The Forbidden World of Chemistry

Huckel s rule, the Woodward-Hoffmann rules, and, in a broader sense, HUckel 

In short, we can say that a four-electron-four-orbital system can be bound in three different ways symbolized by the letters F, A, and N denoting forbidden , allowed , and nonaromatic fragment union, respectively. Furthermore, we note 

In addition, we can conceive of intermediate possibilities such as the ones shown below. 

We can say that isomer I is fully allowed , isomers III and IV partly forbidden , and isomer II fully forbidden . 

How is the problem of chemical stereoselection reformulated when we shift from approximate HPMO to rigorous MOVE theory First, we recall that MOVE theory has the great advantage of combining rigor with simplicity. The first attribute is due 

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