Substituted effects on bonding characteristics of cyclopentane-1,3-diyl diradicals monitored by time-resolved infrared spectroscopy

IF 1.9 4区 化学 Q2 CHEMISTRY, ORGANIC
Masato Kondoh, Shunsuke Kuboki, Hidetaka Kume, Eriku Oda, Manabu Abe, Taka-aki Ishibashi
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Abstract

Cyclopentane-1,3-diyl diradicals (DRs) provide excellent opportunities to study the properties of diradicals because their lifetimes can be significantly lengthened to up to milliseconds with the introduction of proper substituents. This study investigated the bonding characteristics of singlet and triplet DRs having C=O and p-cyanophenyl groups (S-DR3 and T-DR3) by monitoring the photo-induced formation of the diradicals from their precursor azo compounds using time-resolved IR (TR-IR) spectroscopy. Upon the formation of S-DR3, a C=O stretching wavenumber was upshifted by 22 cm−1, whereas a C≡N stretching one was downshifted by 12 cm−1. The observed shifts indicate that the unpaired electrons increase and decrease the C=O and C≡N bond orders, respectively. The effects of the unpaired electrons in S-DR3 were similar to those observed in our previous TR-IR studies on a singlet cyclopentane-1,3-diyl diradical having C=O but no C≡N groups (S-DR2) and on that having C≡N but no C=O groups (S-DR1), respectively. Contrastingly, upon the formation of T-DR3, the C=O wavenumber was downshifted by 16 cm−1, indicating that the unpaired electrons decrease the C=O bond order. More notably, no detectable shifts were observed in the C≡N stretching wavenumber. These observations are not clearly explained by a model suggested in the previous studies on S-DRs. Here, we discuss and propose a more elaborated resonance hybrid of DRs that can explain the directions and relative magnitudes of the observed wavenumber shifts irrespective of spin multiplicities. We expect that the findings and suggestions presented here will stimulate research in both organic and theoretical chemistry.

Abstract Image

Abstract Image

时间分辨红外光谱法监测环戊烷-1,3-二基二缩醛键合特性的取代效应
环戊烷-1,3-二元二环(DRs)为研究二元二环的特性提供了绝佳的机会,因为引入适当的取代基后,它们的寿命可显著延长至毫秒级。本研究通过使用时间分辨红外光谱(TR-IR)监测光诱导的二呋喃从其前体偶氮化合物中形成的过程,研究了具有 C=O 和对氰基苯基基团的单重和三重二呋喃(S-DR3 和 T-DR3)的成键特性。S-DR3 形成后,C=O 伸展波的波长上移了 22 厘米-1,而 C≡N 伸展波的波长下移了 12 厘米-1。观察到的位移表明,未配对电子分别增加和减少了 C=O 和 C≡N 键的阶数。S-DR3 中的非配对电子的影响与我们之前对具有 C=O 但不含 C≡N 基团的单环戊烷-1,3-二元醇(S-DR2)和具有 C≡N 但不含 C=O 基团的单环戊烷-1,3-二元醇(S-DR1)进行的 TR-IR 研究中观察到的影响相似。相反,在形成 T-DR3 时,C=O 波长下移了 16 厘米-1,这表明未配对的电子降低了 C=O 键的顺序。更值得注意的是,在 C≡N 伸展波中没有观察到任何移动。以往关于 S-DR 的研究中提出的模型并不能清楚地解释这些观察结果。在此,我们讨论并提出了一种更为详尽的 DR 共振混合模型,它可以解释所观察到的波长位移的方向和相对大小,而与自旋倍率无关。我们希望本文的发现和建议能促进有机化学和理论化学的研究。
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来源期刊
CiteScore
3.60
自引率
11.10%
发文量
161
审稿时长
2.3 months
期刊介绍: The Journal of Physical Organic Chemistry is the foremost international journal devoted to the relationship between molecular structure and chemical reactivity in organic systems. It publishes Research Articles, Reviews and Mini Reviews based on research striving to understand the principles governing chemical structures in relation to activity and transformation with physical and mathematical rigor, using results derived from experimental and computational methods. Physical Organic Chemistry is a central and fundamental field with multiple applications in fields such as molecular recognition, supramolecular chemistry, catalysis, photochemistry, biological and material sciences, nanotechnology and surface science.
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