Why are these names incorrect?

Question

1. 2-dimethylpentane
2. 1,3-dimethylpropane
3. 3-methylbutane
4. 3,4-dimethylbutane

Answer 1

1. If both substituents are on the same number carbon, then you list the number twice: 2,2-dimethylpentane
2. Propane is a 3 carbon chain, therefore there can be no methyl groups on the ends as they become part of the primary chain. What you actually wrote was simply pentane.
3. Butane has four carbons in it. IUPAC nomenclature states that numbering begins at the end closest to a substituent, in this case a methyl group. It should be 2-methylbutane.
4. Again, you will never list a substituent as being on one of the end carbons. What you have listed is actually 3-methylpentane.

**There are many helpful references on the web regarding IUPAC nomenclature of alkanes. Just Google or Yahoo it and you'll find something good pretty quick.

Good luck!

Answer 2

Gladly, it seems that number 1 should be...

2, 2 dimethylpentane, just that another 2 was left out for the other methyl group.

Number 2, it has too many subs for a propane group which only is a 3 carbon group, thus it should be called
2-methylbutane

Number 3 should once again be a 2 methylbutane, since it can go to a lower number order, or thats how the rules of Organic chemistry for naming goes atleast, lowest number possible.

Number 4, it should be 3-methylpentane, since there is a longer carbon chain than a butane that can be formed, thus we move it up to a pentane, and let the methyl group be as a 3- since thats the lowest it can go in that position.

Best way to solve these are just to draw them out and then pick them apart with the rules. Hope it helped :+)

Answer 3

2,2-di
pentane
2-
3-methylpentane