Coupling Constants Measurements

Modification of the ADEQUATE experiment was used by Rover and Forgo to measure single-bond and long-range couplings. The couphng-con- 

2 Residual Dipolar Couplings. - One-bond couplings are usually 

TROSY-anti-TROSY and E.COSY version of the method were described, demonstrating different arrangement of the multiplet components that allow the coupling constant measurement along different spectral dimensions. Systematic difference was observed in the coupling constants measured in H and N, ascribed to the influence of un-resolved three-bond couplings and 

Similar principle was applied for the simultaneous measurement of one-bond and two-bond couplings. The E.COSY sequence was ext- 

A somewhat similar to the above, but this time with the quadrature detection with sensitivity enhancement, was used by Ding and Gronenborn to measure different coupling involving back-bone nuclei. In one version of the method the J-evolution was introduced into 2D [ H, N]-HSQC-like spectrum by synchronising it with the chemical shift using the accordion principle. The 

Sensitivity and resolution improvements offered by the TROSY method have been utilised in two modified sequences for measuring coupling constants in proteins. Permi et proposed a 3D oc/p-HN(CO)CA-J TROSY sequence for evaluation of J(N,H ) couplings related to the torsion angle v]/. The H  

---

How are coupling constants measured from the E. COSY spectrum ... 

Comparison of the calculated and experimental values shows that the FPT-INDO method reproduces in a satisfactory way the coupling constants measured on rigid model compounds (2). The coefficients A,... 

More recently, single and double resonance techniques on both " N and N compounds are being employed for accurate shift and coupling constant measurements including relative signs. Use of enrichment with N has grown because of its favorable spectral characteristics in proton magnetic resonance studies. 

The three-state RIS model of conformer statistics is used to analyze the 16 independent dipole coupling constants measured in a proton NMR study of n-hexane in a nematic liquid crystal solvent. The orientational ordering of the n-hexane molecule is treated in the context of the modular formulation of the potential of mean torque. This formulation gives an accurate description of alkane solute orientational order and conformer probabilities in the nematic solvent. Consequently, substantially more accurate calculated diplar couplings are obtained, and this is achieved without the need to resort to unconventionally high values of the trans-gauche energy difference E(g) in the RIS model. 

The conformations of flexible chain molecules incorporated in a nematic environment are investigated. Proton-proton and carbon-carbon dipolar coupling constant measurements are attempted for 1,2-dimethoxyethane and 1,2-diphenoxyethane, in addition to 2H NMR observations of quadrupolar splittings. These conformation-dependent properties are analyzed according to the RIS scheme. Studies are further extended to a mixture of 1,2-diphenoxyethane with a nematic liquid crystal, 4,4 -azoxyanisole. 

Since the advent of NMR as a tool for conformational analysis, a number of papers have been dedicated to conformation of tetrahydro-1,3-oxazine in addition to those mentioned above. Nevertheless, conclusions based on coupling constant measurements are valid only for closely related compounds.289... 

Aimr coupling constant, measure of the splitting of lines in NMR measurements ... 

Vicinal Carbon-Proton Coupling Constants Measured Using Labeled Compounds or the Gated Technique for Natural-Abundance Compounds... 

All the substituents in the unsymmetrical 2,3,4-trisubstituted tetrahydrothiopyran 95 occupy a pseudo-equatorial site in the predominant isomer as indicated by the large vicinal coupling constants measured for the interactions between H-3, H-2 and H-4 <2000TL1321>. Limited data for the tetrahydrothiopyranium fluoroborate 96 have been reported <1995JFC(73)229>. 

N marking of the N-2 nitrogen atom, use of II, 13C, and 15N NMR spectroscopy, and coupling constants measurements 2,37N H allowed establishing the fact that the alkylation of 5-nitroindazole occurs mainly at the N-l atom [641],... 

MP4(SDTQ)/6-31 G(d,p)//ROHF/6-31 G(d) calculations by Hudson and coworkers lead to an energy difference of 2 kcal mol. Hence, the radical cation can undergo rapid pseudorotation (Figure 24), which is in line with ESR coupling constant measurements at 77 Lunell and co workers determined isotropic hyperfine coupling constants of the... 

The optimal proton position can be slightly out of the Si-O-Al plane. On the basis of the quadrupole coupling constant measurements and asymmetry values obtained from deuterium NMR experiments, Kobe et al. suggested that the... 

FruA is stereoselective and stereocenter 2 is created with the SNuclear Overhauser Effects (NOEs) observed, and the coupling constants measured, the configurations found for compound 11 were IS, 2S, 3R, and 6R. AH the substituents are equatorially positioned on the cyclohexane ring. The (2S,3R)-configurations are consistent with the usually observed diastereoselectivity of FruA In a second exploration [20], the racemic aldehyde 10 was condensed with DHAP after ketal hydrolysis of rac-14 under acidic conditions. In this case, two major isomers 12 and 13 were isolated in 35 and 29% yields after flash chromatography purification. 

---