Push-pull allenes

Alternatively, the substituents A and B may stabilise a cationic centre on one side and the substituents C and D an anionic centre on the other 2.102. Alkenes having donor substituents at one end and acceptors at the other are called push-pull alkenes, and the barriers to rotation are indeed lowered,137 with the enamine system of the alkene 2.107 having a barrier of 66 kJ mol-1 (16 kcal mol-1).138 More subtly, the substituents in the allene 2.108 enable the phenyl and the methyl groups to exchange places rapidly, with coalescence of... 

Saalfrank and his co-workers have described syntheses and properties of further types of push-pull substituted allenes. ... 

FIGURE 1-7 Push/Pull Processes for Ethan Allen Supply Chain for Customized Furniture... 

All processes in the customer order and manufacturing cycle at Ethan Allen are classified as pull processes because they are initiated by customer order arrival. The company, however, does not place component orders in response to a customer order. Inventory is replenished in anticipation of customer demand. All processes in the procurement cycle for Ethan Allen are thus classified as push processes, because they are in response to a forecast. 

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