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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Chemical shift ： ウィキペディア英語版 Chemical shift In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of a nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule.〔''Spectrometric Identification of organic Compounds'' Silverstein, Bassler, Morrill 4th Ed. ISBN 0-471-09070-0〕〔''Organic Spectroscopy'' William Kemp 3rd Ed. ISBN 0-333-41767-4〕〔''Basic 1H - 13C-NMR spectroscopy'' Metin Balei ISBN 0-444-51811-8〕 Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy. Some atomic nuclei possess a magnetic moment (nuclear spin), which gives rise to different energy levels and resonance frequencies in a magnetic field. The total magnetic field experienced by a nucleus includes local magnetic fields induced by currents of electrons in the molecular orbitals (note that electrons have a magnetic moment themselves). The electron distribution of the same type of nucleus (e.g. 1H, 13C, 15N) usually varies according to the local geometry (binding partners, bond lengths, angles between bonds, ...), and with it the local magnetic field at each nucleus. This is reflected in the spin energy levels (and resonance frequencies). The variations of nuclear magnetic resonance frequencies of the same kind of nucleus, due to variations in the electron distribution, is called the chemical shift. The size of the chemical shift is given with respect to a reference frequency or reference sample (see also ''chemical shift referencing''), usually a molecule with a barely distorted electron distribution. ==Operating frequency== The operating (or Larmor) frequency $\backslash omega\_0$ of a magnet is calculated from the Larmor equation〔(Chemical Shift | NMRCentral )〕 : $\backslash omega\_\; =\; \backslash gamma\; B\_0\backslash ,$ where $B\_0$ is the actual strength of the magnet in units like teslas or gauss, and $\backslash gamma$ is the gyromagnetic ratio of the nucleus being tested which is in turn calculated from its magnetic moment $\backslash mu$ and spin number $I$ with the nuclear magneton $\backslash mu\_N$ and the Planck constant h: : $\backslash gamma\; =\; \backslash frac\backslash ,$ Thus, the proton operating frequency for a 1 T magnet is calculated as: : $$ \omega _0 = \gamma B_0 = \frac }} \times \left( \right)}} \times 1\,} \, 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chemical shift」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.