Chemical shift

Last updated December 05, 2023

In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic 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 (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 so on), 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 $\omega _{0}$ of a magnet (usually quoted as absolute value in MHz) is calculated from the Larmor equation ^[4]

\omega _{0}=-\gamma B_{0}\,,

where $B 0$ is the induction of the magnet (SI units of Tesla), and $\gamma$ is the magnetogyric ratio of the nucleus — an empirically measured fundamental constant determined by the details of the structure of each nucleus. For example, the proton operating frequency for a 1 Tesla magnet is calculated as:

{{\omega }_{0}}=-4.258\cdot {{10}^{7}}{\frac {\text{Hz}}{\text{T}}}\times 1.000{\text{ T}}=-42.58{\text{ MHz}}

MRI scanners are often referred to by their field strengths $B 0$ (e.g. "a 7 T scanner"), whereas NMR spectrometers are commonly referred to by the corresponding proton Larmor frequency (e.g. "a 300 MHz spectrometer", which has a $B 0$ of 7 T ). While chemical shift is referenced in order that the units are equivalent across different field strengths, the actual frequency separation in Hertz scales with field strength ( $B 0$ ). As a result, the difference of chemical shift between two signals (ppm) represents a larger number of Hertz on machines that have larger $B 0$ and therefore the signals are less likely to be overlapping in the resulting spectrum. This increased resolution is a significant advantage for analysis. (Larger field machines are also favoured on account of having intrinsically higher signal arising from the Boltzmann distribution of magnetic spin states.)

Chemical shift referencing

Chemical shift $δ$ is usually expressed in parts per million (ppm) by frequency, because it is calculated from:^[5]

\delta ={\frac {\nu _{\mathrm {sample} }-\nu _{\mathrm {ref} }}{\nu _{\mathrm {ref} }}}\,,

where $ν sample$ is the absolute resonance frequency of the sample and $ν ref$ is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field $B 0$ . Since the numerator is usually expressed in hertz, and the denominator in megahertz, $δ$ is expressed in ppm.

The detected frequencies (in Hz) for ¹H, ¹³C, and ²⁹Si nuclei are usually referenced against TMS (tetramethylsilane), TSP (Trimethylsilylpropanoic acid), 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:

{\frac {300\,{\rm {Hz}}}{300\times 10^{6}\,{\rm {Hz}}}}=1\times 10^{-6}=1\,{\rm {ppm\,.}}

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.

Referencing methods

Practically speaking, diverse methods may be used to reference chemical shifts in an NMR experiment, which can be subdivided into indirect and direct referencing methods.^[5] Indirect referencing uses a channel other than the one of interest to adjust chemical shift scale correctly, i.e. the solvent signal in the deuterium (lock) channel can be used to reference the a ¹H NMR spectrum.^[5] Both indirect and direct referencing can be done as three different procedures:

Internal referencing, where the reference compound is added directly to the system under study."^[5] In this common practice, users adjust residual solvent signals of ¹H or ¹³C NMR spectra with calibrated spectral tables.^[6]^[7] If substances other than the solvent itself are used for internal referencing, the sample has to be combined with the reference compound, which may affect the chemical shifts.
External referencing, involving sample and reference contained separately in coaxial cylindrical tubes."^[5] With this procedure, the reference signal is still visible in the spectrum of interest, although the reference and the sample are physically separated by a glass wall. Magnetic susceptibility differences between the sample and the reference phase need to be corrected theoretically,^[5] which lowers the practicality of this procedure.
Substitution method: The use of separate cylindrical tubes for the sample and the reference compound, with (in principle) spectra recorded individually for each."^[5] Similar to external referencing, this method allows referencing without sample contamination. If field/frequency locking via the ²H signal of the deuterated solvent is used and the solvents of reference and analyte are the same, the use of this methods is straightforward. Problems may arise if different solvents are used for the reference compound and the sample as (just like for external referencing) magnetic susceptibility differences need to be corrected theoretically.^[5]^[8] If this method is used without field/frequency locking, shimming procedures between the sample and the reference need to be avoided as they change the applied magnetic field (and thereby influence the chemical shift).^[5]

Modern NMR spectrometers commonly make use of the absolute scale,^[8]^[5] which defines the ¹H signal of TMS as 0 ppm in proton NMR and the center frequencies of all other nuclei as percentage of the TMS resonance frequency:^[5]^[8]

\Xi [\%]=100(\upsilon _{X}^{obs}/\upsilon _{TMS}^{obs})

The use of the deuterium (lock) channel, so the ²H signal of the deuterated solvent, and the Ξ value of the absolute scale is a form of internal referencing and is particularly useful in heteronuclear NMR spectroscopy as local reference compounds may not be always be available or easily used (i.e. liquid NH₃ for ¹⁵N NMR spectroscopy). This system, however, relies on accurately determined ²H NMR chemical shifts enlisted in the spectrometer software and correctly determined Ξ values by IUPAC.^[5]^[8] A recent study for ¹⁹F NMR spectroscopy revealed that the use of the absolute scale and lock-based internal referencing led to errors in chemical shifts.^[9]^[10] These may be negated by inclusion of calibrated reference compounds.^[9]^[10]

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. Electron-donating alkyl groups, for example, lead to increased shielding whereas 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 is 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 ( $B 0$ ) electrons circulate and produce an induced field ( $B i$ ) which opposes the applied field. The effective field at the nucleus will be $B = B 0 - B i$ . 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 are not 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 and organic compounds.

Magnetic properties of common nuclei^[11]
Isotope	Occurrence in nature (%)	Spin number $I$	Magnetic moment $μ$ ( $μ N$ )	Electric quadrupole moment ( $e$ × 10⁻²⁴ cm²)	Operating frequency at 7 T (MHz)	Relative sensitivity
¹H	099.984	1/2	−2.79628	−0	300.13	1
²H	000.016	1	−0.85739	−0.0028	046.07	0.0964
¹⁰B	018.8	3	−1.8005	−0.074	032.25	0.0199
¹¹B	081.2	3/2	−2.6880	−0.026	096.29	0.165
¹²C	098.9	0	−0	−0	000	0
¹³C	001.1	1/2	−0.70220	−0	075.47	0.0159
¹⁴N	099.64	1	−0.40358	−0.071	021.68	0.00101
¹⁵N	000.37	1/2	−0.28304	−0	030.41	0.00104
¹⁶O	099.76	0	−0	−0	000	0
¹⁷O	000.0317	5/2	−1.8930	−0.0040	040.69	0.0291
¹⁹F	100	1/2	−2.6273	−0	282.40	0.834
²⁸Si	092.28	0	−0	−0	000	0
²⁹Si	004.70	1/2	−0.5548	−0	059.63	0.0785
³¹P	100	1/2	−1.1205	−0	121.49	0.0664
³⁵Cl	075.4	3/2	−0.92091	−0.079	029.41	0.0047
³⁷Cl	024.6	3/2	−0.68330	−0.062	024.48	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

Chemical shift manipulation

In general, the associated increased signal-to-noise and resolution has driven a move towards increasingly high field strengths. In limited cases, however, lower fields are preferred; examples are for systems in chemical exchange, where the speed of the exchange relative to the NMR experiment can cause additional and confounding linewidth broadening. Similarly, while avoidance of second order coupling is generally preferred, this information can be useful for elucidation of chemical structures. Using refocussing pulses placed between recording of successive points of the free induction decay, in an analogous fashion to the spin echo technique in MRI, the chemical shift evolution can be scaled to provide apparent low-field spectra on a high-field spectrometer.^[12] In a similar fashion, it is possible to upscale the effect of J-coupling relative to the chemical shift using pulse sequences that include additional J-coupling evolution periods interspersed with conventional spin evolutions.^[13]

Other chemical shifts

The Knight shift (first reported in 1949) and Shoolery's rule are observed with pure metals and methylene groups, respectively. 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.^[14]

Related Research Articles

Dynamic nuclear polarization (DNP) results from transferring spin polarization from electrons to nuclei, thereby aligning the nuclear spins to the extent that electron spins are aligned. Note that the alignment of electron spins at a given magnetic field and temperature is described by the Boltzmann distribution under the thermal equilibrium. It is also possible that those electrons are aligned to a higher degree of order by other preparations of electron spin order such as: chemical reactions, optical pumping and spin injection. DNP is considered one of several techniques for hyperpolarization. DNP can also be induced using unpaired electrons produced by radiation damage in solids.

<span class="mw-page-title-main">Nuclear magnetic resonance spectroscopy</span> Laboratory technique

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic field. This re-orientation occurs with absorption of electromagnetic radiation in the radio frequency region from roughly 4 to 900 MHz, which depends on the isotopic nature of the nucleus and increased proportionally to the strength of the external magnetic field. Notably, the resonance frequency of each NMR-active nucleus depends on its chemical environment. As a result, NMR spectra provide information about individual functional groups present in the sample, as well about connections between nearby nuclei in the same molecule. As the NMR spectra are unique or highly characteristic to individual compounds and functional groups, NMR spectroscopy is one of the most important methods to identify molecular structures, particulary of organic compounds.

Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but the spins excited are those of the electrons instead of the atomic nuclei. EPR spectroscopy is particularly useful for studying metal complexes and organic radicals. EPR was first observed in Kazan State University by Soviet physicist Yevgeny Zavoisky in 1944, and was developed independently at the same time by Brebis Bleaney at the University of Oxford.

Carbon-13 (C13) nuclear magnetic resonance is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. ¹³C NMR detects only the ¹³
C isotope. The main carbon isotope, ¹²
C does not produce an NMR signal. Although ca. 1 mln. times less sensitive than ¹H NMR spectroscopy, ¹³C NMR spectroscopy is widely used for characterizing organic and organometallic compounds, primarily because 1H-decoupled 13C-NMR spectra are more simple, have a greater sensitivity to differences in the chemical structure, and, thus, are better suited for identifying molecules in complex mixtures. At the same time, such spectra lack quantitative information about the atomic ratios of different types of carbon nuclei, because nuclear Overhauser effect used in 1H-decoupled 13C-NMR spectroscopy enhances the signals from carbon atoms with a larger number of hydrogen atoms attached to them more than from carbon atoms with a smaller number of H's, and because full relaxation of 13C nuclei is usually not attained, and the nuclei with shorter relaxation times produce more intense signals.

Proton nuclear magnetic resonance is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of its molecules. In samples where natural hydrogen (H) is used, practically all the hydrogen consists of the isotope ¹H.

The heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment, normally abbreviated as HSQC, is used frequently in NMR spectroscopy of organic molecules and is of particular significance in the field of protein NMR. The experiment was first described by Geoffrey Bodenhausen and D. J. Ruben in 1980. The resulting spectrum is two-dimensional (2D) with one axis for proton (¹H) and the other for a heteronucleus, which is usually ¹³C or ¹⁵N. The spectrum contains a peak for each unique proton attached to the heteronucleus being considered. The 2D HSQC can also be combined with other experiments in higher-dimensional NMR experiments, such as NOESY-HSQC or TOCSY-HSQC.

Two-dimensional nuclear magnetic resonance spectroscopy is a set of nuclear magnetic resonance spectroscopy (NMR) methods which give data plotted in a space defined by two frequency axes rather than one. Types of 2D NMR include correlation spectroscopy (COSY), J-spectroscopy, exchange spectroscopy (EXSY), and nuclear Overhauser effect spectroscopy (NOESY). Two-dimensional NMR spectra provide more information about a molecule than one-dimensional NMR spectra and are especially useful in determining the structure of a molecule, particularly for molecules that are too complicated to work with using one-dimensional NMR.

In a chemical analysis, the internal standard method involves adding the same amount of a chemical substance to each sample and calibration solution. The internal standard responds proportionally to changes in the analyte and provides a similar, but not identical, measurement signal. It must also be absent from the sample matrix to ensure there is no other source of the internal standard present. Taking the ratio of analyte signal to internal standard signal and plotting it against the analyte concentrations in the calibration solutions will result in a calibration curve. The calibration curve can then be used to calculate the analyte concentration in an unknown sample.

Insensitive nuclei enhancement by polarization transfer (INEPT) is a signal enhancement method used in NMR spectroscopy. It involves the transfer of nuclear spin polarization from spins with large Boltzmann population differences to nuclear spins of interest with lower Boltzmann population differences. INEPT uses J-coupling for the polarization transfer in contrast to Nuclear Overhauser effect (NOE), which arises from dipolar cross-relaxation. This method of signal enhancement was introduced by Ray Freeman in 1979. Due to its usefulness in signal enhancement, pulse sequences used in heteronuclear NMR experiments often contain blocks of INEPT or INEPT-like sequences.

In nuclear chemistry and nuclear physics, J-couplings are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins that arises from hyperfine interactions between the nuclei and local electrons. In NMR spectroscopy, J-coupling contains information about relative bond distances and angles. Most importantly, J-coupling provides information on the connectivity of chemical bonds. It is responsible for the often complex splitting of resonance lines in the NMR spectra of fairly simple molecules.

Nuclear magnetic resonance (NMR) in the geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR). EFNMR is a special case of low field NMR.

In vivo magnetic resonance spectroscopy (MRS) is a specialized technique associated with magnetic resonance imaging (MRI).

Phosphorus-31 NMR spectroscopy is an analytical chemistry technique that uses nuclear magnetic resonance (NMR) to study chemical compounds that contain phosphorus. Phosphorus is commonly found in organic compounds and coordination complexes, making it useful to measure ³¹P NMR spectra routinely. Solution ³¹P-NMR is one of the more routine NMR techniques because ³¹P has an isotopic abundance of 100% and a relatively high gyromagnetic ratio. The ³¹P nucleus also has a spin of 1/2, making spectra relatively easy to interpret. The only other highly sensitive NMR-active nuclei spin 1/2 that are monoisotopic are ¹H and ¹⁹F.

Fluorine-19 nuclear magnetic resonance spectroscopy is an analytical technique used to detect and identify fluorine-containing compounds. ¹⁹F is an important nucleus for NMR spectroscopy because of its receptivity and large chemical shift dispersion, which is greater than that for proton nuclear magnetic resonance spectroscopy.

Nuclear magnetic resonance decoupling is a special method used in nuclear magnetic resonance (NMR) spectroscopy where a sample to be analyzed is irradiated at a certain frequency or frequency range to eliminate fully or partially the effect of coupling between certain nuclei. NMR coupling refers to the effect of nuclei on each other in atoms within a couple of bonds distance of each other in molecules. This effect causes NMR signals in a spectrum to be split into multiple peaks. Decoupling fully or partially eliminates splitting of the signal between the nuclei irradiated and other nuclei such as the nuclei being analyzed in a certain spectrum. NMR spectroscopy and sometimes decoupling can help determine structures of chemical compounds.

Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics and crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).

A Benchtop nuclear magnetic resonance spectrometer refers to a Fourier transform nuclear magnetic resonance (FT-NMR) spectrometer that is significantly more compact and portable than the conventional equivalents, such that it is portable and can reside on a laboratory benchtop. This convenience comes from using permanent magnets, which have a lower magnetic field and decreased sensitivity compared to the much larger and more expensive cryogen cooled superconducting NMR magnets. Instead of requiring dedicated infrastructure, rooms and extensive installations these benchtop instruments can be placed directly on the bench in a lab and moved as necessary. These spectrometers offer improved workflow, even for novice users, as they are simpler and easy to use. They differ from relaxometers in that they can be used to measure high resolution NMR spectra and are not limited to the determination of relaxation or diffusion parameters.

<span class="mw-page-title-main">Paramagnetic nuclear magnetic resonance spectroscopy</span> Spectroscopy of paramagnetic compounds via NMR

Paramagnetic nuclear magnetic resonance spectroscopy refers to nuclear magnetic resonance (NMR) spectroscopy of paramagnetic compounds. Although most NMR measurements are conducted on diamagnetic compounds, paramagnetic samples are also amenable to analysis and give rise to special effects indicated by a wide chemical shift range and broadened signals. Paramagnetism diminishes the resolution of an NMR spectrum to the extent that coupling is rarely resolved. Nonetheless spectra of paramagnetic compounds provide insight into the bonding and structure of the sample. For example, the broadening of signals is compensated in part by the wide chemical shift range (often 200 ppm in ¹H NMR). Since paramagnetism leads to shorter relaxation times (T₁), the rate of spectral acquisition can be high.

Nitrogen-15 nuclear magnetic resonance spectroscopy is a version of nuclear magnetic resonance spectroscopy that examines samples containing the ¹⁵N nucleus. ¹⁵N NMR differs in several ways from the more common ¹³C and ¹H NMR. To circumvent the difficulties associated with measurement of the quadrupolar, spin-1 ¹⁴N nuclide, ¹⁵N NMR is employed in samples for detection since it has a ground-state spin of ½. Since¹⁴N is 99.64% abundant, incorporation of ¹⁵N into samples often requires novel synthetic techniques.

<span class="mw-page-title-main">Platinum-195 nuclear magnetic resonance</span>

Platinum-195 nuclear magnetic resonance spectroscopy is a spectroscopic technique which is used for the detection and characterisation of platinum compounds. The sensitivity of the technique and therefore its diagnostic utility have increased significantly starting from the 1970s, with ¹⁹⁵Pt NMR nowadays considered the method of choice for structural elucidation of Pt species in solution.

References

↑ Silverstein; Bassler; Morrill (1981). Spectrometric Identification of organic Compounds (4th ed.). ISBN 978-0-471-09070-0.
↑ Kemp, William (1987). Organic Spectroscopy (3rd ed.). ISBN 978-0-333-41767-6.
↑ Balei, Metin. Basic ¹H and ¹³C-NMR spectroscopy. ISBN 978-0-444-51811-8.
↑ "Chemical Shift". NMRCentral. Archived from the original on 26 September 2011.
1 2 3 4 5 6 7 8 9 10 11 12 Harris, R. K.; Becker, E. D.; Cabral de Menezes, S. M.; Goodfellow, R.; Granger, P. (2001). "NMR nomenclature. Nuclear spin properties and conventions for chemical shifts (IUPAC Recommendations 2001)". Pure Appl. Chem. 73 (11): 1795–1818. doi: 10.1351/pac200173111795 .
↑ Gottlieb, Hugo E.; Kotlyar, Vadim; Nudelman, Abraham (1997). "NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities". The Journal of Organic Chemistry. 62 (21): 7512–7515. doi:10.1021/jo971176v. ISSN 0022-3263. PMID 11671879.
↑ Fulmer, Gregory R.; Miller, Alexander J. M.; Sherden, Nathaniel H.; Gottlieb, Hugo E.; Nudelman, Abraham; Stoltz, Brian M.; Bercaw, John E.; Goldberg, Karen I. (10 May 2010). "NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist" (PDF). Organometallics. 29 (9): 2176–2179. doi:10.1021/om100106e. ISSN 0276-7333.
1 2 3 4 Harris, Robin K.; Becker, Edwin D.; Menezes, Cabral de; M, Sonia; Granger, Pierre; Hoffman, Roy E.; Zilm, Kurt W. (2008). "Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)". Pure and Applied Chemistry. 80 (1): 59–84. doi: 10.1351/pac200880010059 . ISSN 0033-4545.
1 2 Rosenau, Carl Philipp; Jelier, Benson J.; Gossert, Alvar D.; Togni, Antonio (16 May 2018). "Exposing the Origins of Irreproducibility in Fluorine NMR Spectroscopy". Angewandte Chemie International Edition. 51 (30): 9528–9533. doi:10.1002/anie.201802620. ISSN 1433-7851. PMID 29663671.
1 2 Rosenau, Carl Philipp; Jelier, Benson J.; Gossert, Alvar D.; Togni, Antonio (16 May 2018). "Fluor-NMR-Spektroskopie rekalibriert". Angewandte Chemie (in German). 130 (30): 9672–9677. Bibcode:2018AngCh.130.9672R. doi:10.1002/ange.201802620. ISSN 0044-8249.
↑ CRC Handbook of Chemistry and Physics (65th ed.).
↑ Morris, Gareth A.; Jerome, Neil P.; Lian, Lu-Yun (17 February 2003). "Real‐Time Chemical‐Shift Scaling in High‐Resolution NMR Spectroscopy". Angewandte Chemie (in German). 115 (7): 847–849. doi:10.1002/ange.200390189.
↑ Glanzer, Simon; Zangger, Klaus (13 April 2015). "Visualizing Unresolved Scalar Couplings by Real-Time-Upscaled NMR". Journal of the American Chemical Society. 137 (15): 5163–5169. doi:10.1021/jacs.5b01687. PMC 4415032 . PMID 25837306.
↑ Nagaoka, Shin'ichi (May 2007). "A Short History of Three Chemical Shifts". J. Chem. Educ. 84 (5): 801. Bibcode:2007JChEd..84..801N. doi:10.1021/ed084p801.

External links

chem.wisc.edu
BioMagResBank
NMR Table
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 (see also this link for more background information on spin-spin coupling)
- Problem set 2
- Problem set 4
- Problem set 5
- Combined solutions to problem set 5 (Problems 1–32) and (Problems 33–64)

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Text is available under the CC BY-SA 4.0 license; additional terms may apply.
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[1] Silverstein; Bassler; Morrill (1981). Spectrometric Identification of organic Compounds (4th ed.). ISBN 978-0-471-09070-0.

[2] Kemp, William (1987). Organic Spectroscopy (3rd ed.). ISBN 978-0-333-41767-6.

[3] Balei, Metin. Basic ¹H and ¹³C-NMR spectroscopy. ISBN 978-0-444-51811-8.

[4] "Chemical Shift". NMRCentral. Archived from the original on 26 September 2011.

[:0-5] 1 2 3 4 5 6 7 8 9 10 11 12 Harris, R. K.; Becker, E. D.; Cabral de Menezes, S. M.; Goodfellow, R.; Granger, P. (2001). "NMR nomenclature. Nuclear spin properties and conventions for chemical shifts (IUPAC Recommendations 2001)". Pure Appl. Chem. 73 (11): 1795–1818. doi: 10.1351/pac200173111795 .

[6] Gottlieb, Hugo E.; Kotlyar, Vadim; Nudelman, Abraham (1997). "NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities". The Journal of Organic Chemistry. 62 (21): 7512–7515. doi:10.1021/jo971176v. ISSN 0022-3263. PMID 11671879.

[7] Fulmer, Gregory R.; Miller, Alexander J. M.; Sherden, Nathaniel H.; Gottlieb, Hugo E.; Nudelman, Abraham; Stoltz, Brian M.; Bercaw, John E.; Goldberg, Karen I. (10 May 2010). "NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist" (PDF). Organometallics. 29 (9): 2176–2179. doi:10.1021/om100106e. ISSN 0276-7333.

[:1-8] 1 2 3 4 Harris, Robin K.; Becker, Edwin D.; Menezes, Cabral de; M, Sonia; Granger, Pierre; Hoffman, Roy E.; Zilm, Kurt W. (2008). "Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)". Pure and Applied Chemistry. 80 (1): 59–84. doi: 10.1351/pac200880010059 . ISSN 0033-4545.

[:2-9] 1 2 Rosenau, Carl Philipp; Jelier, Benson J.; Gossert, Alvar D.; Togni, Antonio (16 May 2018). "Exposing the Origins of Irreproducibility in Fluorine NMR Spectroscopy". Angewandte Chemie International Edition. 51 (30): 9528–9533. doi:10.1002/anie.201802620. ISSN 1433-7851. PMID 29663671.

[:3-10] 1 2 Rosenau, Carl Philipp; Jelier, Benson J.; Gossert, Alvar D.; Togni, Antonio (16 May 2018). "Fluor-NMR-Spektroskopie rekalibriert". Angewandte Chemie (in German). 130 (30): 9672–9677. Bibcode:2018AngCh.130.9672R. doi:10.1002/ange.201802620. ISSN 0044-8249.

[11] CRC Handbook of Chemistry and Physics (65th ed.).

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