1. Organic Naming Rules
PART ALKANES /

2. Organic Compounds Carbon Hydrogen Oxygen Nitrogen
Consist of mainly four elements
Carbon
Hydrogen
Oxygen
Nitrogen

3. Why Do We Need a Separate Set of Rules?
Examine some typical organic compounds
CH4
C2H6
Name these using typical covalent rules
Carbon tetrahydride
Dicarbon hexahydride

4. So? That wasn’t so bad, right? How about these: C4H10 C5H12
See my point?
Tetracarbon decahydride
Pentacarbon ??? hydride
Does anyone know the prefixes beyond ten?

5. C4H10 C4H10 Isomers Different Structure Same Formula
If that’s not enough, how about this one: C H
Different Structure
Same Formula C H
Definition: Isomer- chemicals that have the same formula but different structures
Formula?
Formula?
C4H10
C4H10

6. Overall Problems Memorizing too many prefixes for large numbers
Different chemicals having the same formulas
Keep in mind that thus far we’ve only dealt with TWO different elements!

7. So what to do?
Number of hydrogens is going to be the same, regardless of isomerism C H C H C H
C5H12
C5H12
C5H12

8. Solution
Since number of hydrogens don’t change with isomerism, why bother naming them?
Name the molecule simply based on number of CARBONS
We can always add prefixes or suffixes later for differentiation
The number of hydrogens will change later but for right now with only single bonds, they will always be the same.
What is the equation for C & H in an alkane? CnH2n+2

9. Name based on number of Carbons1 2 3 4 5 6 7 8 9 10
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Note the differences between this list and the covalent prefixes. Only the first four are diffferent.

10. Did that Really Help? CH4 C2H6 C8H18 C H Carbon tetrahydride becomes:
Methane
C2H6 C H
Dicarbon hexahydride becomes:
Ethane C H
C8H18
Octacarbon ???hydride becomes:
Octane

11. Branches
Straight-chain alkanes (Just C & H with single bonds) are now easy C H
C4H10 Butane
But how do we deal with branches? C H
C4H10 ????

12. Rules pt. 2 Identify the longest unbranched chain of carbons
Name it as normal
Identify the branch
Name it but give it a “–yl” suffix
Put the names of all branches first, then put name of longest chain

13. Methyl Propane Example methyl propane Branch is one long
Longest unbranched chain of carbons is three long
propane
Methyl Propane

14. Practice C H
Methyl butane H C
Ethyl pentane

15. One More Practice It doesn’t matter which way you go! Methyl Butane
(Provided you correctly pick the longest unbranched chain)
You can turn corners, go up, down, left, right, zig-zag, or do what ever you want provided you don’t double back on yourself. C
Methyl Butane

16. Methyl Hexane Be Careful Methyl Hexane C
This is your longest uninterrupted chain
Remember that molecules don’t care about left or right, top or bottom.
Hexane
Methyl Hexane

17. A Small Wrinkle Methyl Pentane Methyl PentaneC
Methyl Pentane H C
Methyl Pentane
These are different molecules, though!!!

18. So Now What?
Since two different molecules can’t have the same name, we must differentiate
If we look closely, though, the only difference between them is the position of the methyl group

19. Positioning 2- 3- So… Methyl Pentane Methyl Pentane C C
Here the methyl group is on the second carbon from the end
Here the methyl group is on the third carbon from the end
Again, the molecule on the left is 2-methyl pentane NOT 4-methyl pentane. Molecules don’t care about left or right so we start numbering from the closest side.
So…

20. Rules pt. 3 Identify the longest unbranched chain of carbons
Name it as normal
Identify the branch
Name it but give it a “–yl” suffix
Put the names of all branches first, then put name of longest chain
Put the number of the carbon the branch is on (start numbering from the closest single end)

21. Practice H C
2-methyl heptane H C
4-methyl octane H C
2-methyl hexane

22. Multiple Branches So far we’ve only had one branch
What happens when there are multple branches?
Just add a prefix to indicate the number of a particular type of branch

23. 2,2 dimethyl heptane Practice 2- methyl heptane 2- methyl
2-methyl, 2-methyl heptane
Sounds redundant
2,2 dimethyl heptane

24. More Practice 2, 6-dimethyl octane 3 ethyl-2,4-dimethyl pentane C C H
Technically you should but branches in alphabetical order but I won’t be that picky.
3 ethyl-2,4-dimethyl pentane

25. Is your arm sore yet?
Are you sick to death of writing all those carbons?
Even worse, are you sick of writing all those Hydrogens?
How about this…

26. Shorthand notation C H
Keep in mind that we have been ignoring the hydrogens for a long time.
Our names have been based entirely on the positioning of the carbons.
Each end and each “point” represents a carbon atom. The hydrogen atoms are assumed to be there.
So lets now ignore the hydrogens completely!

27. Is it that easy? H C C H

28. One More C H
Shorthand notation?
Name?
3-ethyl-2,4 dimethyl hexane

29. So is that it? Not even close!!
There are literally millions of different organic compounds.
What else can we do to make things more complicated?
Multiple bonds, rings, other atoms

30. Rings
Thus far we have dealt with chains that are straight or branched.
If hydrocarbons are long enough, one end can wrap around and link up with itself!
We call these cyclic hydrocarbons.

31. Cyclic Hydrocarbons Name the molecule as normal
Add the prefix cyclo- to the front of the name of the longest chain
Start numbering from the most “important” branch in the ring

32. Examples
Cyclohexane
Cyclooctane

33. More Examples Methyl cyclopentane 1,2 dimethyl cyclohexane
Note that a number is not needed on the first example.
Note that numbers are now needed to indicate position. It doesn’t matter, though which is 1 and which is 2
1,2 dimethyl cyclohexane

34. Try These 1 ethyl, 3 methyl cyclobutane
3 methyl, 1 propyl cylclohexane