4-Iodo-l-butene

The polarity and partial charges of l-iodo-2-butene are dictated by the electronegativity of oxygen versus the electronegativity of carbon. Additionally, delocalization through the double bond extends the chain of partial charges. Therefore, the partial charges and polarity are as represented below, and a nucleophile is most likely to react at either of the specified carbon atoms via an SN2 or an SN2 mechanism. 

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