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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
1 Meth
2 Eth
3 Prop
4 But
5 Penta
6 Hexa
7 Hept
8 Oct
9 Non
10 Deca
==>
Molecular formula Name
CH4 Methane
C2H6 Ethane
C3H8 Propane
C4H10 Butane
C5H12 Pentane
C6H14 Hexane
C7H16 Heptane
C8H18 Octane
C9H20 Nonane
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

n-heptane
2-methylhexane
3-methylhexane
2,2-dimethyl pentane
3,3-dimethyl pentane
2,3-dimethyl pentane
2,2,3-trimethyl 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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