Karplus correlation

FIGURE 3.57 The vicinal Karplus correlation. Relationship between dihedral angle (cj>) and coupling constant for vicinal protons. 

A modified Karplus correlation can be applied to vicinal coupling in alkenes. The prediction of a larger trans coupling ( = 180°) than cis coupling ( = 0°) is... 

FIGURE 3.58 The geminal Karplus correlation. 7HH for CH2 groups as a function of >H—C—H. Note the zero coupling at about 125°. 

In view of the many factors other than angle dependence that influence coupling constants, it is not surprising that there have been abuses of the Karplus correlation. Direct reading off of the angle from the magnitude of the 2J value is risky. 

There are several ways by which these four J values can be averaged pairwise one option is JX = A and /2 = 4.4 Hz, and it agrees well with the measured values, 1.4 and 5.4 Hz. In conclusion, despite the relatively small number of data points, a useful Karplus correlation was made for the three-bond 19F-13C coupling constants. 

The Karplus correlation, connecting vicinal coupling constants through the N—>Si bond in hexacoordinate complexes [1] with the corresponding dihedral angles, can now be extended also to pentacoordinate complexes on the basis of the present results (Table 3). It appears that the same Karplus-type correlation accommodates both hexa- and penta-coordinate complexes, as is depicted in Fig. 3. 

FIGURE 9.24 The Karplus correlation defines a reiationship between dihedrai angie () and coupiing... 

Karplus correlation (Section 9.9D) An empirical correlation between the magnitude of an NMR coupling constant and the dihedral angle between two coupled protons. The dihedral angles derived in this manner can provide information about molecular geometries. 

Figure 8.21 The vicinal Karplus correlation showing the relationship between dihedral angle and coupling constants for vicinal protons.

Figure 9,24 The Karplus correlation defines a relationship between dihedral angle (< ) and coupling constant for vicinal protons. (Reprinted with permission of John Wiley Sons, Inc. from Silverstein, R., and Webster, F. X., Spectrometric Identification of Organic Compounds, Sixth Edition, p. 186. Copyright 1998.)...

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