drawing isomers

[Nomvalt]

Draw the possible structural isomers for hexane. State its sytematic name and semi-structural formula.

When I drew these I got a lot of different isomers:

hexane
2-methylpentane
3-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
1,2-dimethylbutane
1,4-dimethylbutane
1,2,3-trimethylpropane
1,1,2-trimethylpropane
1,2,2-trimethylpropane

...and well, I stopped after this as I was just bewildered by the number of isomers I had to draw and I was getting sick of doing it! I just made a quick google search and found out that there are in fact only 5 isomers for hexane, so what did I do wrong? Which ones above are the same? I don't know what the answers are as there are no answers and I don't have the worked solutions.

[kenhung123]

1,2 dimethyl butane is same as 2 methyl pentane
1,2,3 trimethyl propane is same as 3 methyl pentane
1,1,2 trimethyl propane is same as 2 methyl pentane
1,2,2 is same as 2 methyl pentane

[kenhung123]

Yea, these are annoying. Basically you can't draw anything that simply looks different. You got to do that first and then keep twisting the molecule around to ensure that it cannot be the same as another isomer. So its really trial and error.

[andy456]

I got:
Hexane
2 methylpentane
3 methylpentane
2,3 dimethylbutane

What's the other one???

[Nomvalt]

2,2 dimethyl butane is same as 3 methyl pentane
1,2,3 trimethyl propane is same as 3 methyl pentane
1,1,2 trimethyl propane is same as 2 methyl pentane
1,2,2 is same as 2 methyl pentane

Okay, I'm worried now. I can't seem to see how they are the same.

[kenhung123]

Well I did the first one. I hope its clear.

[Mao]

In general:

Methyl groups cannot be at the start or end of the chain (otherwise they'll be part of the 'backbone'), in other words, 1-methyl (and similarly, the last methyl) are redundant.

Ethyl groups cannot be at the first two or last two carbons of the chain. In other words, 1-ethyl, 2-ethyl (and similarly, the last ethyls) are redundant.

Isomers of hexane are:

Hexane
2-methylpentane
3-methylpentane
2,2-dimethylbutane
2,3-dimethylbutane

[Nomvalt]

Methyl groups cannot be at the start or end of the chain (otherwise they'll be part of the 'backbone'), in other words, 1-methyl (and similarly, the last methyl) are redundant.

I see what you're saying here.

Ethyl groups cannot be at the first two or last two carbons of the chain. In other words, 1-ethyl, 2-ethyl (and similarly, the last ethyls) are redundant.

Why?

[Nomvalt]

Ethyl groups cannot be at the first two or last two carbons of the chain. In other words, 1-ethyl, 2-ethyl (and similarly, the last ethyls) are redundant.

Why?
[/quote]

Nevermind, I see now!