Nomenclature: URGENT HELP!!!!!!

I don't understand the horizontal line...I mean, why is there a CH2 next to a CH3? Does that not mean five carbon bonds are being made rather than 4? And why is one carbon not bonded to any hydrogen atoms?
Thanks...

Reply 1

goam

9

hm not quite sure what you're asking... but for your last question are you talking about the centre carbon?- carbon atoms don't necessarily have to be attached to any hydrogens, they just need 4 bonds

Reply 2

CounTolstoy

OP

14

@GDL/LPC student
I'm sorry to bother you again, but if you have a moment to spare could you please help me out with this question? Thanks in advance.

Reply 3

CounTolstoy

OP

14

Original post by goam

hm not quite sure what you're asking... but for your last question are you talking about the centre carbon?- carbon atoms don't necessarily have to be attached to any hydrogens, they just need 4 bonds

Apologies for not making my question clear.
In the last diagram, there is: CH3-C-CH2-CH3
Okay, you have answered part of my question since I thought one carbon could only bond with 4 hydrogens. My other question is: how do I know how many hydrogens it bonds with? For example, how do I know it's CH2 and not just CH? Thank you for your time.

Reply 4

GDL/LPC student

1

Original post by CounTolstoy

@GDL/LPC student
I'm sorry to bother you again, but if you have a moment to spare could you please help me out with this question? Thanks in advance.

Sure, I have a biochemistry degree, so I should know haha.So, you need to count the bonds. The carbon with no H's has 4 bonds. The CH2 carbon is bonded to two carbons, so has two left for hydrogen. The CH3 carbon has one bond already taken, so there's three left for hydrogen.
Remember, count the bonds that are shown (the lines) and figure out how many C-H bonds it will take to bring it up to 4.

(edited 7 years ago)

Reply 5

mercuryman

20

Q: Why is 1 carbon not bonded to any hydrogens?

Ans: Valency. Each carbon atom can only bond to a maximum of 4 Atoms. There's no room for hydrogens.

The horizontal line is the carbon chain. The vertical line is the branches that stem off the carbon chain.

This molecule is quite complex to start off with, but essentially the longest out of the horizontal/vertical chain is the carbon back bone of the molecule .
In this case the horizontal line is the largest, hence the molecule is a butane compound.

The shortest is the vertical line that has two methyl groups attached on the 2nd Butane carbon.

Hence, you'd call it
.. 2-dimethylbutane

(edited 7 years ago)

Reply 6

goam

9

Original post by CounTolstoy

Apologies for not making my question clear.
In the last diagram, there is: CH3-C-CH2-CH3
Okay, you have answered part of my question since I thought one carbon could only bond with 4 hydrogens. My other question is: how do I know how many hydrogens it bonds with? For example, how do I know it's CH2 and not just CH? Thank you for your time.

Are you referring to being asked to draw hydrocarbons? If so, the name you're given e.g 2,2-dimethylbutane will tell you the positions and number of carbons. So you draw out all the carbons then attach hydrogens so that each carbon has 4 bonds. Sorry if this isn't very clear, I'm bad at explaining stuff!

Reply 7

aerofanatic

7

Original post by CounTolstoy

Apologies for not making my question clear.
In the last diagram, there is: CH3-C-CH2-CH3
Okay, you have answered part of my question since I thought one carbon could only bond with 4 hydrogens. My other question is: how do I know how many hydrogens it bonds with? For example, how do I know it's CH2 and not just CH? Thank you for your time.

Most nomenclature you will work with at A-level will be with stable molecules. 2,2-dimethylbutane is stable. For this organic compound to be stable, all carbons must have four bonds to other entities (e.g. atoms, chemical groups, etc.)

The 'butane' part of the name suggests to start with a four-carbon long chain.
The 2,2-dimethyl part suggests that on the second carbon, we have two methyl groups attached, i.e. -CH3 group.
The rest of the 'free' carbon bonds need to be attached to hydrogen atoms.

Reply 8

CounTolstoy

OP

14

Original post by GDL/LPC student

Sure, I have a biochemistry degree, so I should know haha.So, you need to count the bonds. The carbon with no H's has 4 bonds. The CH2 carbon is bonded to two carbons, so has two left for hydrogen. The CH3 carbon has one bond already taken, so there's three left for hydrogen.
Remember, count the bonds that are shown (the lines) and figure out how many C-H bonds it will take to bring it up to 4.