IRとラーマン光譜によるsp-炭素鎖の溶液状態非線形性の証拠:相互排斥の違反
Andrea Lucotti1, Matteo Tommasini, Daniele Fazzi
1Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica G. Natta Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
Journal of the American Chemical Society
|February 10, 2009
まとめ
アダマンチル末端のポリエンは非中心対称な構造を示しており,これはスペクトロスコピーとX線分析によって確認されています. この分子非対称性は,末端グループとは無関係な鎖の柔軟性から生じ,それらの非線形特性に影響を与えます.
科学分野:
- 分子スペクトロスコピーは,分子スペクトロスコピーを用います.
- 有機化学 オーガニック・ケミストリー
- 固体化学 固体化学
背景:
- ポリインは,交互に単一結合と三重結合を交互に持つ炭素鎖である.
- ポリエンの構造と性質を理解することは,材料科学にとって極めて重要です.
- 非中心対称な分子は,非線形光学アプリケーションに不可欠です.
研究 の 目的:
- アダマンチル末端のポリーネスを合成し,特徴づけること.
- スペクトロスコーピーを用いてポリエンの分子構造を調査する.
- ポリイネの分子対称性を影響する要因を決定する.
主な方法:
- アダマンチル末端のポリアンの合成 (C4-C20).
- 分子振動を分析するための赤外線 (IR) とラーマン光譜法.
- C12のX線結晶分析
- 密度関数理論 (DFT) による計算.
主要な成果:
- 顕微鏡の証拠は,固体状態と溶液状態のポリアインの非中心対称構造を示しています.
- C12のX線解析は,曲げられた,非中心対称な構造を確認しています.
- DFTの計算は,この構造的特徴のエンドグループの独立性を示しています.
- IRとラーマンスペクトルの相互排斥原理の違反は,重要な構造的洞察を提供します.
結論:
- アダマンチル末端のポリエンは,非中心対称な構造を持っています.
- 分子非線形性は,低周波の屈折振動や屈折形状に起因する.
- エンドグループは,観察された分子不対称性を決定しません.
関連する概念動画
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
01:20Raman Spectroscopy: Overview
The underlying principle of Raman spectroscopy is based on the interaction between light and matter, specifically molecules' inelastic scattering of photons. When a monochromatic beam of light, typically from a laser source, interacts with a sample, most scattered light has the same frequency as the incident light. This is known as Rayleigh scattering.
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
01:24IR Spectroscopy: Molecular Vibration Overview
When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
01:21IR Absorption Frequency: Hybridization
Hydrocarbons such as alkanes, alkenes, and alkynes show characteristic C–H stretching absorption bands. These IR stretching frequencies depend on the hybridization of the involved carbon atom and can be explained in terms of the s character of each hybridized atomic orbital.
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that stretch at a...
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that stretch at a...