Alkane Reactions - Video Tutorials & Practice Problems
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concept
Common Types of Alkane Reactions
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Now when it comes to alkane reactions, realize that alkanes are the least reactive of the hydrocarbons, and in fact, they only do 2 major types of reactions. Our common types of reaction are combustion and halogenation. Now, combustion we know from Gen Chem. We say here that the simplest type of combustion reactions involve a hydrocarbon reacting with oxygen to produce carbon dioxide and water. Now, halogenation is something new. Well, this represents a substitution reaction where bromine or chlorine replaces 1 of the hydrogens on the alkane. Now here it requires heat or UV light. Here we represent UV light as HV. And what it does here is it it's to break the bond between halogens, and that halogen then attaches itself to the alkane. So if we take a look here, we have a alkane halogenation reaction. Here we have our simple alkane in the form of methane, it's reacting with X2. X here again can represent Bromine or Chlorine. So this is Cl2 or Br2. Through the use of heat or HV ultraviolet light, we split this X2 into 2 pieces. And then what happens is that one of them substitutes out this Hydrogen. So now we'd have an X here. Oops. X here. And then we'd still have an additional X hanging around, and this H just got kicked out, so they would combine together to give us HX here. Now when it comes to this, we're going to say that alkanes can be mono substituted, and that just means only 1 hydrogen is substituted, or they can be poly substituted, where more than 1 hydrogen is substituted. So pay close attention to the question being asked of you. Are they asking for a mono product, or are they asking for a poly product? If depending on what they ask, you can get different results. In this particular one, we're doing a mono halogenation. We're just replacing 1 hydrogen with a halogen. And in the end, we make an alkyl halide as a product.
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example
Alkane Reactions Example
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Here it states, what are the major products of the following halogenation reaction? Assume monosubstitution. Alright. So if we take a look at this, we know that there's a CH3 here, and a CH3 here. There is a CH 2 here, and a CH 2 here. And then here we just have another CH 2. Now you might notice that I'm trying to do some type of symmetry here. This is a pentane chain, it has symmetry in it. I'm showing that there's this red carbon on this end, and this red carbon on this end. That's telling me that they are the same. Meaning, remember in this type of reaction we're gonna substitute out 1 hydrogen for chlorine. If I put the chlorine on either end, it give me the same exact product. Both of them will be called 1 chloropentane. So let's actually show that. Right? So remember, this is just substituting a chlorine for 1 of the hydrogens. And if we were to name this, this would be 1, 2, 3, 4, 5. 1, 2, 3, 4, 5. We start numbering from the end with the substituent in the form of Chlorine. Both of these will be 1 chloropentane. Since they give the same name, they're the same molecule. So just focus only on one of them, this would just be a redundancy. Same thing with the ones in blue, if I put the chlorine on either one of them, they both would give me 2 chloropentane. So only show one of them, so this will be another major product. And then finally the one in the middle, if I put a chlorine on that one, that one's unique. Because putting one on that one would give me 3 chloropentane. So here we'd get 3 major types of products, and and that's the way you're able to determine how many possible products you can make. Add the Chlorine to different positions, and then name those molecules that you've created. If they have the same name, then they represent the same molecule. You don't need to show more than 1. Okay. Unique names equal unique products. Okay? So here we have 3 major products from the monochlorination of pentane.
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Problem
Problem
Determine the major product(s) of the following alkane reaction. (Assume monosubstitution.)