Negative Ion Photoelectron Spectroscopy Confirms the Prediction that 1,2,4,5-Tetraoxatetramethylenebenzene Has a Singlet Ground State

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• 作者：David A. Hrovat ; Gao-Lei Hou ; Xue-Bin Wang ; Weston Thatcher Borden
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：July 22, 2015
• 年：2015
• 卷：137
• 期：28
• 页码：9094-9099
• 全文大小：359K
• ISSN：1520-5126

文摘

The negative ion photoelectron (NIPE) spectrum of 1,2,4,5-tetraoxatetramethylenebenzene radical anion (TOTMB^{鈥⑩€?/sup>) shows that, like the hydrocarbon, 1,2,4,5-tetramethylenebenzene (TMB), the TOTMB diradical has a singlet ground state and thus violates Hund鈥檚 rule. The NIPE spectrum of TOTMB鈥⑩€?/sup> gives a value of 鈭捨?i>E_ST = 3.5 卤 0.2 kcal/mol for the energy difference between the singlet and triplet states of TOTMB and a value of EA = 4.025 卤 0.010 eV for the electron affinity of TOTMB. (10/10)CASPT2 calculations are successful in predicting the singlet鈥搕riplet energy difference in TOTMB almost exactly, giving a computed value of 鈭捨?i>E_ST = 3.6 kcal/mol. The same type of calculations predict 鈭捨?i>E_ST = 6.1鈥?.3 kcal/mol in TMB. Thus, the calculated effect of the substitution of the four oxygens in TOTMB for the four methylene groups in TMB is very unusual, since the singlet state is selectively destabilized relative to the triplet state. The reason why TMB 鈫?TOTMB is predicted to result in a decrease in the size of 鈭捨?i>E_ST is discussed.}