WordNet

use a shift key on a keyboard; "She could not shift so all her letters are written in lower case"
the time period during which you are at work (同)work shift, duty period
the act of moving from one place to another; "his constant shifting disrupted the class" (同)shifting
an event in which something is displaced without rotation (同)displacement
a crew of workers who work for a specific period of time
change place or direction; "Shift ones position" (同)dislodge, reposition
change gears; "you have to shift when you go down a steep hill"
change in quality; "His tone shifted"
change phonetically as part of a systematic historical change; "Grimm showed how the consonants shifted"
move and exchange for another; "shift the date for our class reunion"
move from one setting or context to another; "shift the emphasis"; "shift ones attention"
of or made from or using substances produced by or used in reactions involving atomic or molecular changes; "chemical fertilizer"
material produced by or used in a reaction involving changes in atoms or molecules (同)chemical substance
relating to or used in chemistry; "chemical engineer"; "chemical balance" (同)chemic
continuously varying; "taffeta with shifting colors"
changing position or direction; "he drifted into the shifting crowd"; "their nervous shifting glances"; "shifty winds" (同)shifty
(of soil) unstable; "shifting sands"; "unfirm earth" (同)unfirm

PrepTutorEJDIC

〈人・場所・位置など〉‘を'『移し替える』,置き換える / …‘を'変える,取り替える / 〈自動車のギヤ〉‘を'入れ変える / (…へ)『変わる』,移る《+『to』+『名』》 / 車のギヤを変える;〈車が〉ギヤが入れ変わる・『変換』,転換;移動 / (仕事、作業の)『交替』,交替製;交替の組(人);交替時間 / (特に,自動車)変速装置 / やりくり[算段],一時しのぎの手段,便法;ずるい手段,策略 / シフトドレス(肩から腰までまっすぐした線のゆったりしたワンピース);スリップ
『化学の』,化学上の;化学的な,化学作用による / 化学薬品の,化学薬品を用いる / 『化学薬品』(『製品』)

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/04/12 06:19:48」(JST)

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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.^[1]^[2]^[3] 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 of a magnet is calculated from the Larmor equation^[4]

where is the actual strength of the magnet in units like teslas or gauss, and is the gyromagnetic ratio of the nucleus being tested which is in turn calculated from its magnetic moment and spin number with the nuclear magneton and the Planck constant h:

Thus, the proton operating frequency for a 1 T magnet is calculated as:

\omega _0 = \gamma B_0 = \frac{{2.79 \times 5.05 \times 10^{ - 27}\,{\rm{J/T}} }}{{6.62 \times 10^{ - 34}\,{\rm{Js}} \times \left( {1/2} \right)}} \times 1\,{\rm{T}} = 42.5\,{\rm{MHz}} \,

Chemical shift referencing

Chemical shift δ is usually expressed in parts per million (ppm) by frequency, because it is calculated from

^[5]

where is the absolute resonance frequency of the sample and is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field (). Since the numerator is usually expressed in hertz, and the denominator in megahertz, delta is expressed in ppm.

The detected frequencies (in Hz) for ¹H, ¹³C, and ²⁹Si nuclei are usually referenced against TMS (tetramethylsilane) or DSS, which by the definition above have a chemical shift of zero if chosen as the reference. Other standard materials are used for setting the chemical shift for other nuclei.

Thus, an NMR signal observed at a frequency 300 Hz higher than the signal from TMS, where the TMS resonance frequency is 300 MHz, has a chemical shift of:

Although the absolute resonance frequency depends on the applied magnetic field, the chemical shift is independent of external magnetic field strength. On the other hand, the resolution of NMR will increase with applied magnetic field.

The induced magnetic field

The electrons around a nucleus will circulate in a magnetic field and create a secondary induced magnetic field. This field opposes the applied field as stipulated by Lenz's law and atoms with higher induced fields (i.e., higher electron density) are therefore called shielded, relative to those with lower electron density. The chemical milieu of an atom can influence its electron density through the polar effect. Electron-donating alkyl groups, for example, lead to increased shielding while electron-withdrawing substituents such as nitro groups lead to deshielding of the nucleus. Not only substituents cause local induced fields. Bonding electrons can also lead to shielding and deshielding effects. A striking example of this are the pi bonds in benzene. Circular current through the hyperconjugated system causes a shielding effect at the molecule's center and a deshielding effect at its edges. Trends in chemical shift are explained based on the degree of shielding or deshielding.

Nuclei are found to resonate in a wide range to the left (or more rare to the right) of the internal standard. When a signal is found with a higher chemical shift:

the applied effective magnetic field is lower, if the resonance frequency is fixed, (as in old traditional CW spectrometers)
the frequency is higher, when the applied magnetic field is static, (normal case in FT spectrometers)
the nucleus is more deshielded
the signal or shift is downfield or at low field or paramagnetic

Conversely a lower chemical shift is called a diamagnetic shift, and is upfield and more shielded.

Diamagnetic shielding

In real molecules protons are surrounded by a cloud of charge due to adjacent bonds and atoms. In an applied magnetic field (B₀) electrons circulate and produce an induced field (B_i) which opposes the applied field. The effective field at the nucleus will be B = B₀ − B_i. The nucleus is said to be experiencing a diamagnetic shielding.

Factors causing chemical shifts

Important factors influencing chemical shift are electron density, electronegativity of neighboring groups and anisotropic induced magnetic field effects.

Electron density shields a nucleus from the external field. For example, in proton NMR the electron-poor tropylium ion has its protons downfield at 9.17 ppm, those of the electron-rich cyclooctatetraenyl anion move upfield to 6.75 ppm and its dianion even more upfield to 5.56 ppm.

A nucleus in the vicinity of an electronegative atom experiences reduced electron density and the nucleus is therefore deshielded. In proton NMR of methyl halides (CH₃X) the chemical shift of the methyl protons increase in the order I < Br < Cl < F from 2.16 ppm to 4.26 ppm reflecting this trend. In carbon NMR the chemical shift of the carbon nuclei increase in the same order from around –10 ppm to 70 ppm. Also when the electronegative atom is removed further away the effect diminishes until it can be observed no longer.

Anisotropic induced magnetic field effects are the result of a local induced magnetic field experienced by a nucleus resulting from circulating electrons that can either be paramagnetic when it is parallel to the applied field or diamagnetic when it is opposed to it. It is observed in alkenes where the double bond is oriented perpendicular to the external field with pi electrons likewise circulating at right angles. The induced magnetic field lines are parallel to the external field at the location of the alkene protons which therefore shift downfield to a 4.5 ppm to 7.5 ppm range. The three-dimensional space where a diamagnetic shift is called the shielding zone with a cone-like shape aligned with the external field.

The protons in aromatic compounds are shifted downfield even further with a signal for benzene at 7.73 ppm as a consequence of a diamagnetic ring current.

Alkyne protons by contrast resonate at high field in a 2–3 ppm range. For alkynes the most effective orientation is the external field in parallel with electrons circulation around the triple bond. In this way the acetylenic protons are located in the cone-shaped shielding zone hence the upfield shift.

Magnetic properties of most common nuclei

¹H and ¹³C aren't the only nuclei susceptible to NMR experiments. A number of different nuclei can also be detected, although the use of such techniques is generally rare due to small relative sensitivities in NMR experiments (compared to ¹H) of the nuclei in question, the other factor for rare use being their slender representation in nature/organic compounds.

Magnetic properties of common nuclei^[6]
Isotope	Occurrence in nature (%)	Spin number I	Magnetic moment μ^[7]	Electric quadrupole moment (e×10⁻²⁴ cm²)	Operating frequency at 7 T (MHz)	Relative sensitivity
¹H	99.984	1/2	2.79628		300.13	1
²H	0.016	1	0.85739	2.8 x 10⁻³	46.07	0.0964
¹⁰B	18.8	3	1.8005	7.4 x 10⁻²	32.25	0.0199
¹¹B	81.2	3/2	2.6880	2.6 x 10⁻²	96.29	0.165
¹²C	98.9	0
¹³C	1.1	1/2	0.70220		75.47	0.0159
¹⁴N	99.64	1	0.40358	7.1 x 10⁻²	21.68	0.00101
¹⁵N	0.37	1/2	−0.28304		30.41	0.00104
¹⁶O	99.76	0
¹⁷O	0.0317	5/2	−1.8930	−4.0 x 10⁻³	40.69	0.0291
¹⁹F	100	1/2	2.6273		282.40	0.834
²⁸Si	92.28	0
²⁹Si	4.70	1/2	−0.5548		59.63	0.0785
³¹P	100	1/2	1.1205		121.49	0.0664
³⁵Cl	75.4	3/2	0.92091	−7.9 x 10⁻²	29.41	0.0047
³⁷Cl	24.6	3/2	0.68330	−6.2 x 10⁻²	24.48	0.0027

¹H, ¹³C, ¹⁵N, ¹⁹F and ³¹P are the five nuclei that have the greatest importance in NMR experiments:

¹H because of high sensitivity and vast occurrence in organic compounds
¹³C because of being the key component of all organic compounds despite occurring at a low abundance (1.1%) compared to the major isotope of carbon ¹²C, which has a spin of 0 and therefore is NMR inactive.
¹⁵N because of being a key component of important biomolecules such as proteins and DNA
¹⁹F because of high relative sensitivity
³¹P because of frequent occurrence in organic compounds and moderate relative sensitivity

Other chemical shifts

The related Knight shift (first reported in 1949) is observed with pure metals. The NMR chemical shift in its present-day meaning first appeared in journals in 1950. Chemical shifts with a different meaning appear in X-ray photoelectron spectroscopy as the shift in atomic core-level energy due to a specific chemical environment. The term is also used in Mössbauer spectroscopy, where similarly to NMR it refers to a shift in peak position due to the local chemical bonding environment. As is the case for NMR the chemical shift reflects the electron density at the atomic nucleus.^[8]

References

^ 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 Shift | NMRCentral
^ R.K. Harris, E.D. Becker, S.M. Cabral de Menezes, R. Goodfellow, P. Granger, Pure Appl. Chem., 2001, 73, pp. 1795-1818. DOI: 10.1351/pac200173111795
^ CRC Handbook of Chemistry and Physics 65Th Ed
^ (units of the nuclear magneton)
^ A Short History of Three Chemical Shifts Shin-ichi Nagaoka Vol. 84 No. 5 May 2007 Journal of Chemical Education 801, doi:10.1021/ed084p801

External links

www.chem.wisc.edu
BioMagResBank
wwwchem.csustan.edu^{[dead link]}
Proton chemical shifts
Carbon chemical shifts
Online tutorials (these generally involve combined use of IR, ¹H NMR, ¹³C NMR and mass spectrometry)
- Problem set 1, advanced (see also this link for more background information on spin-spin coupling)
- Problem set 2, moderate
- Problem set 4, moderate, German language (don't let that scare you away!)
- Problem set 5, the best!
- Combined solutions to problem set 5 (Problems 1–32) and (Problems 33–64)

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English Journal

Exploring the structure-activity relations of N-carbethoxyphthalimide by combining FTIR, FT-Raman and NMR spectroscopy with DFT electronic structure method.

Arjunan V1, Thillai Govindaraja S2, Ravindran P3, Mohan S4.Author information 1Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605 008, India. Electronic address: varjunftir@yahoo.com.2Research and Development Centre, Bharathiar University, Coimbatore 641 046, India.3Department of Chemistry, Mahatma Gandhi Govt. Arts College, Mahe 673 310, India.4School of Sciences and Humanities, Vel Tech University, Avadi, Chennai 600 062, India.AbstractThe complete vibrational assignment and analysis of N-carbethoxyphthalimide were carried out using the experimental FTIR and FT-Raman data in the range 4000-450 and 4000-100cm(-1), respectively along with quantum chemical studies of the compound using DFT-B3LYP gradient calculations employing the 6-31G(**), 6-311++G(**) and cc-pVDZ basis sets. The (1)H (400MHz; CDCl3) and (13)C (100MHz;CDCl3) nuclear magnetic resonance (NMR) spectra were also recorded. Due to the partial ionic nature of the carbonyl group, the carbon atoms C1 and C3 in NCEP show downfield effect and the corresponding observed chemical shift of both are observed at 163.76ppm and the carbon atom C16 in the carbethoxy group also give signal in the downfield at 148.45ppm. The active sites are determined by molecular electrostatic potential. The possible electronic transitions are determined by HOMO and LUMO orbital shapes and their energies. The structure-chemical reactivity relations of the compound were determined through chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods.
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PMID 24211807

Two new metastable forms of 6-chloroquinolin-2(1H)-one: Crystal structure, Hirshfeld surfaces and spectroscopic studies.

Luo YH1, Sun BW2.Author information 1College of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China.2College of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China. Electronic address: chmsunbw@seu.edu.cn.AbstractTwo new metastable crystalline forms of 6-chloroquinolin-2(1H)-one (forms II and III), which were induced by two kinds of 3D inorganic anions (ClO4(-) and BF4(-)), have been prepared and characterized in this work. We performed single-crystal diffraction, X-ray powder diffraction (XRPD), Hirshfeld surfaces, solid-state vibrational spectroscopy (IR) and thermal analysis (DSC, TGA) to these two new forms as well as the original one (form I). Form I featured with 1D chain, while form II and III featured with dimeric unit with stronger π⋯π and hydrogen bonds interactions. The 3D inorganic anions force the self-assemble behavior of 6-chloroquinolin-2(1H)-one molecules from 1D chain structure (form I) to dimeric unit (forms II and III) due to their large steric hindrance, and different anions induced different orientations for dimeric unit. These transformations lead to the increase of N-H⋯O, π⋯π, and Cl-Cl intermolecular interactions, which lead to blue shift of IR spectra in 1700-1500cm(-1) region as well as luminescence peaks, while red shift of IR spectra in 650-550cm(-1) region.
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Two new metastable crystalline forms of 6-chloroquinolin-2(1H)-one (forms II and III), which were induced by two kinds of 3D inorganic anions (ClO4(-) and BF4(-)), have been prepared and characterized in this work. We performed single-crystal diffraction, X-ray powder diffraction (XRPD), Hirshfeld s
PMID 24211619

The synthesis, characterization and theoretical study on nicotinic acid [1-(2,3-dihydroxyphenyl)methylidene]hydrazide.

Dege N1, Senyüz N2, Batı H2, Günay N3, Avcı D4, Tamer O3, Atalay Y3.Author information 1Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Physics, 55139 Samsun, Turkey.2Ondokuz Mayıs University, Faculty of Arts and Sciences, Department of Chemistry, 55139 Samsun, Turkey.3Sakarya University, Faculty of Arts and Sciences, Department of Physics, 54140 Sakarya, Turkey.4Sakarya University, Faculty of Arts and Sciences, Department of Physics, 54140 Sakarya, Turkey. Electronic address: davci@sakarya.edu.tr.AbstractIn this study, we reported a combined experimental and theoretical study on nicotinic acid [1-(2,3-dihydroxyphenyl)methylidene]hydrazide (C13H11N3O3) molecule. The title compound was prepared and characterized by (1)H and (13)C FT-NMR, FT-IR and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P21/c with a=6.2681(3)Å, b=16.5309(7)Å, c=12.4197(6)Å, α=90°, β=111.603(4)°, γ=90° and Z=4. In addition, the molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO), continuous set of gauge transformations (CSGT), individual gauges for atoms in molecules (IGAIM) (1)H and (13)C NMR chemical shift values, natural bond orbital (NBO), nonlinear optical (NLO) and HOMO-LUMO analyses, molecular electrostatic potentials (MEPs) and thermodynamic properties of the title compound in the ground state were investigated by using Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with 6-311++G(d,p). Besides, the hardness and electronegativity parameters were obtained from HOMO and LUMO energies. Obtained results indicate that there is a good agreement between the experimental and theoretical data.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.Spectrochim Acta A Mol Biomol Spectrosc.2014 Feb 24;120:323-31. doi: 10.1016/j.saa.2013.10.030. Epub 2013 Oct 17.
In this study, we reported a combined experimental and theoretical study on nicotinic acid [1-(2,3-dihydroxyphenyl)methylidene]hydrazide (C13H11N3O3) molecule. The title compound was prepared and characterized by (1)H and (13)C FT-NMR, FT-IR and single-crystal X-ray diffraction. The compound crystal
PMID 24184926

Japanese Journal

Strain-induced nanostructure of Pb(Mg

Jpn. J. Appl. Phys. 56(10S), 10PB12, 2017-09-28
NAID 150000114786

Factors Influencing Variations in the Density, Extent of Canopy Cover, and Origin of Trees in Paddy Fields in a Rainfed Rice-Farming Village in Northeast Thailand

Southeast Asian Studies 6(2), 307-324, 2017-08
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Current-driven magnetic domain wall motion and its real-time detection

Jpn. J. Appl. Phys. 56(8), 0802A4, 2017-06-19
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リンク元	「化学シフト」
拡張検索	「chemical shift artifact」「chemical shift imaging」
関連記事	「shift」「chemical」「chemicals」