Interconversion around a “partial double bond

Interconversion Around a "Partial Double Bond" (Restricted Rotation) At room temperature, a neat sample of dimethylformamide shows two CH3 peaks because the rate of rotation around the hindered partial double bond is slow. At... 

Note that highly functionalized phosphorus ylides derived from the three-component reaction exist in solutions as a mixture of Z- and E-isomers of the corresponding zwitterionic species (56).The slow rotation about the partial double bond in (E)-3 and (Z)-3 geometrical isomers on the NMR timescale at room temperature allows an estimate of their mole ratio at equilibrium. For the zwitterionic salt of dimethyl 2(N-2-methylindole-l-yl)-3-(triphenylphosphoranylidene)butandioate (57) obtained via the above strategy from TPP, DAAD and 2-methylindole, a series of separate dynamic NMR effects at different temperatures were reported. The effects were attributed to restricted rotation around the heteroaryl-carbon and carbon-carbon single bonds and also around carbon-carbon double bond. The rotational energy barriers (AG ) for the interconversion of rotational isomers were evaluated as 55.33,49.91 and 70.16 2 kJ moU respectively. ... 

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