[Rutherford]

What is the name of the following alkane:
http://imageshack.us/photo/my-images/94/alk.png/
In the book it is 2,2,6,6,7-penthamethyloctane, but I would go with 3-ethyl-2,3,7,7-tetramethyloctane. I solved this so: when I find the longest row, I start from the end where the ethyl group is closest to, but how did they got 2,2,6,6,7-penthamethyloctane? What is correct?

{MOD Edit -- attach image}

[Schrödinger]

Yes, I think the book isn't right about this one. That one there on the 3rd carbon is clearly an ethyl and not a methyl

[discodermolide]

What is the name of the following alkane:
http://imageshack.us/photo/my-images/94/alk.png/
In the book it is 2,2,6,6,7-penthamethyloctane, but I would go with 3-ethyl-2,3,7,7-tetramethyloctane. I solved this so: when I find the longest row, I start from the end where the ethyl group is closest to, but how did they got 2,2,6,6,7-penthamethyloctane? What is correct?

The name is 6-ethyl-2,2,6,7-tetramethyloctane according to ChemDraw.
find the longest chain then order the substituents alphabetically.

[Rutherford]

That is similar as mine but I started from the other side to count. How to know the correct name, when the row starts to fork from 2nd carbon atom regardless from what side you start to count?

[discodermolide]

That is similar as mine but I started from the other side to count. How to know the correct name, when the row starts to fork from 2nd carbon atom regardless from what side you start to count?

Then it does not really matter, important is the longest chain.
The name I posted is not similar to yours, it has an ethyl group in it!

[Rutherford]

I didn't mean the book answer, mine answer was:

but I would go with 3-ethyl-2,3,7,7-tetramethyloctane

I don't think that it is the same compound. Do the 2 methyl group determine which side to start from?
While writting this reply I came to the next question: Does the quaternary carbon atom have advantage over the tertiary one in naming? I think that this would be a good explanation.

[discodermolide]

I didn't mean the book answer, mine answer was:

but I would go with 3-ethyl-2,3,7,7-tetramethyloctane

I don't think that it is the same compound. Do the 2 methyl group determine which side to start from?
While writting this reply I came to the next question: Does the quaternary carbon atom have advantage over the tertiary one in naming? I think that this would be a good explanation.

It is the same compound, according to ChemDraw just flipped 180°. I am not a nomenclature expert, but I believe ChemDraw is correct.
The quaternary carbon does not have any advantages.
As I said you determine the longest chain.
I think with the 6-ethyl…. you can derive the numbering sequence.

[Rutherford]

But it is a general rule that 1 compound can have only 1 correct structure formula and name. For example, 2-methylbuthane is the same as 3-methylbuthane, but according to the IUPAC nomenclature, only the first name is correct. In this problem it should be the same (only 1 name is correct).

[discodermolide]

But it is a general rule that 1 compound can have only 1 correct structure formula and name. For example, 2-methylbuthane is the same as 3-methylbuthane, but according to the IUPAC nomenclature, only the first name is correct. In this problem it should be the same (only 1 name is correct).

All you have done here is rotate the molecule by 180° and then by 90°. See the picture.
So nothing changes.
Actually there are at least two systems I know of for naming compounds, the IUPAC and the Chemical Abstracts system, both are different the last time I looked. Beilstein may be a third!

[Rutherford]

The thing about quaternary atoms that I wrote is wrong, because I found that the compound that has octane number 100 is called 2,4,4-three(?)methylpenthane.
Still, I don't understand why the name I propose isn't correct (3-ethyl-2,3,7,7-tetramethyloctane), how to know in such cases where to start from?
In a more simple case, the counting of C atoms should always start from the C atom that is nearest to another C atom that makes the row forking (English isn't my mother language so I don't know if I used the best words), but in this case there are 2 possibilities.

[discodermolide]

The thing about quaternary atoms that I wrote is wrong, because I found that the compound that has octane number 100 is called 2,4,4-three(?)methylpenthane.
Still, I don't understand why the name I propose isn't correct (3-ethyl-2,3,7,7-tetramethyloctane), how to know in such cases where to start from?
In a more simple case, the counting of C atoms should always start from the C atom that is nearest to another C atom that makes the row forking (English isn't my mother language so I don't know if I used the best words), but in this case there are 2 possibilities.

The two possibilities are the same molecule. See picture. The one on the right is your suggestion.
Have a look at the following page!
http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry

[Rutherford]

It says there: ''If there is ambiguity in the position of the substituent, depending on which end of the alkane chain is counted as "1", then numbering is chosen so that the smallest number is used. For example, (CH₃)₂CHCH₂CH₃ (isopentane) is named 2-methylbutane, not 3-methylbutane.''

3-methylbutane is incorrect, 2-methylbutane is correct. This is ok, but in my problem it isn't so easy to chose where to start from.

Why is it named 6-ethyl-2,2,6,7-tetramethyloctane and not 3-ethyl-2,3,7,7-tetramethyloctane? Is my name correct, too?

[discodermolide]

It says there: ''If there is ambiguity in the position of the substituent, depending on which end of the alkane chain is counted as "1", then numbering is chosen so that the smallest number is used. For example, (CH₃)₂CHCH₂CH₃ (isopentane) is named 2-methylbutane, not 3-methylbutane.''

3-methylbutane is incorrect, 2-methylbutane is correct. This is ok, but in my problem it isn't so easy to chose where to start from.

Why is it named 6-ethyl-2,2,6,7-tetramethyloctane and not 3-ethyl-2,3,7,7-tetramethyloctane? Is my name correct, too?

No you start from the right hand side, then all the methyl substituents have the low numbers.
6-ethyl is correct.

[Rutherford]

Do you mean that methyl substituents should have the smallest possible numbers (2,2,6,7)? This doesn't agree with 2,4,4-threemethylpenthane (2,4,4 not 2,2,4).

[discodermolide]

Do you mean that methyl substituents should have the smallest possible numbers (2,2,6,7)? This doesn't agree with 2,4,4-threemethylpenthane (2,4,4 not 2,2,4).

Quote from the link below.
The longest chain is numbered from one end to the other by Arabic numerals, the direction being so chosen as to give the lowest numbers possible to the side chains. When series of locants containing the same number of terms are compared term by term, that series is "lowest" which contains the lowest number on the occasion of the first difference. This principle is applied irrespective of the nature of the substituents.

Have a look at this page:
http://www.acdlabs.com/iupac/nomenclature/79/r79_36.htm