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Video Solution: From among the 18 constitutional isomers of C 8H18,...

Problem

From among the 18 constitutional isomers of C 8H18, write structural formulas, and give the IUPAC names for those that are named as derivatives of

(a) Heptane

Video Transcript

Alright. So, for Part A of this question, we are going to be drawing and naming the constitutional isomers that are heptane derivatives for C8H18, so remember that C8H18 is just going to be a regular alkane, right? So, C8H18 will look something like this, we have 1, 2, 3, 4, 5, 6, 78 carbons but now we need ones that are heptane. So, for heptane we now are going to have one less carbon in our carbon chain. So, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 7, right? So this structure is the only one that we can use to draw in our constitutional isomers and it turns out there's actually going to be 3 different constitutional isomers that have heptane as the root for C8H18. So, how are we going to do this? Well, what we can do is we now need to add in one more carbon, so it's all about which position are we going to add it to, so let's say in the first one we add it to this carbon right here. So, carbon 2, but carbon 2 would be the same as carbon 6 over here, okay? For the next one what do you think we should do to make it different? we're going to add it to carbon 3 now. So, here is our last carbon, but now which other position would be similar to add this methyl group? it was 2 and 6 in the first one here is going to be 3 and 5, right? Because it would be the same if we have the methyl group right here, so I told you there's one more. So, do you guys know which one it is? where are we adding that methyl group? Well, right in the middle, right? Right here at position 4 and now all we need to do is name this, which is pretty easy because we're just going to use this number right here and we're going to say, the first is going to be to methyl, right? So let's write that in 2 with 2 methyl and now it's heptane, right? So, heptane, what would be the next one? Well, go ahead and try and do this one on your own, the same thing of the first one is that we just changed that 2 for a 3, so this is going to be 3 methyl heptane, right? It would be incorrect to call this 5 methyl heptane because we know why your substituent is the lowest number, so that's why there's only one isomer that's possible here and at the last one all we, you guys know, all we need to do is write 4-methyl heptane, okay? And we're done, so these are the three constitutional isomers that have heptane in them for C8H18. Alright, so hopefully that made sense.

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