Spin-orbit coupling minimal models

The Karplus relationship makes perfect sense according to the Dirac model. When the two adjacent C—H minimal orbital overlap, with little or no spin interaction between the electrons in these orbitals. As a result, nuclear spin information is not transmitted, and Vhh = 0. Conversely, when these two bonds are parallel (a = 0°) or antiparallel (a = 180°), the coupling constant should have its greatest magnitude (Vhh = max). 

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