Rearrangement position shift

Plandier rearrangement position shift Stevens rearrangement vanadate -Wagner-Meerwein -... 

F ritsch-Buttenberg-Wiechell — homoallyl — migration nitroso groups rearrangement position shift retroallyl rearrangement ring — santonin —... 

Polysacdiarides s. Disacdiarides Polysolfides s. Trisulfides Position shift (s. a. Migration, Rearrangement)... 

Wiechell rearrangement homoallyl rearrangement migration position shift retroallyl rearrangement snatoin —... 

BUTENE. As shown in Figure 38, a group attached to C-1 can migrate from position 1 to 3 (1,3 shift) to produce an isomer. If it is a methyl group, we recover a 1-butene. If it is a hydrogen atom, 2-butene is obtained. A third possible product is the cyclopropane derivative. The photochemical rearrangement of 1-butene was studied extensively both experimentally [88]... 

Examine the transition state for the hydride shift. Calculate the barrier from the more stable initial carbocation. Is the process more facile than typical thermal rearrangements of neutral molecules (.05 to. 08 au or approximately 30-50 kcal/mol) Is the barrier so small (<.02 au or approximately 12 kcal/mol) that it would be impossible to stop the rearrangement even at very low temperature Where is the positive charge in the transition state Examine atomic charges and the electrostatic potential map to tell. Is the name hydride shift appropriate If not, propose a more appropriate name. 

The electron impact positive ion spectrum of l,2,5-oxadiazolo[3,4-/]quinoline IV-oxide 46 shows the loss of N2O2 from the molecular ion, a process that must be followed by a substantial rearrangement to enable the observed loss of propyne-nitrile. This remarkable result apparently arises through a series of H-atom shifts which relocate the dehydroaromatic moiety in the heteroring (890MS465). 

Abstraction of a hydride ion from a tertiary carbon is easier than from a secondary, which is easier than from a primary position. The formed car-bocation can rearrange through a methide-hydride shift similar to what has been explained in catalytic reforming. This isomerization reaction is responsible for a high ratio of branched isomers in the products. 

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