Long-Range W Coupling

Examine the structure of bicyclohexane and note the spatial relationships of the various CH and CC bonds. Do all the bonds separating and Ha lie in the same plane  

Note the relationship between Ha and the other hydrogens. Long-range coupling to Ha (J 4 Hz) is observed in only one of these molecules. Which molecule do you think this is Identify the proton that is coupled to Ha. 

Plot para chemical shift (vertical axis) vs. para atomic charge (horizontal axis). Are the two properties correlated If they are, what is their relationship Does chemical shift increase ( C becomes deshielded) or decrease ( C becomes shielded) with increasing negative charge at carbon  

Draw the most important resonance contributors for nitrobenzene (include all of the contributors needed to explain for the variation in electrostatic potential, charge and chemical shift relative to benzene). Do these resonance contributors account for the different behavior of 6meta and 6paia Explain. 

Electrostatic potential map for benzonitrile shows negatively-charged regions in red and positively-charged regions (in blue). 

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A scries of a-substituted /J-(2-phenylcthcnyl)-/ -hydroxy ketones, e.g., ( )-5-hydroxy-2,2,4-trimethyl-5,7-diphenyl-6-hepten-3-one, has been investigated340. It is possible to find the most stable conformers of the diastereomeric ketones and to differentiate between them by the identification of a long-range W-coupling between the olefinic and the hydroxy proton (emphasized bonds), which can exist only in the u configuration. 

M. G. Constantino, V. Lacerda Jr., G. V. J. da Silva, L. Tasic, and R. Rittner, Principal component analysis of long-range W coupling constants of some cyclic compounds, /. Mol. Struct., 597 (2001) 129-136. 

Figure 18. A 0.2-s delayed COSY spectrum of the aliphatic region of 10 (2mg, CDCLj). Long-range "W-type" coupling of 19 and 21 axial protons to 30-CHj and coupling across the gem dimethyls from I9eq to 21 eq establish the position of oxidation at C-22. The spectrum was obtained under conditions similar to those in Figure 1, except that 32 transients were acquired for each of 128 x 512 data point spectra (17).

Only one bicyclic peroxide was obtained for each ring system and for 26 and 27 we confirmed that the bromide is cis to the peroxide linkage. In the [2,2.1]-compound this was established from its H n.m.r. spectrum by the absence of long range W-plan coupling for the CHBt proton. The cw-configuration of the [3.2.1] compound was indicated by the lH n.m.r. spectrum of the 2-bromo-3-butoxy-cyclohexanol obtained quantitatively upon reaction with butyllithium (Eq. 24), and has now been confirmed by an X-ray crystal structure determination39). 

On the methylene bridge of 9 the proton cis to the peroxide linkage (HA) appears at 8 1.87 (solvent PhH) and shows long range W-plan coupling with the 5-, and 6-endo-protons (HD), while the corresponding trans-proton (HB) exhibits no 4-bond coupling and is at 8 1.35. Compound 9a shows a similar spectrum but offset to lower field by about 0.8 ppm 28). 

Both the vicinal H,H (whether the substituent was axial or equatorial) and the long range W H,H coupling constants (whether the substituent is adjacent to the ring oxygen atom or not) in the 1,4-dioxane skeleton were used to identify several structural isomers of 2,5- and 2,6-disubstituted... 

R. T. Williamson, B. L. Marquez, W. H. Gerwick, and K. E. Kover, One- and two-dimensional gradient-selected HSQMBC NMR experiments for the efficient analysis of long-range heteronuclear coupling constants, Magn. Reson. Chem., 38 (2000) 265-273. 

Detailed examination of the NMR spectrum of securinol B (160) and its mesylate led to the conformational assignment for the alkaloid (58). The proton at C-15 in the mesylate derivative appeared as an octet (J = 9.5, 5, and 2 Hz). The small J (= 2 Hz) could be ascribed to a long-range W-type coupling between the C-15 and C-8exo protons similar to the one observed in dihydrosecurinine (Section II, E). Two possible conformations of ring C, 161 and 162, can be constructed for securinol B mesylate both of which could be expected to exhibit this... 

Barybin MV, Chisholm MH, Dalai NS, Holovics TH, Patmore NJ, Robinson R, Zipse DJ (2005) Long range electronic coupling of MM quadruple bonds (M = Mo or W) via a... 

T. Parella, 2D methods for the measurement of long-range proton-carbon coupling constants, in Multidimensional NMR Methods for the Solution State, G. A. Morris and J. W. Emsley (eds.), John Wiley Sons Ltd, Chichester, 2010, pp. 305-314. 

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