A method of determining the conformation of a molecule using various physical and chemical measurements, organic chemical reactions, and analytical methods. Conformation studies often deal with molecules dynamically, and investigate the shape of the molecule that exists for an extremely short time. The compounds studied are diverse, from simple to complex, and many analytical methods are used. For example, ethane is a gas, has an extremely low melting point, and has a symmetrical molecular shape, so X-ray diffraction and dipole moment measurements cannot be used. Therefore, thermodynamic calculations of the internal energy of the molecule, Raman spectroscopy, and infrared spectroscopy were used. Dichloroethane has low symmetry due to the presence of chlorine atoms, and the bonds are polar, so dipole moments, infrared spectroscopy, and electron diffraction were effectively used to determine the conformation. The chair conformation of cyclohexane was confirmed by electron diffraction and infrared spectroscopy, and thermodynamic calculations were performed to determine the repulsive forces of the hydrogen atoms within the molecule (→ chair conformation). Nuclear magnetic resonance absorption was used to determine the motion of the hydrogen atoms. Certain cyclohexanol derivatives have hydroxyl groups bonded to the carbon ring via axial and equatorial bonds, and chemical reactions (the latter are easily esterified) were used to characterize them. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
種々の物理化学的測定法,有機化学反応,および分析法を利用して分子の立体配座を決める方法。立体配座の研究は分子を動的に扱い,きわめて短時間に存在する分子の形を追究することが多い。対象となる化合物も簡単なものから複雑なものまで多種多様であって,多くの解析法が用いられる。たとえばエタンは気体で,融点がきわめて低く,分子の形が対称であるために,X線回折や双極子能率測定を用いることができない。したがって分子の内部エネルギーについての熱力学的計算とラマンスペクトル,赤外線スペクトルが用いられた。ジクロロエタンは塩素原子が存在するために,対称性が低く,結合に極性があるので,双極子能率,赤外線スペクトル,電子線回折などが有効に使われて立体配座が決められた。イス形のシクロヘキサンは電子線回折や赤外線スペクトルによって立証され,分子内水素原子の反発力については熱力学的計算が行われた (→イス形 ) 。また水素原子の運動については核磁気共鳴吸収が用いられた。ある種のシクロヘキサノール誘導体は水酸基がアクシアル結合で炭素原子環に結合しているものと,エカトリアル結合で結合しているものとがある。この解析には化学反応 (後者は容易にエステル化される) が用いられた。
出典 ブリタニカ国際大百科事典 小項目事典ブリタニカ国際大百科事典 小項目事典について 情報 |
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