Decoupling homonuclear

Experiment Relative B amplitude Relative RF power 90° Pulse 

This traditional ID NMR experiment involves selectively decoupling a proton from its J coupling partners. This is accomplished by low-power irradiation at the frequency of the 

The results of a homonuclear decoupling experiment on sucrose are shown in Fig. 5.18. The experiment is set up by acquiring a normal H spectrum and determining the exact RF frequency of each peak (each resonance) we wish to test by CW irradiation during the acquisition of the FID. The desired frequencies are actually offsets from a fundamental decoupler frequency for example, an offset (Bruker o2 for channel 2 offset Varian dof for decoupler offset) of 132.6 Hz is added to the fundamental frequency (Bruker BF2 

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Figure 1.8. Homonuclear decoupling of the CH protons of 3-aminoacrolein (CDaOD, 25 C, 90 MHz), (a) H NMR spectrum (b) decoupling at Sh = 8.5 (c) decoupling at = 7.3. At the position of the decoupled signal in (b) and (c) interference beats are observed because of the superposition of the two very similar frequencies...

Assume a 180° PIP is applied at the centre of the 13CO in the middle of the 13C evolution time for homonuclear decoupling and at the same time a compensating PIP is applied on the other side of the l3C (Fig. 11) to minimize the disturbance to the 13C that may have a transverse or longitudinal magnetization. The two simultaneous PIPs become an amplitude modulated pulse described by 2/i cos (27iAft)Ix, where f is the pulse strength of each 180°... 

As with any other homonuclear decoupling, the transverse magnetization of the 13C , for example in the evolution time, is perturbed by the decoupling pulse, resulting in an additional precession virtually around the z axis. Since the adiabatic decoupling is applied during the entire evolution time of the 13C , a non-linear frequency shift rather than a phase shift appears in the spectrum. This is termed the Bloch-Siegert (frequency) shift in the NMR literature in honour of their discovery of the phenomenon. 

Proton-proton homonuclear decoupling has been performed by the ESLG decoupling sequence [46]. Quadrature detection in coj was achieved by using the time proportional phase increment method (TPPI) [47]. During the acquisition period, two pulse phase modulation (TPPM) heteronuclear decouphng ]48] was applied (Figure 7.6). 

Selective saturation experiments were performed with the HX270 employing the homonuclear decoupling mode availcible with the instrument but substituting the usual situation by... 

The UV spectrum (/Imax 218, 237, 260,299,325, and 338 nm) of tubingensin B (380) was very similar to that of tubingensin A (379), indicating the presence of a similar carbazole framework. Comparison of the H-NMR spectrum of tubingensin B (380) with that of tubingensin A (379) indicated that these two alkaloids are structural isomers with a similar 2,3-disubstituted carbazole substructure. This was also supported with homonuclear decoupling and COSY experiments. In addition,... 

The mechanical properties of PLA rely on the stereochemistry of insertion of the lactide monomer into the PLA chain, and the process can be controlled by the catalyst used. Therefore, PLAs with desired microstructures (isotactic, heterotactic, and S3mdiotactic) can be derived from the rac- and W50-Iactide depending on the stereoselectivity of the metal catalysts in the course of the polymerization (Scheme 15) [66]. Fundamentally, two different polymerization mechanisms can be distinguished (1) chain-end control (depending on stereochemistry of the monomer), and (2) enantiomorphic site control (depending on chirality of the catalyst). In reality, stereocontrolled lactide polymerization can be achieved with a catalyst containing sterically encumbered active sites however, both chain-end and site control mechanisms may contribute to the overall stereocontrol [154]. Homonuclear decoupled NMR analysis is considered to be the most conclusive characterization technique to identify the PLA tacticity [155]. Homonuclear... 

Fig. 25 Homonuclear decoupled NMR spectrum of the methine (—C//(CH3)-) region of heterotactic PLA P = 87%) obtained from ROP of rac-lactide with [L2Mg2(p-OBn)2]2 (L = (Z)-4- [2-(dimethylamino)ethylamino](phenyl)methylene -3-methyl-l-phenyl-pyrazol-5-one) at 0 °C for 48 h (600 MHz, CDCI3) [70]...

Pig. 1. Pulse sequence for selective reverse INEPT. The time-shared homonuclear decoupling during acquisition is optional, and a variety of simplifications may be made to the sequence depending on the instrument used and on the spin system under investigation, as discussed in the text. A DANTE sequence is shown as the selective 90° carbon-13 pulse, but this may be replaced by a soft pulse or some other form of selective excitation. Phase cycling for this sequence is summarized in table 1. 

Fig. 11. Single-spin double-resonance experiment for the calibration of irradiation power. The proton line in chloroform is irradiated with the homonuclear decoupler. The strong central feature is at the irradiation frequency, and the separation of the two satellites is...

Non-selective ID experiments as well as selective ID experiments including either selective weak pulses (ID ROESY, ID TOCSY) or selective continuous radiofrequency irradiation (ID homonuclear decoupling, ID NOE). 

Fig. 3.4 One pulse experiment with selective homonuclear decoupling...

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