Name: 2d nmr correlation paths in molecules
Uploaded: 2024-12-05T18:32:26.000Z
Duration: 1 min 16 s
Channel: JoVE

Homonuclear 2D experiments measure differences in magnetic environment for a single TYPE of nuclei.
The standard proton COSY-90 employs a second 90-degree pulse to reveal through-bond structural relationships between protons separated by two to three bonds.
In contrast, COSY-45 applies a 45-degree pulse, sacrificing intensity for better detail and resolution.
Long-range or LR-COSY experiments extend the evolution and detection periods to identify correlations not visible in standard COSY.
Relayed COSY adds extra pulses to the standard pulse sequence to produce cross peaks between cross peaks, showing specific molecular connections hidden by overlapping signals.
However, the total correlation spectroscopy experiment reveals all through-bond proton correlations within a spin system, providing data as though from simultaneous COSY, LR-COSY, and relayed COSY experiments.
Meanwhile, correlations between spatially close yet non-coupled protons are revealed through Nuclear Overhauser Effect Spectroscopy.

2d nmr: overview of homonuclear correlation techniques

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that utilizes a second 90-degree pulse to achieve high sensitivity and resolution. It excels in analyzing small to medium-sized molecules and provides information on directly coupled protons. COSY45, similar to COSY90, uses 45-degree pulses instead of 90-degree pulses. This results in reduced sensitivity but improved resolution.
Long-range COSY (LR-COSY) extends the COSY experiment to detect scalar couplings between nuclei further apart in the molecule. It achieves this by combining multiple pulse sequences and magnetization transfers.
Relayed COSY is a variant of COSY that adds extra pulses to the standard pulse sequence to produce cross-peaks between cross-peaks, showing specific molecular connections hidden by overlapping signals.
TOCSY (Total Correlation Spectroscopy), also known as HOHAHA (Homonuclear Hartmann-Hahn Spectroscopy), reveals all through-bond connectivity between all coupled nuclei. TOCSY is especially useful for analyzing molecules with overlapping signals and complex coupling patterns.
NOESY (Nuclear Overhauser Effect Spectroscopy) measures the nuclear overhauser effect, which arises from dipole-dipole interactions between nuclei. It provides information about spatial proximity and can be used to determine the three-dimensional structure of a molecule.
ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) is similar to NOESY but employs a different mechanism to obtain through-space correlations. It provides information about spatial proximity and is particularly useful for studying molecules with weak NOE signals.
In conclusion, choosing a COSY variant depends on the molecule or reaction under investigation and the desired information. The right COSY variant can be determined based on molecular size, coupling complexity, and the need for spatial or long-range connectivity data.

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations ...

2d-nmr-overview-of-homonuclear-correlation-techniques

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Analytical Chemistry

Unit 1

Advanced Nuclear Magnetic Resonance Spectroscopy

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KEY TERMS AND CONCEPTS

2d nmr correlation paths in molecules

2D NMR homonuclear correlation techniques show how nuclei of the same type connect within a molecule. In nuclear magnetic resonance (NMR) spectroscopy, these methods reveal scalar couplings, which are interactions between nearby nuclei through bonds. That information helps identify which atoms are linked and how a molecule is put together.

COSY is the main homonuclear correlation experiment. COSY90 is the standard 2D COSY method and uses a second 90-degree pulse to improve sensitivity and resolution. It is well suited for small to medium-sized molecules and shows directly coupled protons.

COSY45 works in a similar way but uses 45-degree pulses instead of 90-degree pulses. This lowers sensitivity, but it can improve resolution. Long-range COSY, or LR-COSY, is designed to detect scalar couplings between nuclei that are farther apart in the molecule. It does this by combining multiple pulse sequences and magnetization transfers.

Relayed COSY adds extra pulses to the usual COSY sequence. It creates cross-peaks between cross-peaks, which can expose molecular connections that are hidden when signals overlap. TOCSY, or total correlation spectroscopy, is also called HOHAHA, short for homonuclear Hartmann-Hahn spectroscopy. It shows through-bond connectivity among all coupled nuclei and is especially useful for complex coupling patterns and overlapping signals.

Other homonuclear methods focus on space instead of bonds. NOESY measures the nuclear Overhauser effect, which comes from dipole-dipole interactions between nuclei, and it gives information about spatial proximity. ROESY is similar to NOESY but uses a different mechanism to produce through-space correlations. It is useful when NOE signals are weak.

The best COSY variant depends on the molecule being studied and the information needed. Some experiments work better for molecular size, while others are better for coupling complexity, long-range links, or spatial structure. Choosing the right method helps reveal the most useful NMR data for a reaction or molecule.

2D NMR Correlation Paths in Molecules

&sup1;h nmr of conformationally flexible molecules: temporal resolution

h-nmr-of-conformationally-flexible-molecules-temporal-resolution

¹H NMR Ring Flips and Signal Averaging

¹H NMR can show how fast molecular motion changes the signals we see. In cyclohexane, the chair form flips rapidly between two equivalent chair conformers at room temperature. This happens about 10^5 times per second, and the two shapes stay in equilibrium. During ring flipping, an axial proton becomes equatorial, and an equatorial proton becomes axial. These changes are too fast to detect on the NMR timescale. As a result, the NMR spectrometer cannot tell the axial and equatorial protons...

&sup1;h nmr of conformationally flexible molecules: variable-temperature nmr

h-nmr-of-conformationally-flexible-molecules-variable-temperature-nmr

Cyclohexane Ring Flipping in Variable-Temperature NMR

Cyclohexane ring flipping can be tracked with variable-temperature NMR. The experiment helps distinguish the axial and equatorial protons in a deuterium-substituted cyclohexane sample. Deuterium is used to replace eleven of the twelve protons. This reduces possible peak splitting from spin-spin coupling between neighboring protons. The remaining proton shifts between the axial and equatorial positions as the chair form of cyclohexane changes. At room temperature, ring flipping is very fast, so...

&sup1;h nmr of labile protons: temporal resolution

h-nmr-of-labile-protons-temporal-resolution

OH Proton Exchange in Ethanol NMR

The OH proton in alcohols can shift and split differently in a proton NMR spectrum. Its position usually falls around 2 to 5 ppm, but the exact value depends on the alcohol and the sample conditions. This proton is labile, which means it can exchange rapidly with other molecules. Hydrogen bonding to oxygen or nitrogen changes the electron density around the proton. That change affects the chemical shift seen in the proton NMR spectrum. The exchange rate also affects spin-spin coupling between...

&sup1;h nmr of labile protons:  deuterium (&sup2;h) substitution

h-nmr-of-labile-protons-deuterium-h-substitution

Using D2O to Identify OH Protons

Deuterium substitution can help identify labile protons in ¹H NMR spectra. Labile protons are hydrogens that can be replaced by another hydrogen isotope. In this lesson, deuterium is used to simplify the spectrum of ethanol. Deuterium, or ²H, is one of the three isotopes of hydrogen. Its nucleus contains one proton and one neutron. When D₂O is added to a pure dry ethanol solution, the labile proton on the –OH group is replaced by deuterium. A proton NMR spectrum does not show signals from...

nuclear overhauser enhancement (noe)

Using NOE to Map Nearby Nuclei

Nuclear Overhauser enhancement, or NOE, shows how irradiation of one spin-active nucleus can change the signal of nearby nuclei. These nuclei do not have to be chemically bonded or connected through J-coupling. The effect comes from through-space interactions between nuclear spins. NOE gets weaker as the distance between nuclei increases. It is generally not observed beyond about 4 angstroms. Dipole-dipole interactions between neighboring spin-active nuclei transfer nuclear spin polarization,...

insensitive nuclei enhanced by polarization transfer (inept)

insensitive-nuclei-enhanced-by-polarization-transfer-inept

NMR Signal Boosting with INEPT Pulses

INEPT is an NMR method that boosts weak signals from low-abundance nuclei. It is used to detect nuclei such as carbon-13 and nitrogen-15 in small molecules. The goal is to make these hard-to-see nuclei easier to observe in an NMR spectrum. The technique works by transferring polarization from a more abundant nucleus, usually hydrogen-1, to the nucleus of interest. Hydrogen-1 has higher receptivity, so it can provide the starting signal boost. Spin coupling then helps move that polarization to...

double resonance techniques: overview

Spin Decoupling in NMR Spectroscopy

Spin decoupling is a key use of double resonance in nuclear magnetic resonance (NMR) spectroscopy. It uses two radiofrequency pulses or frequencies at the same time to act on two different nuclear spins. This makes the spectrum simpler and easier to read. In spin decoupling, one type of nucleus is selectively suppressed while the signal from another nucleus is observed. The radiofrequency pulse sequence removes the coupling with one nuclide and can greatly improve resolution. As a result, the...

two-dimensional (2d) nmr: overview

2D NMR Spectra and Signal Mapping

Two-dimensional (2D) NMR helps make sense of crowded NMR data from large and complex molecules, such as natural products. A 1D NMR spectrum can have overlapping signals and complicated splitting patterns. 2D NMR adds a second frequency axis, which helps show the coupling information between nucleus A and nucleus B in a molecule. 2D spectra are built in four steps. First is the preparation period, when nucleus A is excited with a radiofrequency pulse. Next is the evolution, or wait, period t1.

2D NMR homonuclear correlation techniques show how nuclei of the same type connect within a molecule. In nuclear magnetic resonance (NMR) spectroscopy, these methods reveal scalar couplings, which are interactions between nearby nuclei through bonds. That information helps identify which atoms are linked and how a molecule is put together. COSY is the main homonuclear correlation experiment. COSY90 is the standard 2D COSY method and uses a second 90-degree pulse to improve sensitivity and...

2d nmr: homonuclear correlation spectroscopy (cosy)

2d-nmr-homonuclear-correlation-spectroscopy-cosy

Reading Proton Coupling with COSY Maps

COSY is a 2-dimensional NMR method that shows which protons are coupled to each other. It is used to spot geminal and vicinal coupling in a sample. This makes it helpful for reading proton relationships in complex spectra. The ethyl acetate example shows how COSY is built from the 1D proton NMR spectrum. The same chemical shift scale appears on both the vertical and horizontal axes. The peaks along the diagonal are called diagonal peaks, and they match the three peaks seen in the 1D proton...

2d nmr: overview of heteronuclear correlation techniques

2d-nmr-overview-of-heteronuclear-correlation-techniques

2D NMR Correlation Peaks and Bond Links

Heteronuclear correlation spectroscopy is a 2D NMR method that links different nuclei, usually a proton and an X-nucleus such as carbon-13 or nitrogen-15. It helps scientists study the structure and composition of complex chemical compounds. In a heteronuclear correlation spectrum, one axis shows X-nucleus chemical shifts and the other axis shows the proton spectrum. Cross-peaks mark which protons are connected to which X-nuclei. The main heteronuclear correlation experiments are HETCOR, HSQC,...

2d nmr: heteronuclear single-quantum correlation spectroscopy (hsqc)

2d-nmr-heteronuclear-single-quantum-correlation-spectroscopy-hsqc

HSQC NMR Maps Carbon-Proton Connections

HSQC NMR maps the direct links between hydrogen atoms and the carbons they are attached to. It is a 2D NMR method, so it shows the data on two axes instead of one. The experiment is similar to heteronuclear correlation spectroscopy, or HETCOR, but HSQC is more sensitive. In an HSQC spectrum, the proton chemical shift appears on the horizontal F2 axis. The 13C chemical shift appears on the vertical F1 axis. The spectrum also includes the matching proton and 13C spectra. The contour plot does...

key terms and concepts

Explore how COSY, TOCSY, NOESY, and ROESY reveal bond links and spatial proximity in 2D NMR. Learn which method fits different molecules.

2D NMR Correlation Paths in Molecules | JoVE K12

analytical chemistry

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2D NMR Correlation Paths in Molecules

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