Sigmatropic migration hydrogen

The actual reported results bear out this analysis. Thus a thermal [1,3] migration is allowed to take place only antarafacially, but such a transition state would be extremely strained, and thermal [1,3] sigmatropic migrations of hydrogen are unknown." On the other hand, the photochemical pathway allows suprafacial [1,3] shifts, and a few such reactions are known, an example being " ... 

Figure 4.42 Supra (1) and antara (2) pathways of hydrogen atom migration as an example of a sigmatropic isomerization...

Figure 12.27 The 1,5 hydrogen shift occurs easily. HOMO-LUMO requires suprafacial. Sigmatropic Migration with Inversion...

We start by considering the [1,/] sigmatropic migration of a hydrogen atom within an all-cis polyolefin ... 

Fig. 10.33. Nuclear positions and for antarafacial [l,3]-sigmatropic migration of hydrogen and for suprafacial [l,3]-sigmatropic migration of mediyl with inversion (B3LYP/6-3 ++G d p) Reproduced from J. Phys. Chem. A, 106, 11533 (2002), by permission of die American Chemical Society.

Sigmatropic migrations of hydrogen are well known. They involve three pairs of electrons, so they take place by a suprafacial pathway under thermal conditions. 

Most examples of this class of reaction involve hydrogen shifts, but reactions are known in which alkyl, aryl, and other groups undergo sigmatropic migrations. ... 

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