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Organic Nomenclature:Naming Organic Molecules
What’s in a name?
Reguline Caustic
Russian Pot Ash
K2CO3Potassium Carbonate
Pearl AshOil of Tartar Mild Vegetable Alkali
Mild Vegetable AlkaliAerated Alkali
Alkahest of Reapour
Alkahest of Van HelmotFixed Vegetable Alkali
Alkali of T
artar
Cendres Gravellees
Cineres Clavellati
Fixed Alkali Salt
German Ash
Sal Alkanus Vegetablis
Sal Gentianae
Sal Guaiaci ex Ligno
Sal Juniperi
Sal TartariSalt of Tachenius
Salt of Wormwood
Tartarin
Wood Ash Alkali of Wine Lees
Glauber's Alkahest
IUPAC Rules for naming organic molecules
3
International Union of Pure and Applied Chemists
Alkanes
4
Name Molecular Formula
Prefix
Methane CH4 Meth
Ethane C2H6 Eth
Propane C3H8 Prop
Butane C4H10 But
Pentane C5H12 Pent
Hexane C6H14 Hex
Heptane C7H16 Hept
Octane C8H18 Oct
Nonane C9H20 Non
Decane C10H22 Dec
CnH2n+2
Structure of linear alkanes
5
propane butane pentane hexane
heptane octane
nonane decane
Constitutional Isomers: molecules with same molecular formula but differ in the way in which the atoms are connected to each other
6
Physical properties of constiutional
isomers
7
Isomers
8
n # of isomers 1 1 2 1 3 1 4 2 5 3 6 5 7 9 8 18 9 35 10 75 15 4,347 25 36,797,588
The more carbons in a molecule, the more possible ways to put them together.
Naming more complex molecules
9
C6H14
hexane
Naming more complex molecules
10
Step 1: identify the longest continuous linear chain: this will be the root name: this is the root name
1
2
3
4
5
6 longest chain = 6 (hexane)
1 2 3
4
51
2 34
51
2 34
incorrectcorrectlongest chain = 5 (pentane) longest chain = 5 (pentane)
12
3
4
12 3
4
longest chain = 4 (butane) longest chain = 4 (butane)
Naming more complex molecules
11
Step 2: identify all functional group (the groups not part of the “main chain”)
1 2 3
4
51
2 34
5
main chain: pentane main chain: pentane
12
3
4
12 3
4
main chain: butane main chain: butane
CH3
CH3
CH3CH3 CH3
CH3
Alkyl groups: fragments of alkanes
12
methane methyl
CH4 CH3
empty space (point where it attaches to something else)H C
H
H
HC
H
H
H
More generally...
13
H C C C
H
H
H
H
H
H
H C C
H
H
H
H
CC
H
H
H H
H
C
H
C
H
H
H
ethyl propyl butylC2H5 C3H7 C4H9
CnH2n+1
Naming more complex molecules
14
1 2 3
4
51
2 34
5
main chain: pentanegroup: methyl (x1)
main chain: pentanegroup: methyl (x1)
12
3
4
12 3
4
main chain: butanegroup: methyl (x2)
main chain: butanegroup: methyl (x2)
CH3
CH3
CH3CH3 CH3
CH3
Naming more complex molecules
15
1 2 3
4
5
1
2 34
5
Step 3: position of the group denoted by number of carbon of main chain that it is attached to.
2-methylpentane
3-methylpentane
position of group
name of group
main chain
5 4 3
2
1
4-methylpentane
incorrect: start numbering from the end that gives groups the lowest number
Multiple groups
16
12
3
4
12 3
4
2,2-dimethylbutane 2,3-dimethylbutane
there are 2 methyl groups
group prefixdi=2tri=3
tetra=4penta=5hexa=6
Common Problems
17
1
23
45
67
1 2 3 45
6
4-ethylheptanenot
3-propylhexane
Be careful to choose the longest chain!
Numbering and priorities
18
Always start numbering to give the lowest number for the first substituent:
2,3-dimethylpentanenot 3,4-dimethylpentane
3,5,7-trimethyldecanenot 3,6,8-trimethyldecane
19
3/6
3-ethyl-6-methyloctanenot 3-methyl-6-ethyloctane
ignore “di-”, “tri-” etc. for
alphabetical ordering
5-ethyl-3-methyloctanenot 4-ethyl-6-methyloctanenot 3-methyl-5-ethyloctane
4-ethyl-2,8-dimethylnonanenot 2,8-dimethyl-4-ethylnonane
if same #s obtained in both directions, first
group listed gets lower number
groups listed in alphabetical
order
Groups within groups
20
What happens when the alkyl group isn’t a straight chain?
“isopropyl” (common name)
“t-butyl” or “tert-butyl” (common name)
“s-butyl” or “sec-butyl” (common name)
21
Treat branched side chains as groups with groups on them. Start numbering chain from point of attachment to main chain.
12
34
56
7
12
1-methylethyl group
4-(1-methylethyl)heptane
4-(1,1-dimethylethyl)heptane
5-(1-methylpropyl)nonane
Beyond alkanes
22
Alkyl halides: compounds containing F, Cl, Br, I
Br
1-bromobutaneCl
2-chloropentane
Fl
4-(1-fluoroethyl)heptaneI
I
1,1-diiodopropane
Alcohols
23
OH
1-propanolor
propan-1-ol
OH
ethanol
name of alkane--> replace “e” with “ol”
OH
2-propanolor
propan-2-ol
HOOH
1,4-dihydoxybutane
