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Off Resonance Decoupling
ทาให้ทราบว่า C แต่ละตัว จับกับ H กี่ตวั ตามกฏ n+1 rule
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A Quick Dip Into DEPT
Distortionless Enhancement by Polarization Transfer
-Mordern method of off-resonance
-Requires an FT-pulsed spectrometer
(+) –CH or –CH3
(-) –CH2
-CH
protonated C
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Compounds with Aromatic Rings
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Introduction to 2D NMR spectroscopy
COSY
The basic 2D NMR experiment based on through-bond scalar coupling is COSY(COrrelated SpectroscopY). The COSY
experiment has the simplest pulse sequence of all 2D NMR experiments. The pulse sequence is shown in Figure 1.1.
Figure 1.1: The pulse sequence of the 2D correlated spectroscopy (COSY). Two 90-degree pulses are separated by the
mixing period .
In this experiment the spins undergo precession about one another, in addition to the usual precession about the applied
magnetic field. During the mixing period, i.e., the second pulse, of this experiment, J-coupled spins exchange coherence
and communicate the information about their precession frequencies. The result, for the COSY experiment, is that a
cross peak between two spins, i, and j, will occur in the spectrum if spin i and j are directly coupled to one another.
The cross peaks in COSY spectra are antiphase in character, that is, half of the multiplet is "up" and the other half is
"down" as shown in a simulated 2D COSY spectrum in Figure 1.2.
Figure 1.2: Simulated 2D COSY contour plot of two coupling spins. Open circles with solid and dashed lines are cross
peaks with positive and negative intensity, respectively. The dispersive diagonal peaks are represented by filled circles.
This feature increases the difficulties of doing automated peak picking. To determine the center of each cross peak, two
local maxima and minima have to be found which is difficult in a severely overlapped spectrum.
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2-nitropropane
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Isopentyl acetate
Isopentyl acetate
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citronellol
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HETCOR(HETeronuclear chemical shift CORrelation)
HMQC (Heteronuclear Multiple Quantum Correlation) and HSQC (Heteronuclear
Single Quantum Correlation) experiments correlate the chemical shift of proton
with the chemical shift of the directly bonded carbon (or nitrogen). This experiment
utilizes one-bond couplings
2-nitropropane
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Isopentyl acetate
4-methyl-2-pentanol
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