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Organic Nomenclature:
Naming Organic Molecules
Aerated Alkali
What’s in a name?
Mild Vegeta
ble Alkali
Tartarin
Glauber's Alka
hest
t
o
lm
e
H
n
a
V
f
o
t
s
e
Alkah
Fixed Vegetable Alkali R
ussian Pot Ash
es
e
l
l
e
v
a
r
G
s
e
Cendr
lkali
A
e
l
b
a
t
r
e
g
e
Mild V
ta
r
a
T
f
o
K2CO3
li
a
k
Al
Sal Juniperi
Alkahest of Reapour
Potassium Carbonate
Salt of Tachenius
Sal Ta
Salt o
rtari
dA
xe
Sal Gentia
nae
Reguline Caustic
sh
A
d
Woo
Fi
Alkali of Wine Lees
German Ash
Oil of Tartar Pearl Ash
alt
li S
lka
f Wor
o
n
g
mwo
Li
i
t
a
l
x
l
e
e
v
od
a
i
l
c
C
s
a
e
i
r
e
a
n
i
u
C
Sal Alkanus Vegetablis
Sal G
IUPAC Rules for naming
organic molecules
International Union of Pure and Applied
Chemists
3
Name
Alkanes
CnH2n+2
Prefix
Methane
Molecular
Formula
CH4
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
Meth
4
Structure of linear alkanes
propane
butane
heptane
nonane
pentane
hexane
octane
decane
5
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
The more carbons in a
molecule, the more
possible ways to put
them together.
n
1
2
3
4
5
6
7
8
9
10
15
25
# of isomers
1
1
1
2
3
5
9
18
35
75
4,347
36,797,588
8
Naming more complex molecules
hexane
C6H14
9
Naming more complex molecules
Step 1: identify the longest continuous linear chain: this will be the
root name: this is the root name
2
1
1
4
6
3
2
longest chain = 6 (hexane)
5
2
4
3
5
2
4
1
longest chain = 5 (pentane)
1
3
3
5
correct
longest chain = 5 (pentane)
1
4
longest chain = 4 (butane)
2
2
3
1
3
4
incorrect
4
longest chain = 4 (butane)
10
Naming more complex molecules
Step 2: identify all functional group (the groups not part of the “main
chain”)
CH3
2
1
2
4
3
5
main chain: pentane
4
3
1
5
CH3
main chain: pentane
CH3
1
2
3
1
4
CH3
CH3
main chain: butane
2
3
4
CH3
main chain: butane
11
Alkyl groups: fragments of alkanes
H
H
C
H
H
H
C
H
H
methane
methyl
CH4
CH3
empty space (point where it
attaches to something else)
12
More generally...
H
H
H
C
C
H
H
ethyl
C2H5
H
H
H
H
C
C
C
H
H
H
propyl
C3H7
CnH2n+1
H
H
H
H
H
C
C
C
C
H
H
H
H
butyl
C4H9
13
Naming more complex molecules
CH3
2
1
2
4
3
5
main chain: pentane
group: methyl (x1)
4
3
1
5
CH3
main chain: pentane
group: methyl (x1)
CH3
1
2
3
1
4
CH3
CH3
main chain: butane
group: methyl (x2)
2
3
4
CH3
main chain: butane
group: methyl (x2)
14
Naming more complex molecules
Step 3: position of the group denoted by number of carbon of main
chain that it is attached to.
4
2
1
3
5
2-methylpentane
position
of group
name of
group
2
1
3
main
chain
5
4
2
3
1
4-methylpentane
incorrect: start numbering from
the end that gives groups the
lowest number
4
5
3-methylpentane
15
Multiple groups
1
2
3
1
4
2,2-dimethylbutane
2
3
4
2,3-dimethylbutane
there are 2 methyl groups
group prefix
di=2
tri=3
tetra=4
penta=5
hexa=6
16
Common Problems
Be careful to choose the longest chain!
1
2
1
3
3
2
4
4
5
5
6
6
4-ethylheptane
not
3-propylhexane
7
17
Numbering and priorities
Always start numbering to give the lowest number for the first
substituent:
2,3-dimethylpentane
not 3,4-dimethylpentane
3,5,7-trimethyldecane
not 3,6,8-trimethyldecane
18
5-ethyl-3-methyloctane
not 4-ethyl-6-methyloctane
not 3-methyl-5-ethyloctane
3/6
groups listed in
alphabetical
order
4-ethyl-2,8-dimethylnonane
not 2,8-dimethyl-4-ethylnonane
ignore “di-”, “tri-”
etc. for
alphabetical
ordering
3-ethyl-6-methyloctane
not 3-methyl-6-ethyloctane
if same #s
obtained in both
directions, first
group listed gets
lower number
19
Groups within groups
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)
20
Treat branched side chains as groups with groups on them. Start
numbering chain from point of attachment to main chain.
2
1-methylethyl group
1
4-(1-methylethyl)heptane
1
2
3
4
5
6
7
4-(1,1-dimethylethyl)heptane
5-(1-methylpropyl)nonane
21
Beyond alkanes
Alkyl halides: compounds containing F, Cl, Br, I
Br
1-bromobutane
I
I
1,1-diiodopropane
Cl
2-chloropentane
Fl
4-(1-fluoroethyl)heptane
22
Alcohols
name of alkane--> replace “e” with “ol”
OH
OH
ethanol
OH
1-propanol
or
propan-1-ol
2-propanol
or
propan-2-ol
OH
HO
1,4-dihydoxybutane
23