Systematic name?

[barydos]

Hey guys,

Just wondering, what would you call this molecule?

Which side would you label as your number 1 carbon?  The one closer to the one with 2 methyl groups or the one with only 1 methyl group?

[Conic]

I think it's 2,2,3 trimethyl butane numbered from left to right.

[barydos]

In a more complex molecule, would we have to indicate which carbon atom has the double methyl group like... by saying trimethyl, we're not specifying which one has the 2 or which one has the 1. Is it every necessary to specify?

Suppose we had a chlorine atom on the atom on the right, what would it be called?

(By the way thanks haha)

[nubs]

In a more complex molecule, would we have to indicate which carbon atom has the double methyl group like... by saying trimethyl, we're not specifying which one has the 2 or which one has the 1. Is it every necessary to specify?

Conic said 2,2,3- trimethylbutane
Since '2' is repeated twice, that means there are two methyl groups on that carbon

I believe that 2,3,3-trimethylbutane would not exist however, so if you were to number the carbons from right to left instead of left to right, you would be wrong in doing so. I assume this would be because the second carbon from the left has more methyl groups attached to it so it would be given priority.

If a chlorine atom were attached to the fourth carbon, then the name would be 1- chloro 2,3,3-trimethylbutane I think

The reason the carbon with the chlorine atom is numbered as the 'first' carbon along the parent chain is because different functional groups and side chains are grouped together in alphabetical order, so the chlorine will be given priority over the methyl groups because 'c' comes before 'm'
The 'tri' in 'trimethyl...' is ignored however. So if we were to have 'dimethyl...' instead, the chlorine will still be given priority, because we ignore the prefix (di-) when determining the alphabetical order
As a result, in this case, we have '2,3,3-...' instead of '2,2,3...', because the two methyl groups are on the third carbon along the parent chain

[barydos]

Thanks so much nubs, and to Conic as well.
Everything is so much clearer now

Edit: Actually one last question just out of curiosity, you know how 3 methyls -> trimethyl, what about 4 of them?

[jgoudie]

1 - nothing (mono if anything)
2 - di
3 - tri
4 - tetra
5 - penta
6 - hexa
7 - hepta
8 - octa
9 - nona
10 - deca

Seriously doubt you would go over 4 in vce though.

[Chazef]

what I don't understand is why you need the prefix di, tri etc. when the amount of numbers preceding the functional group already indicate how many there are. If I have 2,3,3 trimethyl.... then I already know there'll be three methyl groups without requiring the tri- prefix to tell me so. So I was wondering, is there ever a situation where the prefix is necessary in determining the structure of the molecule?

Also, say I have heptane and on the middle Carbon, I place an ethyl group, then put a chloro functional group on the second carbon in the ethyl group, how would I name that molecule. Would it be something like 3-(2-chloroethyl) heptane?

Thanks in advance for any responses

[Limista]

what I don't understand is why you need the prefix di, tri etc. when the amount of numbers preceding the functional group already indicate how many there are. If I have 2,3,3 trimethyl.... then I already know there'll be three methyl groups without requiring the tri- prefix to tell me so. So I was wondering, is there ever a situation where the prefix is necessary in determining the structure of the molecule?

This is the convention. You have to put the numbers AND the prefix - these two factors are always necessary.

Also, say I have heptane and on the middle Carbon, I place an ethyl group, then put a chloro functional group on the second carbon in the ethyl group, how would I name that molecule. Would it be something like 3-(2-chloroethyl) heptane?

I think it would be just 4 chloroethylheptane, but I think someone should confirm.

[nubs]

Also, say I have heptane and on the middle Carbon, I place an ethyl group, then put a chloro functional group on the second carbon in the ethyl group, how would I name that molecule. Would it be something like 3-(2-chloroethyl) heptane?

EDIT: Sorry, misread what you wrote

It would be 4-(2-chloroethyl)heptane, not 3-(2-chloroethyl)heptane
You said place the ethyl group on the middle carbon, which is the fourth, not the third
Don't recall needing to know that for VCE chemistry but yeah the course might have changed a bit

[Limista]

Since, alphabetically, 'chloro' comes before 'ethyl', the chlorine will be given priority. This means we begin numbering the parent chain that is closer to the chlorine end.

Since the chlorine is on the second carbon and the ethyl is on the fourth carbon, we have 2-chloro-4-ethylheptane
Even when you name it, make sure the groups and side chains are put in alphabetical order

EDIT: Sorry, misread what you wrote

Just a question - in an ethyl group, there are 2 carbons right? So wouldn't numbering it as 2-chloro be the same as 1-chloro?

[nubs]

I deleted that part of my message because I read the question wrong, I've changed it to what I think is the correct answer thoughhhh

But yeah, for chloroethane it would be the same as you said. 1-chloroethane is the same as 2-chloroethane
But once it's attached to something like heptane in the form of 'chloroethyl', the chlorine could be on either the carbon of the ethyl group that is closer to the parent chain (the carbon bonded to the parent chain), or the carbon further away.
To distinguish between the two, the carbon on the ethyl group bonded to the parent chain would be numbered '1', and the second carbon would be numbered '2'

So 1-chloroethyl would be -CHClCH3
2-chlroethyl would be -CH2CH2Cl

[Limista]

^ all clear now 

[barydos]

I might as well ask another relevant question I just came across.

For carboxylic acids, is the carbon in COOH the "leading" carbon (i.e. labelled number 1)? I've always had the impression it's the trailing one.

[saba.ay]

I might as well ask another relevant question I just came across.

For carboxylic acids, is the carbon in COOH the "leading" carbon (i.e. labelled number 1)? I've always had the impression it's the trailing one.

Yes, it's always the Carbon which has the carboxyl functional group which gets precedence and gets the smallest number possible.  unless you have an amine/amino (NH2) group present. If the compound has both the amine and the carboxyl functional group, then you try and give the smallest number to the carbon which has the amine functional group on it, because from what I understand, NH2 gets precedence over COOH. Having said that, I haven't come across any compounds, other than amino acids, which have both the amine and carboxyl functional group.

[barydos]

Great, thanks a lot riversong.