Hydrogen atom 1,7-shifts thermally

Ene reaction (Hydro-allyl addition)-A reaction of an allylic compound with an olefin which resembles both a cycloaddition and a [1, 5]-sigmatropic shift of hydrogen. In this reaction an alkene having an allylic hydrogen atom reacts thermally with a dienophile (enophile) C = C, C = 0, N = N, N = 0, C = S... 

Alkynes containing methylene (—CHi—) functionalities a to the triple bond readily undergo thermal C-H activation under conditions necessary to initiate reaction with group VIII metal carbonyls (54). The allenyl clusters obtained isomerize thermally via a 1,2-hydrogen atom shift to afford the thermodynamically more favorable 1,3-dimetalloallyl clusters (Table 1) (49,55). A similar chemistry has been recognized for osmium clusters, albeit under more severe conditions. 

So it is the number of electrons and not the number of atoms which determines the selection rule. Therefore, the selection rules for hydrogen migration in thermal sigmatropic shifts can be summarized as follows as given in the table ... 

We now consider hydrogen transfer reactions between the excited impurity molecules and the neighboring host molecules in crystals. Prass et al. [1988, 1989] and Steidl et al. [1988] studied the abstraction of an hydrogen atom from fluorene by an impurity acridine molecule in its lowest triplet state. The fluorene molecule is oriented in a favorable position for the transfer (Figure 6.18). The radical pair thus formed is deactivated by the reverse transition. H atom abstraction by acridine molecules competes with the radiative deactivation (phosphorescence) of the 3T state, and the temperature dependence of transfer rate constant is inferred from the kinetic measurements in the range 33-143 K. Below 72 K, k(T) is described by Eq. (2.30) with n = 1, while at T>70K the Arrhenius law holds with the apparent activation energy of 0.33 kcal/mol (120 cm-1). The value of a corresponds to the thermal excitation of the symmetric vibration that is observed in the Raman spectrum of the host crystal. The shift in its frequency after deuteration shows that this is a libration i.e., the tunneling is enhanced by hindered molecular rotation in crystal. 

Since the shift of a hydrogen atom is not possible with the methoxy-(phenyl) carbene ligand, it can only dimerize in reactions with bases and in thermal liberations (75). 

With an appropriate choice of B the compensation is effective for all atomic velocities. As the velocity of the thermal beam of hydrogen atoms at 300 K is not well known, the magnetic field will be used to measure precisely the velocity distribution, and so the second order Doppler shift. 

This thermal ring opening favors the fomtation of ( )-o-quinodimethanes (587) over that of (Z)-dienes (588) which, when the substituent R bears a hydrogen atom (R = XH), undergo a 1,S-H shift. For this and other reasons, the ( )-configuration of terminally substituted o-quinodimethanes is relevant for their use in Diels-Alder reactions. ... 

Thermal or photochemical activation of the complexes results in the formation of siloxycarbenes 13 via diradicals 12. Carbenes 13 lie in a very shallow minimum and are stabilized by a [1.2]H shift, if an a-hydrogen atom is available, or by [l,2]silyl migration Vinyloxysilanol 8 or formylsilanol 11 are the final oxydation products in argon matrices. 

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