Using Curved Arrows in Polar Reaction Mechanisms

O A hydrogen atom on the electrophile HBr is attacked by tt electrons from the nucleophilic double bond, forming a new C-H bond. This leaves the other carbon atom with a + charge and a vacant p orbital. Simultaneously, two electrons from the H-Br bond move onto bromine, giving bromide anion. 

Problem 5.7 Reaction of HBr with 2-methylpropene yields 2-bromo-2-methyipropane. What is the structure of the carbocation formed during the reaction Show the mechanism of the reaction. 

6 Using Curved Arrows in Polar Reaction Mechanisms 

Test your knowledge of Key Ideas by using resources in ThomsonNOW or by answering end-of-chapter problems marked with A. 

It takes practice to use curved arrows properly in reaction mechanisms, but there are a few rules and a few common patterns you should look for that will help you become more proficient. 

RULE 1 Electrons move from a nucleophilic source (Nu to an electrophilic sink (E). The nucleophilic source must have an electron pair available, usually either in a lone pair or a multiple bond. For example  

Electrons usually flow from one of these nucleophiles  

The electrophilic sink must be able to accept an electron pair, usually because it has either a positively charged atom or a positively polarized atom in a functional group. For example  

If the nucleophile is neutral, the atom that gives away an electron pair acquires a positive charge. For example  

The electrophilic sink must be able to accept an electron pair, usually 

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Rules for using curved arrows in polar reaction mechanisms (Section 5.6). 

Using Curved Arrows In Polar Reaction Mechanisms... 

USING CURVED ARROWS IN POLAR REACTION MECHANISMS... 

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