Understanding NMR Spectroscopy phần 7 ppsx

... uses coherence transfer pathways to specify the desired outcome of the experiment. 9.2 Phase in NMR In NMR we have control over both the phase of the pulses and the receiver phase. The effect of ... Coherence Selection: Phase Cycling and Gradient Pulses † 9.1 Introduction The pulse sequence used in an NMR experiment is carefully designed to produce a particular outcome. For example, we...

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... –90 270 3 180 –180 0 0 –180 180 4 270 – 270 0 0 – 270 90 5 0 0 90 180 180 180 6 90 –90 90 180 90 90 7 180 –180 90 180 0 0 8 270 – 270 90 180 –90 270 9 0 0 180 360 360 0 10 90 –90 180 360 270 270 11 ... 270 11 180 –180 180 360 180 180 12 270 – 270 180 360 90 90 13 0 0 270 540 540 180 14 90 –90 270 540 450 90 15 180 –180 270 540 360 0 16 270 – 270 270 540 270 270 In the first four steps...

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... 2002 Understanding NMR Spectroscopy James Keeler University of Cambridge, Department of Chemistry c  James Keeler, 2002 2–10 NMR and energy levels ααα αβα ββα βαα 1 23 4 ααβ αββ βββ βαβ 5 67 8 Fig. ... protons γ =+2. 67 × 10 8 rad s −1 T −1 , so in a magnetic field of 4 .7 T the Larmor frequency of a spin with chemical shift zero is ν 0 =− 1 2π γ(1 + δ) B 0 =− 1 2π × 2. 67 × 10 8...

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... be “phase shifted by 90 ◦ ”(wetakean 2–18 NMR and energy levels 2 .7 Exercises E 2–1 In a proton spectrum the peak from TMS is found to be at 400.13 570 5 MHz. What is the shift, in ppm, of a peak ... most basic pulsed NMR ex- periment works, let alone the large number of subtle two-dimensional exper- iments which have been developed. To make any progress in understanding NMR experim...

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... are very useful for NMR. To maintain the wire in its superconducting state the coil is immersed in a bath of liquid helium. Surrounding this is usually a “heat shield” kept at 77 K by contact with ... by 45 ◦ may enhance the resolution but use of a sine bell shifted by 90 ◦ does not. E 4 7 In a proton NMR spectrum the peak from TMS was found to show “wig- 4 Fourier transformation and da...

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... described in section 4.1). Such a quadrature detection scheme is the norm for all modern NMR spectrometers. 5 .7 Time and frequency We are now in a position to tidy up a number of points of terminology ... and anti- phase magnetization according to the following diagrams 5.4 The receiver 5 7 5.4 The receiver The NMR signal emanating from the probe is very small (of the order of µV) but...

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... case of one-dimensional spectra. Usually, NMR data processing software provides options for making such phase corrections to two-dimensional data sets. 7 27 In practice it is usually more convenient ... the spectral width is doubled all peaks are represented correctly – spectrum c. 7 23 7. 6.2 Two-dimensional spectra 7. 6.2.1 Phase and amplitude modulation There are two basic types of...

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... receiver phase from all of the pulses. So, for example, in step 2 we subtract 270 ° from the pulse phases to give – 270 °, – 270 ° and –180° for the phases of the first three pulses, respectively; reducing ... Ser. A 105, 1 67- 183 (1993) ). Here, we note the following features. (a) The optimum dephasing is obtained when the extra offset induced 9–29 doubles the length of the phase cycle. 9.5...

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... a function of the delay, t, in the sequence: t / s 0.1 0.5 0.9 1.3 1 .7 2.1 2.5 2.9 S –98.8 –3.4 52.2 82.5 102 .7 115.2 120 .7 125.1 The peak height after a single 90° pulse was measured as 130.0 ... Start from the expression in the middle of page 7 10, section 7. 4.21. [You will need the identity cos sin sin sinAB BA BA=+ () +− () [] 1 2 ]. *E7-6. Consider the COSY spectrum for a three-...

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... following oxygen administration in healthy young adults. Physiology and Behavior, 67, 78 3 78 9. Cognitive enhancers 2 17 can be seen that, up to a point, baseline levels of metabolism allow cognitive ... Journal of Neuroscience, 96, 2 17 224. Foster JK, Lidder PG and Su ¨ nram SI (1998). Glucose and memory: Fractionation of enhance- ment effects? Psychopharmacology, 13, 259– 270 . Hogervors...

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