Question

What are the structural differences between the nine possible isomers of heptane(C7H16)?

Answer 1

They have different connectivity therefore giving them different structures. I will help you out with about 4:

n-heptane
2-methylhexane
3-methylhexane
2,2,3-trimethylbutane

I'm sure you can figure out the rest.

Answer 2

I thought that with the integer 2, it's methane and with the integer 3, its propane? But what constitutes as a structural difference? Is it the type of shape of the isomer?

Answer 3

Because I know that these are the shapes...

Answer 4

the number just designates the position of the "R" group on the longest chain.
[NOTE: R just means some alkyl group, such as methyl, ethyl, propyl, etc...]

Answer 5

The difference is because the "R" groups are on different positions. Although they all have the same molecular formula and same atoms, their properties are different. Structure is very important as it is a huge factor in how they react.

So I guess you can think of it as their "shape" but I think it's more appropriate to say their "configuration" or "arrangement"

Answer 6

What do you mean by different positions?

Answer 7

If you look at the photo with the 9 isomers, do you see how the methyl group \( (CH_3)\) is now on the the 3 position instead of the 2 position.



the methyl group is not on C2 but is on C3: \(2 \rightarrow 3\) because by IUPAC nomenclature, you name the molecule in the lowers numbering possible.

Answer 8

therefore, since the \(CH_3\) is no longer on C2, they are considered structually different.

Answer 9

I think I see, so I need to explain its structurally different by showing that the R group (still a little confused on this meaning) is on different positions on the isomers. Like in dimethylpentane there are two "R groups" on the third position.

Answer 10

Are the R groups methyl, dimethyl, ethyl, and triethyl?

Answer 11

Yes, "R" can be any one alkyl group. For dimethyl, you would have R' ( the ' means prime). I don't think you should worry about that right now, it is just used in organic chemistry to generalize a structure that can have an alkyl group that varies.

But just know that they are different because the alkyl groups are on different positions on the carbon chain.

Also, take for instance, take the last two structures! Notice that they are structurally different. They don't look the same. They have the SAME molecular formula, but they look completely different.

The longest chain for the last one on the left has 6 carbons, but the last one on the right has the longest chain composed of 4 carbons.

Does that make more sense? Remember that you look at the longest carbon chain first when naming. You have hexane, and butane. Which are different. Correct?

Answer 12

How do you know its four? Looks like six to me.

Answer 13

sorry, did I say 6, i meant \(\huge 5\)

Answer 14

What are you counting on the last one on the right?

Answer 15

By the way thank you for taking time to help me.