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- Solutions 63

Draw structures for all constitutional isomers with the molecular formula C_{4}H_{8} that have:

(a) Only single bonds

Hey guys. So, in this problem we're going to go ahead and calculate all of the different constitutional isomers for the compound C4H8, okay? So let's go ahead and do this, there's a quick and easy way to figure out if we have any rings or double bonds here, okay? So guys, what is that way? IHD, right? using index of hydrogen deficiency, we know the formula is 2 n plus 2 minus H divided by 2 where the n is the number of carbons and H is the number of hydrogens, okay? So what do we have? 2 times 4 plus 2 minus 8, all divided by 2, right? 2 times 4 that's 8, plus 2 that's 10, right? So, 10 minus 8, that's 2 divided by 2 giving us 1 IHD, okay? So I'm actually going to go ahead and just draw out a straight chain of carbons and the hydrogens explicitly and then we'll do it in bond line, okay? Guys, but wait a minute, we know that we have an IHD of 1, which means that we're missing two hydrogens, what do we know can give us that? either a ring or a double bond, right? So I'm actually going to go ahead and draw a double bond right here, okay? And the rest of these need to be filled with the number of hydrogens, right? Let's go ahead and make sure all of our carbons have the right number of bonds, right? We have four bonds on this carbon, perfect, four bonds on this carbon, four on this and four on this, right? So we're fine, okay? And I'm actually going to go ahead and draw this a bond line now, we know that looks just like this, right? Okay, so now guys, what about another thing? Well, we can actually just go ahead and move our double bond, right? So we can have something looks like this with a double bond there, if I move it over here, if I do something like this, right? Guys, these two are exactly the same thing, all I did is really just rotate it, right? So we don't have to draw in this one, okay? Because it's the exact same thing but now we don't, we can't just use double bonds only, right? We know that we can have a ring, okay? So guys, our ring, I'm actually going to go ahead and draw just like this, right? Just a square, right? And we know that on each of these we've got two hydrogens, right? We know that we've got two on each of these because we need to our carbon needs to have four bonds, so guys, this is actually another one of our constitutional isomers, but wait a minute, our IHD in a ring doesn't depend on the size of the ring, right? And we know that we've got four carbons, guys what's the smallest number of carbons we can need that we could use to make a ring? three, right? So we can actually have a three carbon ring right here with another carbon coming off right there, right? And let's take a look and make sure we have the right number of carbons, right? We've got two, four, five eight, right? So guys these two are also valid structures, okay? Guys, these are, these are all of our constitutional isomers that we have. Alright guys, I hope that helps, let me know if you have any questions, let's move on.