Hi, Could anyone help me with this questions, question 8 part b.
when the answer says ' sextet' , I understand that it refers there is carbon next door attaching 5 proton. But as far as I can see, there isn't any such carbon.
Also, I am a bit confused about N+1 rule because the next door carbon could refer to either left or right? So, which side is it?
Thanks in advance!
Hi!
Since carbon forms a maximum of four bonds (as it is tetravalent), a single carbon actually can't bond with five protons. The N+1 rule refers to the carbons on both sides of the carbon you're thinking of.
For instance, if we consider the diagram on the left, the second carbon from the left is a CH2 group, bonded to a CH3 group on the left and a CH2 group on the right. An arrangement like this will produce a sextet in the H-NMR spectrum - there is a carbon atom attached to two carbon atoms with five protons in total that are directly attached, so using the n+1 rule, there is a sextet.
The other sextet from the diagram on the left, I think, comes from the carbon attached to the hydroxyl group. Note that it is also attached to a CH3 and a CH2 group (five identical hydrogens on either side), so a sextet is present.
When we do the N+1 rule, it's also worth noting that a hydroxyl group will show a singlet (it is not attached to an atom directly attached to any other hydrogens).
Also, when using the N+1 rule on adjacent hydrogens, if an -OH group is present on the adjacent carbon, you don't add this. For instance, if we consider the third carbon on the left diagram, we see that it is attached to a CH2 group, and a carbon attached to a H and an OH. In this case, we look only at the hydrogens directly attached to adjacent carbons - so the third carbon in this diagram is attached to a carbon with 2 hydrogens directly attached and another carbon with only one hydrogen attached (3 in total). This produces a quartet by the N+1 rule.
Similar logic is applied to the structural formula on the right.
I hope this helps! If you have any more questions, don't hesitate to ask.