Understanding NMR Spectroscopy phần 8 ppsx

... 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 11 180 – 180 ... 2 equivalent phase rx. phase to select ∆p = –3 difference 10 0 0 0 0 2 90 – 180 180 270 270 – 180 = 90 3 180 –360 0 180 180 – 0 = 180 4 270 –540 180 90 90 – 180 = –90 As before, the equiva...

Ngày tải lên: 14/08/2014, 09:21

... Pulses" © James Keeler 2001 and 2003. 8 16 8. 5 Origins of relaxation We now turn to the question as to what causes relaxation. Recall from section 8. 1 that relaxation involves transitions ... mechanical details of the interaction. For 8 8 d d z z z II t WWWWII WWSS W W IS z II z zIIzz − () =− + + + () − () −− () − () −− () () ( ) () () 0 12 20 0 20 0 12 2 8. 3.1 Interpreting th...

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... institutions and Takaful companies. The regulatory framework for these institutions is different in 388 Understanding Islamic Finance The Shar ¯ ı´ah board’s report should also include a clear statement ... EIB account; • worldwide acceptance; • a 100 % cash advance facility; • free online access; 3 78 Understanding Islamic Finance The framework of the IERS is based on the concept of Sh...

Ngày tải lên: 09/08/2014, 16:21

... 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. ... αβ−ν 0,1 − 1 2 J 12 + 1 2 J 13 6 8 ββ−ν 0,1 + 1 2 J 12 + 1 2 J 13 ααα αβα ββα βαα 1 2 3 4 ααβ αββ βββ βαβ 5 67 8 −ν 0,1 J 13 J 12 J 12 J 13 9692 1 081 04100 13 57 24 68 spin 2 s...

Ngày tải lên: 14/08/2014, 09:21

... 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 experiments we ... magnetization we must use a 180 ◦ pulse. Pulse calibration is therefore an important preliminary to any experiment. flip angle signal intensity 90º 180 º 270º π 3π/2π/2 Fig. 3. 18 Illustrati...

Ngày tải lên: 14/08/2014, 09:21

... this point. 4 .8 Truncation In conventional NMR it is virtually always possible to record the FID until it has decayed almost to zero (or into the noise). However, in multi-dimensional NMR this may ... the refocusing pulse about the −x axis be? E 3–4 The gyromagnetic ratio of phosphorus-31 is 1. 08 × 10 8 rad s −1 T −1 .This nucleus shows a wide range of shifts, covering some 700 ppm....

Ngày tải lên: 14/08/2014, 09:21

... in section 3 .8. In general the sequence – τ – 180 °(x) – τ – [6.4] refocuses any evolution due to offsets; this is a very useful feature which is much used in multiple-pulse NMR experiments. One ... probe. 5 8 How the spectrometer works to the actual waveform. (b) (a) Fig. 5.5 Digitization of a waveform using an ADC with 8 levels (3 bits). The output of the ADC can only be one of t...

Ngày tải lên: 14/08/2014, 09:21

... 8 6 Just in the same was as was done in Section 8. 2, rate equations can be written for the flow of population from any of ... below are three versions of the anti-phase multiplet for successively decreasing values of J 23 . 8 2 8. 2 Rate equations and rate constants The populations of energy levels are in many ways analogous ... 2 , () =+ {} −+ {} [] + [] + () + () − () − () + () + () s...

Ngày tải lên: 14/08/2014, 09:21

... 180 0 3 180 180 0 0 4 270 270 180 0 We can play one more trick with this phase cycle. As the third pulse is required to achieve the transformation ∆p = –3 or +1 we can alter its phase by 180 ° ... shifting the receiver by 180 ° also. Doing this for steps 2 and 4 only gives step 1st pulse 2nd pulse 3rd pulse receiver 10000 2 90 90 0 180 3 180 180 0 0 4 270 270 0 180 This is exactly the cyc...

Ngày tải lên: 14/08/2014, 09:21

... Explain. Z H A H B H C X Y E8-7. What do you understand by the terms correlation time and spectral density? Why are these quantities important in determining NMR relaxation rate constants? E8 -8. The simplest ... time, T 1 . E8-2. In an experiment to estimate T 1 using the sequence [ 180 ° – τ – 90°] acquire three peaks in the spectrum were observed to go through a null at 0.5, 0.6 and 0...

Ngày tải lên: 14/08/2014, 09:21