Insensitive nuclei enhanced INEPT

INEPT (insensitive nuclei enhanced by polarization transfer) Polarization transfer pulse sequence used to record the NMR spectra of insensitive nuclei, e.g., C, with sensitivity enhancement may be used for spectral editing. 

There is another member of this family of experiments known as INEPT (Insensitive Nuclei Enhancement by Polarization Transfer), which was the forerunner of DEPT. INEPT still has its uses for obtaining spectra of really insensitive nuclei such as silicon-29 or nitrogen-15. 

In the case of the 7-hydroxy-substituted compounds 44 (Scheme 2), 54 different derivatives were investigated by 13C NMR spectroscopy and, in some cases, also by 1SN NMR spectroscopy <1995JST(335)273>. With the help of proton-coupled 13C NMR spectra, semi-selective INEPT (insensitive nuclei enhanced by polarization transfer) experiments, and heteronuclear multiple bond correlation (HMBC) two-dimensional 2D-NMR spectra, all shifts could be unequivocally assigned. While the C-7 shifts did not allow the existing tautomeric situation to be determined, a clear decision could be made by H NMR spectroscopy in this respect. The 1SN NMR spectra revealed an equilibrium between the N(4)H and N(3)H tautomeric forms, which is fast on the NMR timescale. 

INEPT insensitive nuclei enhanced by polarization transfer... 

The INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) experiment [6, 7] was the first broadband pulsed experiment for polarization transfer between heteronuclei, and has been extensively used for sensitivity enhancement and for spectral editing. For spectral editing purposes in carbon-13 NMR, more recent experiments such as DEPT, SEMUT [8] and their various enhancements [9] are usually preferable, but because of its brevity and simplicity INEPT remains the method of choice for many applications in sensitivity enhancement, and as a building block in complex pulse sequences with multiple polarization transfer steps. The potential utility of INEPT in inverse mode experiments, in which polarization is transferred from a low magnetogyric ratio nucleus to protons, was recognized quite early [10]. The principal advantage of polarization transfer over methods such as heteronuclear spin echo difference spectroscopy is the scope it offers for presaturation of the unwanted proton signals, which allows clean spec-... 

Other nuclei besides H or have been used to monitor enantiomeric discrimination with chiral lanthanide chelates. This includes the NMR spectra of chiral 2-thiabicyclo[4.3.0]nonane 2,2-dioxides (14) and 8,8-dioxides (15) with Pr(hfc)3 . The Si NMR spectrum of a-C-silylated amines and alcohols (38) in the presence of Eu(tfc)3 was used to monitor the optical purity of these compounds . A refocused-decoupled INEPT (insensitive nuclei enhanced by polarization transfer) pulse sequence was used to circumvent the long spin-lattice relaxation times of the silicon. 

More modem one-dimensional (ID) sequences such as INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) or DEPT (Distortionless Enhancement by Polarization Transfer) [6,13-15] have not been used extensively [16]. This type of experiment seems to be more powerful than the old INDOR technique. 

INEPT Insensitive nuclei enhanced by polarisation transfer 4.4.2... 

A number of papers have looked at the development of relationships between base stock composition as measured by NMR and either physi-cal/chemical properties or their performance.22 27 Most of this work has been focused on group II and III base stocks, with less or little attention paid to solvent extracted ones. These have all relied on various techniques to simplify the spectra and the assignments of peaks and make peak integration more reliable. These have many acronyms,23 for example, GASPE (gates spin echo), PCSE (proton coupled spin echo), INEPT (insensitive nuclei enhancement by polarization transfer), DEPT (distortionless enhancement by polarization), QUAT (quaternary-only carbon spectra), 2D COSY (two-dimensional homo-nuclear spectroscopy), and HETCOR (heteronuclear shift correlated spectroscopy)]. Table 4.10 provides an example of some of the chemical shift data generated26 and employed in this type of work, and Adhvaryu et al.25 were able to develop the correlations between base stock properties and carbon types in Table 4.11, whose main features correspond to intuition (e.g., the values of API and aniline points are both decreased by aromatic carbon and increased by the... 

The structures of all new compounds were determined by application of MS, H-NMR, C-NMR, DEPT, H- C HETCOR, HMQC and HMBC techniques. Structure elucidation and stereochemical assignments including absolute stereochemistry of the furanonaphthoquinone 96 involved the use of the selective INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) NMR technique and comparison of the CD (Circular Dichroism) spectra with related compounds whose absolute stereochemistry has been determined by x-ray crystallography [75]. 

A new alkaloid (7) is the first example of a Gelsemium alkaloid having an A a-methoxyindole moiety in the molecule. This alkaloid may be an early biogenetic intermediate to the A a-methoxyoxindole alkaloids and their related compounds. Full assignments of the IH- and l C-NMR spectra of A7 a-methoxy-19(Z)-anhydrovobasinediol (7) were conducted mainly by CSCM ID (decoupled selective population transfer experiment) (18) and selective INEPT (insensitive nuclei enhanced by polarization tansfer) (19) experiments. The structure was finally determined by single crystal X-ray analysis (11). 

Ag and Ag both have 7=1/2 but ° Ag is more suitable for NMR measurements . The ° Ag NMR spectra, using the INEPT (insensitive nuclei enhanced by polarization transfer) sequence [proton polarization transfer sequence between two / coupled spins /( Ag) and s( H), 7( ° ° Ag- H-imine) = 9.3 Hz (5 8.87) and 6.3 Hz (S 8.69)], have been applied to gain insight into the electronic environment and the structural and dynamic behaviour of Ag complexes in solutions . The chemical shift of the ° Ag nucleus is highly sensitive towards changes in its environment . The... 

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