Intro to Addition Reactions - Video Tutorials & Practice Problems
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concept
Addition Reactions
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Now we can say here that alkenes and alkynes undergo addition reactions. Now what exactly is an addition reaction? Well, this is the addition of atoms to pi bonds, which results in double or triple bonds breaking. So double or triple bond breakage. Here we're going to say that PI bonds are broken, and new sigma bonds are formed. Here we're going to say there are 3 major types of addition reactions, and they are Halogenation, Hydrogenation, and Hydrohalogenation. So here we take a look at additional reactions, we have here halogenation and hydro hydrogenation. Halogenation just means that we're adding halogens to our Pi bonds. If we take a look here, we have our alkene, we have a carbon here and a carbon here, remember carbon must make 4 bonds. What happens is we break one of these pi bonds, and we use that bond to help us attach these 2 halogens to my used to be alkene. In the process we make what's called a dihalide. In hydrogenation, we're adding hydrogens to our PI bond. So here, these 2 hydrogens get added, we still have these other hydrogens attached, so they're still there. We're more focused on what's our new overall compound. So adding hydrogens here through hydrogenation creates what? An alkane. Then if we go to hydrohalogenation, we put this a bit different because we're not adding the same two groups to the double bond. Here we have our alkene and we're using HX. So here we have hydrogen and a halogen, the halogen here is bromine or chlorine. What happens is that we have the Hydrogen and Halogen adding to create an Alkyl halide. Later on, we'll learn specific rules to tell us which double bonded carbon gets the hydrogen and which one gets the halogen. But for right now just realize that hydro halogenation adds a hydrogen, which is the hydro part, and a halogen, which is the halogen part, to create an alkyl halide. Now, here we're going to say, we have 1 mole of reagent needed for every Pi bond. So if we had a triple bond, we'd need 2 moles of the reagent. Alkene only has 1 pi bond, so we only need 1 mole. Now, remember, a double bond is composed of 1 sigma bond and 1 pi bond. A triple bond is consistent of 1 sigma bond and 2 pi bonds. The Sigma bond is always going to be there. It's just the number of Pi bonds that are increasing. Right? So just remember, we have these three types of additional reactions that are pretty common amongst alkene species and alkyne species.
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example
Intro To Addition Reactions Example
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Which of the following represents an addition reaction? So remember, at this point, we're talking about addition reaction in respect to alkenes and alkynes. We're adding things to these alkenes and alkynes by sacrificing their Pi bonds. If we take a look at the first one, we have a PI bond here, but it's not of an alkene or an alkyne, and it's still there at the end, so this would not be our type of addition reaction. Next we have an alcohol, and we're using some type of acid and heat, and it actually creates an alkene. Remember, addition reactions were getting rid of the PI bond to add things to our structure. The answer is c, because in c, what do we have? We have an alkene, we're adding hydrochloric acid to it, We see that an H got added here, and a chlorine got added to the other alkene carbon. This represents hydrohalogenation. This would be our type of additional reaction we've covered so far. Alright. So here our final answer will be option c.
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Problem
Problem
How many moles of reagent are needed for the addition of the following alkyne?
A
2 moles
B
3 moles
C
1 mole
D
4 moles
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