Fourier transform NMR spectrum

Figure 4. Proton-noise decoupled, Fourier transform NMR spectrum of Rh(ttp)HCl(CHsCN) -BF in CDsCN...

Figure 5. Proton-coupled NMR spectrum of the major metabolite Isolated from P. putida after a 24 hour incubation with 4-deoxy-4-fluoro-D- (U-glucose. The carbon-13 Fourier transformed NMR spectrum was obtained with a 300 MHz General Electric NMR spectrometer after 36000 scans in D2O. Chemical shift values (PPM) are relative to tetramethylsllane.

Figure 7. Proton Fourier transformed NMR spectrum of the major metabolite isolated from P. putida after 2k...

Figure 1.14. Solid-state 22.6 MHz Fourier-transform NMR spectrum of Suwanee River standard humic acid. Reprinted with permission from Organic Geochemistry, Vol. 11, Leenheer et al. Presence and Potential Significance of Aromatic-Ketone Groups in Aquatic Humic Substances, Copyright 1987, Pergamon Press PLC.

In the Fourier transform NMR spectrum of polyhexafluorpropylene-vinylidene fluoride copolymer, the lines observed are attributed to the following CF3 group (6 = -70 to -75), CF2 group (6 = -90 to -120), and CF group (6 = -180 to -185). The results of the determination for a copolymer sample are given in Table 3.8. The values obtained are in excellent agreement with those obtained by mass balance. 

The NMR spectrum of calcitriol, recorded on a Varian XL-100/Nicolet TT-100 pulsed Fourier Transform NMR spectrometer, with internal deuterium lock, is shown in Figure 2 (2). The spectrum was recorded using a solution of 0.84 mg of sample dissolved in 50 microliters of CD OD (100%D) containing 1% v/v tetramethylsilane in a 1.7 mm capillary tube. The spectral assignments are given in Table I. 

All facets of study have been greatly aided by the ease with which crystal structures may be obtained and by the availability of sensitive Fourier transform NMR spectrometers which allow nuclei such as l70, 51V, wNb, s5Mo, and, K3W to be used for structural studies. Oxygen-17 NMR spectroscopy has proved to be particularly useful because 170 chemical shifts are very sensitive to environment. As a result it is possible to distinguish between terminal and various kinds of bridging oxygen sites. The l70 spectrum of [W Oi, ]2 and its structure are shown in Fig. Ifi-IOa/1 We see... 

Fourier transform NMR spectroscopy, on the other hand, permits rapid scanning of the sample so that the NMR spectrum can be obtained within a few seconds. FT-NMR experiments are performed by subjecting the sample to a very intense, broad-band, Hl pulse that causes all of the examined nuclei to undergo transitions. As the excited nuclei relax to their equilibrium state, their relaxation-decay pattern is recorded. A Fourier transform is performed upon this relaxation-decay pattern to provide the NMR spectra. The relaxation-decay pattern, which is in the time domain, is transformed into the typical NMR spectrum, the frequency domain. The time required to apply the Hl pulse, allow the nuclei to return to equilibrium, and have the computer perform the Fourier transforms on the relaxation-decay pattern often is only a few seconds. Thus, compared to a CW NMR experiment, the time can be reduced by a factor of 1000-fold or more by using the FT-NMR technique. 

In an ordinary Fourier transform NMR experiment the time-domain signal (the FID) is converted into a frequency-domain representation (the spectrum) thus a function of time, S(t2), is converted into a function of frequency, S(f2). The very simple basic idea of 2D NMR is to treat the period preceding the recording of the FID (known as the evolution period ) as the second time variable. During this period, tu the nuclear spins are manipulated in various ways. In the 2D experiment a series of S(t2) FID s are recorded, each for a different t u and the result is considered a function of both time variables, S(tu t2). A twofold application of the Fourier transformation (see Fig. 82) then yields a 2D spectrum, S(fi,f2), which has two frequency... 

The broad band decoupled carbon-13 NMR spectrum of cimetidine hydrochloride (Figure 3) was obtained by using a solution of approximately 100 mg/ml in deuterated dimethylsulf oxide. The deuterium signal of dimethylsulfoxide was used as the internal reference and the spectrum was obtained on a Varian Associates Model FT-80 fourier transform NMR spectrometer. The chemical shift assignments are ... 

Any modern Fourier transform NMR spectrometer manufactured in the 1980s by major instrument companies is capable of performing various types of H NMR experiments needed for studies of hemoglobin. With a modern 7.0-Tesla high-resolution NMR spectrometer operating at 300 MHz for H, a satisfactory H NMR spectrum (with a signal-to-noise ratio of 20 or better) of 0.3—0.5 ml Hb in millimolar concentration contained in a 5-mm sample tube can be obtained in a few minutes. 

The actual Fourier transform is a digital calculation, so not all frequencies are tested. In fact, the number of frequencies tested is exactly equal to the number of time values sampled in the FID. If we start with 16,384 complex data points in our FID (16,384 real data points and 16,384 imaginary data points), we will end up with 16,384 data points in the real spectrum (the imaginary spectrum is discarded). Another difference from the above description is that the actual Fourier transform algorithm used by computers is much more efficient than the tedious process of multiplying test functions, one by one, and calculating the area under the curve of the product function. This fast Fourier transform (FFT) algorithm makes the whole process vastly more efficient and in fact makes Fourier transform NMR possible. 

The development of Fourier transform NMR spectroscopy made carbon NMR (13C NMR or CMR) possible, and high-field superconducting spectrometers allowed it to become nearly as convenient as proton NMR ( H NMR). Carbon NMR determines the magnetic environments of the carbon atoms themselves. Carbonyl carbon atoms, alkyne carbon atoms, and aromatic carbon atoms all have characteristic chemical shifts in the 13C NMR spectrum. 

Fourier transform NMR spectroscopy. The FT NMR spectrometer delivers a radio-frequency pulse close to the resonance frequency of the nuclei. Each nucleus precesses at its own resonance frequency, generating a free induction decay (FID). Many of these transient FIDs are accumulated and averaged in a short period of time. A computer does a Fourier transform (FT) on the averaged FID, producing the spectrum recorded on the printer. 

Early studies were made by continuous wave 119Sn NMR, and later by intemuclear 1H 119Sn double resonance (INDOR), in which a tin satellite line in the proton NMR spectrum is monitored as the region of the tin resonance frequency is simultaneously swept.41 42 Since the introduction of pulsed Fourier transform NMR, direct observation of the 119Sn resonance has become the standard technique for measurements,37> 39 some-... 

For the example in Fig. 2, the Fourier transformed NMR spectra (variables or descriptors being intensity as a function of frequency) were utilized for the creation of the data matrix D. It should be noted that many different descriptors can be used to create D, with the descriptor selection depending on the analysis method and the information to be extracted. For example, in the spectral resolution methods (Section 6), the desired end result is the determination of the true or pure component spectra and relative concentrations present within the samples or mixtures [Eq. (4)]. For this case, the unmodified real spectra Ij co) are commonly used for the chemometric analysis. In contrast, for the non-supervised and supervised methods described in Sections 3 and 4, the classification of a sample into different categories is the desired outcome. For these types of non-supervised and supervised methods the original NMR spectrum can manipulated or transformed to produce new descriptors including... 

The principle can be understood if an NMR spectrum is considered just one line corresponds to the absorption or emission of radiofrequency radiation of just one frequency, whereas say a 1.2.1 triplet will correspond to three frequencies with amplitudes Simple Fourier transform NMR spectros-... 

In the last years the technique of Fourier transform NMR spectroscopy has become widely appreciated for its speed and increased sensitivity it has especially become the method of choice for studies of the less sensitive nuclei, such as 13C or 15 N. In principle, the same information is contained in the slow passage and Fourier-transformed, pulse-excited spectra, and each may be optimized for resolution or for studies of particular features of the spectrum. Fourier transformation is nor-... 

In one-dimensional pulsed Fourier transform NMR the signal is recorded as a function of one time variable and then Fourier transformed to give a spectrum which is a function of one frequency variable. In two-dimensional NMR the signal is recorded as a function of two time variables, q and q, and the resulting data Fourier transformed twice to yield a spectrum which is a function of two frequency variables. The general scheme for two-dimensional spectroscopy is... 

In modern instruments, the magnetic field is kept constant, and the radiofrequency is varied in pulse Fourier transform NMR (FT-NMR). In FT-NMR, all of the nuclear spins are excited instantaneously using a mixture of radiofrequencies. The spectrum is obtained by analysing the emission of radiofrequency energy (as the spins return to equilibrium) as a function of time. 

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