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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Revised Structure for the Diphenylaminyl Radical: The Importance of Theory in the Assignment of Electronic Transitions in Ph_2X~·(X = CH, N) and PhY~· (Y = CH_2, NH, O)
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Revised Structure for the Diphenylaminyl Radical: The Importance of Theory in the Assignment of Electronic Transitions in Ph_2X~·(X = CH, N) and PhY~· (Y = CH_2, NH, O)

机译：修订的二苯胺基自由基结构：在Ph_2X〜·（X = CH，N）和PhY〜·（Y = CH_2，NH，O）中电子跃迁的分配中理论的重要性

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Density functional theory indicates that the minimum energy structure of the diphenylaminyl radical, PH_2N·, has a "staggered" conformation in which the two phenyl rings are twisted relative to each other by an angle, φ, of 40°. In this conformation, the aromatic rings are oriented so as to maximize interaction with the unpaired electron while minimizing repulsion between the 2- and 2'-hydrogen atoms. This calculated ground state structure of Ph_2N· differs from that, which has been accepted for the past 15 years, which had the two rings orthogonal (φ = 90°) with one ring conjugating with the nitrogen's lone pair and the other conjugating with the unpaired electron. This structure was based on unexpected differences between the UV-Vis absorption spectra of Ph_2N~· and the diphenylmethyl radical. However, our calculations indicate that this orthogonal structure lies 3.5 kcal/mol above the global minimum. Further support for the staggered conformation of Ph_2N~· is provided by the similarities between absorption transition wavelengths determined theoretically and the experimental absorption bands of Ph_2N~· and other diarylaminyl radicals generated by laser flash photolysis. The long wavelength transition of Ph_2N~·, resulting in a structure that can be represented as (Ph_2)~+N~-, is red-shifted as compared to the related transition from Ph_2CH~· to (Ph_2)~+CH~- due to the electronegativity of the N atom. The absorption bands for PhCH_2~·, PHNH~·, and PhO~· in the 300-450 nm region are similar in position, which has been taken to indicate that for isoelectronic species the electronic transition energies should be little affected by heteroatom substitution. Our calculations show, however, that these sets of absorption bands arise from different transitions. Therefore, the experimentally similar 300-450 nm absorption bands for these three radicals are fortuitous and do not reflect some common, unifying traits, a fact that further serves to emphasize the importance of theory in the assignment of bands due to electronic transitions.
机译：密度泛函理论表明，二苯胺基自由基的最小能量结构PH_2N·具有“交错”构型，其中两个苯环相对于彼此扭转了40°的角。在该构象中，芳环的取向使得与未成对电子的相互作用最大化，同时使2-和2'-氢原子之间的排斥最小。该计算的Ph_2N·基态结构不同于过去15年所接受的基态结构，它具有两个正交的环（φ= 90°），其中一个环与氮的孤对共轭，另一个环与非对偶合。电子。该结构是基于Ph_2N〜·的UV-Vis吸收光谱与二苯甲基自由基之间的意外差异所致。但是，我们的计算表明该正交结构比全局最小值高3.5 kcal / mol。理论上确定的吸收跃迁波长与由激光闪光光解法产生的Ph_2N〜·和其他二芳基自由基的实验吸收带之间的相似性为Ph_2N〜·的交错构象提供了进一步的支持。与从Ph_2CH〜·到（Ph_2）〜+ CH〜-的相关跃迁相比，Ph_2N〜·的长波长跃迁导致可表示为（Ph_2）〜+ N〜-的结构发生了红移。由于N原子的电负性。在300-450 nm范围内，PhCH_2〜·，PHNH〜·和PhO〜·的吸收带在位置上相似，这表明对等电子物种，电子跃迁能几乎不受杂原子取代的影响。然而，我们的计算表明，这些吸收带集来自不同的跃迁。因此，这三个自由基在实验上相似的300-450 nm吸收带是偶然的，不能反映某些共同的统一特性，这一事实进一步有助于强调由于电子跃迁，理论在带分配中的重要性。

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