Question on naming alkanes...

I am doing some questions on organics, and there are alot on naming alkanes.

One of the questions is:

Name this alkane:

CH3CH2CH(CH3)CH(CH3)CH3

How would I go about doing this? What do the brackets mean?

Thank you very much.

Amrou

Reply 1

winnie the poo

It's 2,3-Dimethylpentane.

I find the easiest way is to draw it first. From that deduce the longest chain, i this case it's 5 carbons long. Branching from that there are 2 methy groups (CH3), one on the second carbon from the end, and the other on the third.

The brackets mean that that group, the one in the brackets, is attached to a carbon as oposed to a H above the carbon plane. It makes things easier to visual or else it would look something like this: CH3CH2CHCH3CHCH3CH3 which imples it is a straight chain which some missing bonds.

Hope that helps :smile:

Reply 2

Zoob

Brackets means that the CH3 is bonded to the C in the chain. It basically sticks out when u draw it. Ch3 is the methyl group.

I find the best way to tackle this is to draw out the molecule. Basically what you do is look for longest chain, ignore the sticky out bits :smile:

Then when you found the longest chain..count how at what C does that sticky out bit occur at. Start from left hand side..then Right hand side. What you are looking for is the lowest number they occur at. when u write it out, write out the position of the sticky out bits then the longest chain name.

Hope that helps :smile:

Try to name it now. For prac you just look up molecules..try to name them and then check if you are right. Good luck

EDIT: damnit too slow lol :p:

Reply 3

Renaissance_boy

Thank you very much for your help. There is just one more question. Could you possible give me advice on going about naming this molecule

CH3 CH3

CH – CH2 – C- H

CH3 C2H5

From both Ch3 to the CH on the left there are diagonal lines, and there are lines from the h to the CH3 and the C2H5 on the right.

Thank you very much.

Amrou

Reply 4

winnie the poo

I can't see how that works, 2 CH3 bonded together make a molecule in intself, ethane.

Reply 5

Eau

wesetters

I'm guessing it's this :
CH3(spaces)CH3

CH – CH2 – C- H

CH3(spaces)C2H5
2,4-dimethyl-hexane (I think, but I'm a bit rusty.

No winnie the poo is correct. There are only 5 carbons in the skeleton/main chain; methyl groups attached to second and third carbon of the chain.

Reply 6

nota bene

amrou

It isn't a trimethylpentane then? That is what I work it out to be, although it seems somewhat wrong as I get 1,1,3-trimethylpentane which obviously is ridiculous... But checking with the structure of 2,2,4-trimethylpentane it seems like it is that...WIKI

Reply 7

winnie the poo

celeritas

No winnie the poo is correct. There are only 5 carbons in the skeleton/main chain; methyl groups attached to second and third carbon of the chain.