HMBC spectroscopy

Other two-dimensional techniques, such as COSY (122), DEPT (123), HOHAHA, soHd state (124) etc. give varying degrees of success when apphed to the stmcture-property relationship of cellulose triesters. The recent appHcation of multiple-bond correlation (HMBC) spectroscopy for... 

Heteronuclear (X, H) Multiple Bond Correlation (HMBC) spectroscopy is a modified... 

The photochemical reaction of tertiary amines with C6o can be used to synthesize alkaloid-C6o derivatives [269], Irradiation of alkaloids bearing a tertiary amino group such as tazettine, gramine, scandine, or 10-hydroxyscandine with C6o led to the isolation of alkaloid-C6o adducts. Use of tazettine and gramine in the reaction yielded the expected [6,6] adduct. In addition to the pyrrolidinofullerene 94a-b, a new type of monoadduct 95a-b with a bis-[6,6] closed structure characterized by UV-vis, FT-IR, II-NMR, 13C-NMR, II- II-COSY, ROESY, HMQC, and HMBC spectroscopy was obtained from the reaction with scandine 93a and its 10-hydroxy derivative 93b (Scheme 38). 

Interestingly, even small Se, C coupling constants via two to four bonds (13.7-1.7 Hz) could be identified benzoselenadiazoles by ID C-detected Se HMBC spectroscopy. ... 

HMBC spectroscopy has been also very useful to observe the differences between amine -NMe2 carbosilane dendrimers and dendrons and the corresponding cationic -NMe2R derivatives (R = H, Me), detecting a similar higher frequency for the N resonances of cationic groups. ... 

Other two-dimensional techniques, such as correlation spectroscopy (COSY) (118), DEPT (119), Homonnclear Hartmann-Hahn (HOHAHA), sohd state (120), etc, give var5nng degrees of snccess when applied to the structure-property relationship of cellnlose triesters. The recent application of H—multiple-bond correlation (HMBC) spectroscopy for the imambiguous assignment of cellulose mixed esters has successfully demonstrated the utility of NMR for the structiu-e elucidation of complex cellnlose esters (121). It is this unique abihty to provide detailed information on intermolecular interactions of cellulose esters in coatings (115) or in polymeric blends that continues to put NMR spectroscopy well ahead of other analytical techniqnes. 

Because of the complexity of the polyether antibiotics tittle progress has been made in stmcture determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early stmcture elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and H (192) and nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for stmcture determinations. Eor example, heteronuclear multiple bond connectivity (hmbc) and homonuclear Hartmann-Hahn spectroscopy were used to solve the stmcture of portimicin (14) (193). East atom bombardment mass spectrometry was used in solving the stmctures of maduramicin alpha and co-factors (58). 

The structure of this compoimd 63a was determined by H and C NMR spectroscopy. The H NMR spectrum shows singlets at 1.45 ppm for the methyl protons, and at 4.17 and 6.30 ppm for the hydroxylic and ethylenic protons. The addition regioselectivity in the formation of 63a was established by H- C HMBC 2D-NMR, which shows the C5-C4-C3-Me linkages. The ethylenic proton correlates only with three carbon atoms Ce, C5, and C3. The methyl protons correlate with C3 and with the ethylenic carbon C4, consistent with the neighboring C3-C4 connection. The NOESY spectrum shows... 

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. 

In order to assign the chemical shifts of the carbon atoms of the conjugated diene system of each CLA isomer, it was necessary to conduct INADEQUATE, HMBC (heteronuclear multiple bond correlation) and two-dimensional 1H-13C correlation spectroscopy (COSY) techniques on the carbon signals of the diene system of the ,Z-isomers. The results of these experiments for the CLA isomers are summarized in Table 13. 

HMBC Heteronuclear multiple-bond correlation spectroscopy To elucidate structure of organic molecules To establish long-range (i.e., multibond) heteronuclear coupling... 

In many cases, the analytical tasks are simply to detect and quantify a specific known analyte. Examples include the detection and quantification of commonly used buffer components (e.g., Tris, acetate, citrate, MES, propylene glycol, etc.). These simple tasks can readily be accomplished by using a standard one-dimensional NMR method. In other situations, the analytical tasks may involve identifying unknown compounds. This type of task usually requires homonuclear and heteronuclear two-dimensional NMR experiments, such as COSY, TOCSY, NOESY, HSQC, HMBC, etc. The identification of unknown molecules may also require additional information from other analytical methods, such as mass spectrometry, UV-Vis spectroscopy, and IR spectroscopy.14... 

The use of NMR, MS, IR spectroscopy, and to a lesser extent x-ray crystallography has become routine since the mid-1980s. Particularly, the use of sophisticated NMR techniques such as NOE, COSY, HETCOR, HMBC etc., has become indispensable for structure elucidation, and has provided much insight into the field of reaction mechanisms. 

Hadden, C.E., Martin, G.E., and Krishnamurthy, V.V., Constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation spectroscopy CIGAR-HMBC, Magn. Reson. Chem., 38, 143, 2000. 

H and C NMR spectroscopies were systematically used to elucidate the structure of C-glycosylflavonoids the assignment of signals was based upon various experiments, HMBC, HMQC, COSY, etc., as shown in the following examples ... 

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