二维核磁共振谱原理

2 D C-H相关谱（C-H COSY)
2 D 远程C-H COSY
HMQC and HMBC
Heteronuclear Multiple Quantum Coherence Heteronuclear Multiple Bond Coherence (HMBC): (HMQC) and
2-D inverse H,C correlation techniques that allow for the determination of carbon (or other heteroatom) to hydrogen connectivity.
HMQC is selective for direct C-H coupling
HMBC will give longer range couplings (2-4 bond coupling).
Gradient HMBC (gHMBC) improves the acquired spectra by significantly reducing unwanted signal artifacts.
There is no way to know how many bonds separate an H and C when a peak is observed, so analysis is a process of attempting to assign all observed peaks, testing for consistency and checking to be sure none of the assignments would require implausible or impossible couplings.
Because of the large number of peaks observed, analysis requires several expanded plots. In this case, the spectrum has been divided into 4 sections, each of which is discussed below.
What You See In a NOESY. . .
突出表现NOE效应的NOESY谱
NOESY. . .
NOESY Spectrum of Codeine
The sample is 3.3 mg of codeine in .65 ml CDCl3 A contour plot of the NOESY spectrum is shown below. As with all homonuclear 2D plots, the diagonal consists of intense peaks that match the normal spectrum, as do projections onto each axis. The interesting information is contained in the "cross-peaks", which appear at the coordinates of 2 protons which have an NOE correlation. For small molecules, the NOE is negative. Exchange peaks have the opposite sign from NOE peaks, making them easy to identify. The water peak at 1.5 ppm exchanges with the OH at 2.9 ppm, shown here in red. The spectrum is phased with the large diagonal peaks inverted (shown in red here), so the NOE cross-peaks are positive.
HMQC (trans-ethyl 2-butenoate)
HMQC – Heteronuclear Multiple-Quantum Coherence Experiment
HMQC – Heteronuclear Multiple-Quantum Coherence Experiment
C(9)-H C(9)-H
NOESY Spectrum of Codeine
Expansion of the upfield region:
8 - 7, 12 7 - 18, 18' 3 - 5, 10 5 - 11, 16, 18' 9 - 10, 17, 17' 10 - 16 11 - 18, 16, 14, 18' 18 - 13, 18' 16 - 14, 17 13 - 14, 17, 17' 13' - 17, 17' 17 - 17'
Compare to the spectrum obtained when the experiment is optimized for 4 Hz.
The experiment is designed to suppress 1-bond correlations, but a few are observed in most spectra. In concentrated samples of conjugated systems, 4-bond correlations can be observed.
Peaks occur at coordinates in the 2 dimensions corresponding to the chemical shifts of a carbon and protons separated by (usually) 2 or 3 bonds. The experiment is optimized for couplings of ~8 Hz. Smaller couplings are observed, but their intensities are reduced.
NOESY Spectrum of Codeine
In addition to confirming assignments, the NOESY spectrum allows stereospecific assignments of methylene Hs. The 3 crosspeaks indicated in red on the plot below distinguish between the 3 CH2 pairs: Table of NOEs: ( ' indicates the more upfield of geminal CH2 protons) 5 -18' 16 - 17 18 - 13
HMQC (1-Bond CH Correlation) of Codeine
Assign ment
1H
13C
6.6
6.5 5.7 5.3 4.8 4.2 3.8 3.3 3.0 & 2.3 2.6 2.6 & 2.4 2.4 2.0 & 1.8
113
120 133 128 91 66 56 59 20 40 46 43 36
shift Table of COSY correlations 6.6 5.7 5.7 5.7 5.3 5.3 4.9 4.2 3.3 3.3 3.3 3.0 3.0 2.6 2.6 2.6 2.4 2.4 2.1 shift 6.7 5.3 2.7 4.9 4.2 2.7 4.2 2.9 2.7 2.4 2.3 2.4 2.3 2.4 2.1 1.9 2.1 1.9 1.9 Assignments 7-8 3-5 3 - 16 3-9 weak 5 - 10 5 - 16 9 - 10 10 - OH 11- 16 11 - 14 11 - 18' 18 - 14 18 - 18' 13 - 13' 13 - 17 13 - 17' 13' - 17 13' - 17' 17 - 17'
The colored arrows trace out coupling networks, corresponding to: H-3 —> H-5 —> H-10 —> OH H-10 -> H-9 H-3 —> H-16 H-16 —> H-11
COSY Spectrum of Codeine
2D 核磁共振谱
COSY: Hypothetical Coupling
Hale Waihona Puke COSY: 1H-1H Coupling
COSY Spectrum of Codeine
Coupling "networks" can be traced out, as shown in the figure below.
8
7 3 5 9 10 12 11 18 16 13 14 17
HMBC (Multiple-Bond CH Correlation) of Codeine
This is a 2D experiment used to correlate, or connect, 1H and 13C peaks for atoms separated by multiple bonds (usually 2 or 3). The coordinates of each peak seen in the contour plot are the 1H and 13C chemical shifts. This is extremely useful for making assignments and mapping out covalent structure. The information obtained is an extension of that obtained from an HMQC spectrum, but is more complicated to analyze. Like HMQC, this is an "inverse detection" experiment, and is possible only on newer model spectrometers. Acorn NMR's new JEOL Eclipse+ 400 is equipped to perform inverse experiments, and uses Z-gradients for improved spectral quality.