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level 2 -naming alkenes
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Level 1-Alkanes Level 2-Alkenes Level 3 Alkynes Level 4 Benzenes Level 5 Dienes Level 6 Trienes Level 7 Cyclic Compounds
Level 1-Naming Alkanes
I found over the years that just giving the rules is overwhelming for naming organic compounds. If
you just want the rules click here===> RULES.
I am going to take you through all the isomers of methane through octane.
Alkanes- Are saturated (all single bonds) hydrocarbons (hydrogen and carbon only).
The rule for naming is they all end with "-ane".
The general formula is CnH2n+2, n is the number of carbons is used to determine the number of
hydrogen atoms. Example n=5, so H=(2(5) +2)=12
C5H12
# Carbons prefix
Molecular formula
Name
1
Meth
CH4
Methane
2
Eth
C2H6
Ethane
3
Prop
C3H8
Propane
4
But
C4H10
Butane
5
Penta
C5H12
Pentane
6
Hexa
C6H14
Hexane
7
Hept
C7H16
Heptane
8
Oct
C8H18
Octane
9
Non
C9H20
Nonane
10
Deca
C10H22
Decane
==>
Homologous Series- Did you notice that as you go down from CH4 to C2H6 (and so on) the next member is different by 1 carbon and 2
hydrogen?
Now molecular formulas have limitations. You never really know how the molecule is constructed. So let's look at the structural formulas and name each.
The first 3 alkanes have no isomers (they can only be drawn 1 way). Makes for a good multiple choice question.
Methane
Ethane
Propane
Naming Compounds- Ignore all the hydrogen's. We only worry about carbon atoms.
Isomers of Butane C4H10
Rule #1-Name the longest continuous chain of carbon atoms, and end it with -ane.
This is butane, but we call
it
n-butane
n stands for normal
Rule #2- Remaining side chains will be given the ending -yl. They are placed before the longest chain when naming.
The longest chain is 3 carbons, so
"propane". There is one carbon
left. We call this "methyl".
Therefore,
methyl propane
Isomers of Pentane C5H12
n-pentane
methyl
butane
Rule #3- Multiple side chains will use prefixes 2 is di-, 3 is tri-, 4 is tetra- and so on.
Longest chain is 3, so propane
2 separate, one carbon side chains
is dimethyl
dimethyl propane
Isomers of Hexane C6H14
n-hexane
methyl pentane
methyl pentane
WAIT....these are different structures with the same names...
Rule #4 When necessary use the lowest number to give the location of each side chain. You may have to number the longest chain from
the right side to find the lowest number. (NOTE numbers and letters are separated by a hyphen)
2-methyl
pentane
3-methyl
pentane
2,2-dimethyl
butane
Did you notice we had to number from the right? If we named from the left it would be 3,3-dimethyl butane.
2+2 vs. 3+3 always use the lowest numbers.
2,3-dimethyl
butane
Isomers of Heptane C7H16
nheptane
2methylhexane
3methylhexane
2,2-dimethyl pentane
3,3-dimethyl pentane
2,3-dimethyl pentane
2,2,3trimethyl
butane
Again, each side chain gets a number. Since we have 3, one carbon side chains, it is called "trimethyl". You better have 3#'s when you have the tri prefix.
ethyl pentane
This has 1(2-carbon) side chain. It is NOT dimethyl. Dimethyl is 2(1-carbon) side chains. This is an "ethyl" group.
Notice I did not use a number. If was moved one carbon to the left...
3-methyl hexane
The longest chain becomes hexane.
Isomers of Octane C8H18
n-octane
2-methyl heptane
3-methyl
heptane
4-methyl
heptane
2,2-dimethyl hexane
2,3-dimethyl hexane
2,4-dimethyl hexane
2,5-dimethyl hexane
3,3-dimethyl hexane
3,4-dimethyl hexane
ethyl hexane
(no number needed)
2,2,3-trimethyl
pentane
2,2,4-trimethyl pentane
2,3,3-trimethyl pentane
(number it from the right
side)
2,3,4-trimethyl
pentane
Rule #5- When there are 2 different side chains name them in alphabetical order using the carbon prefix (meth, eth..).
ethyl-2-methyl pentane
(ethyl does not need a #,
it can only go on carbon
3)
ethyl-3-methyl pentane
tetramethyl butane
(no # needed 4 carbons
must occupy 2,2,3,3)
Level 1-Alkanes Level 2-Alkenes Level 3 Alkynes Level 4 Benzenes Level 5 Dienes Level 6 Trienes Level 7 Cyclic Compounds
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