One of the reaction mechanisms in A Level Chemistry Syllabus is Electrophilic Addition of Alkenes.<br /><br />We need to be able to describe this mechanism in detail using curvy arrows.<br /><br />Let's use the bromination of ethene as an example:<br /><br />electrophilic addition example using bromination of ethene<br /><br />Electrophilic Addition Step 1 - Attack on electrophile to generate carbocation intermediate<br />Electron rich alkene will use the pi bond to attack the partially positively charged bromine atom which is closer to it.<br /><br />A carbon-bromine bond is formed.<br /><br />The other carbon which loses the electron will become positively charged, hence the name carbocation.<br /><br />Bromide ion, Br- is also formed in the first step.<br /><br />Take note that the first step is the slow step or rate determining step.<br /><br />electrophilic addition step one - attack on electrophile to form carbocation<br /><br />Electrophilic Addition Step 2 - Attack on carbocation by Br- to form product<br />The Br- formed will attack the carbocation and form the second carbon-bromine bond to form the product 1,2-dibromoethane.<br /><br />electrophilic addition step two - bromide attack carbocation to form product<br /><br />It's important to note that even though we are adding 2 bromine to alkene, they are added to the alkene differently:<br /><br />a. First Br is added as an electrophile in the first step (highlighted yellow in the screenshot)<br /><br />b. Second Br is added as a nucleophile in the second step (highlighted blue in the screenshot)<br /><br />Check out this video lesson for a step-by-step tutorial to learn how to draw the mechanism via curly arrows!<br /><br />Topic: Alkenes (Hydrocarbons), Organic Chemistry, JC, H2, A Level Chemistry, Singapore<br /><br />You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/electrophilic-addition-mechanism-for-alkenes<br /><br />Do check out the following for more video lessons:<br />Organic Chemistry Videos at https://chemistryguru.com.sg/a-level-organic-chemistry-video-lessons<br />A Level Chemistry Videos at https://chemistryguru.com.sg/a-level-chemistry-video-lessons<br /><br />If you are looking for H2 Chemistry Tuition, do consider taking up my classes at Bishan. More info at https://chemistryguru.com.sg/
