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Off Resonance Decouplingที่�าให้�ที่ราบว่�า C แต่�ละต่�ว่ จั�บก�บ H ก��ต่�ว่ ต่ามกฏ n+1 rule

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A Quick Dip Into DEPTDistortionless Enhancement by Polarization Transfer-Mordern method of off-resonance-Requires an FT-pulsed spectrometer

-CH

(+) –CH or –CH3

(-) –CH2

protonated C

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Compounds with Aromatic RingsDown load ได้�ที่�� www.weerachai.tk

Introduction to 2D NMR spectroscopyCOSYThe 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 acetateDown load ได้�ที่�� www.weerachai.tk

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

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4-methyl-2-pentanol

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