN2) equal to 97 ± 2 kcal mol-1, which closely agrees with the CBS-QCI/APNO-calculated value [DH298(H-CHN2) = 98.5 ± 0.7 kcal mol-1]. From proton transfer experiments in a Fourier transform mass spectrometer and a tandem flowing afterglow-selected ion flow tube (FA-SIFT), we find ΔacidH298(HCNN) = 352 ± 4 kcal mol-1 in agreement with the CBS-QCI/ APNO-calculated value of 351.8 ± 0.7 kcal mol-1. Use of the experimental electron affinity, EA(CNN), leads to the CH bond enthalpy of the cyanoamino radical, DH298(H-CNN) = 79 ± 4 kcal mol-1 which is in excellent agreement with the CBS-QCI/APNO-calculated value: DH298(H-CNN) = 78.7 ± 0.7 kcal mol-1. If we adopt the CBS-QCI/APNO value for ΔfH298(CH2N2) [64.1 ± 0.7 kcal mol-1] as our reference, we obtain ΔfH298(HCN2) = 110 ± 2 kcal mol-1 and ΔfH298(CN2) = 136 ± 5 kcal mol-1, which are again in agreement with the CBS-QCI/APNO values: ΔfH298(HCN2) = 110.5 ± 0.7 kcal mol-1 and ΔfH298(CN2) = 138.4 ± 0.7 kcal mol-1. We recommend revised experimental values for ΔfH0(HCN) = 30.9 ± 0.7 kcal mol-1 and ΔfH298(HCN) = 30.8 ± 0.7 kcal mol-1 and find that the reaction CH (2Π) + N2 → HCN + N (4S) to be slightly endothermic, ΔrxnH0 = 1.6 ± 0.7 kcal mol-1.
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U2 - 10.1021/jp9802735
DO - 10.1021/jp9802735
M3 - Article
AN - SCOPUS:11644262462
SN - 1089-5639
VL - 102
SP - 7100
EP - 7112
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 36
ER -