Leaving Groups Good, Bad and Ugly

Good leaving groups RHal and epoxides can be further activated with Lewis acids 

Finally, HOH and ROH can leave protonated alcohols or ethers as leaving groups, hut neither the OH group (from alcohols) nor the OR group (from ethers, except for epoxides, see above) can leave. Remember, the conjugate acid of water is the hydronium ion, a strong acid (pKa = -1.7) 

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