O
Organic chemistry
i h i
Nomenclature of Organic compounds
Bridge course
Nomenclature of organic
compounds
Th are two
There
t systems
t
off naming
i
1 Trivial system
1.
2. IUPAC system
y
Trivial system:
When a few organic
g
compounds
p
were known,,
they were named on the basis of their history
or source.
source
Eg: HCOOH –Formic acid (red ants)
CH3COOH‐Aceticacid
COOH A ti id (acetum‐vinegar)
( t
i
)
IUPAC system:
(International Union of Pure and Applied Chemistry)
By using this system one can name any B
i thi t complex organic compound easily.
The name assigned to an organic compound on the basis of latest IUPAC p
rules is known as systematic name.
W iti IUPAC name off a compound
Writing
d
y The IUPAC name of the compound
p
built from 4 parts
y Prefix
y word root
y primary suffix
y secondary suffix
Prefix
y It denotes the substituent group if present in the organic compound
p
g
p
Substituent group
prefix
‐F
Fluoro
l
‐Cl
Cl
chloro
‐Br
Bromo
substituent
prefix
‐I Iodo
‐NO2 Nitro
NO2 Nitro
‐CH3 Methyl
‐C2H5 Ethyl
‐C3H7 Propyl 3 7
py
Word root
y It indicates the number of carbon atoms in
the longest possible chain.
N off carbon
No.
b atoms
1
2
3
word
d root
meth‐
eth‐
prop‐
No.of carbon atoms
Word root
4
but‐
5
6
7
8
9
10
pent‐
hex‐
hept‐
p
0ct‐
non‐
dec‐
Primary Suffix
yIt denote the nature of carbon to
carbon bond
compounds.
yane:
b d
bond
yene:
bond
yyne:
bond
in
the
organic
S
Secondary
d
suffix
ffi
It represents the functional group if
present in an organic molecule and is
attached
h d to the
h primary
i
suffix
ffi while
hil
writing the IUPAC name.
Class of functional secondaryy
compounds group suffix
Alcohol ‐OH ‐ol
Aldehydes ‐CHO ‐al
Ketones >C=O ‐one
Carboxylic acids COOH oic acid
Carboxylic acids ‐COOH ‐oic acid
Amines ‐NH2 ‐amine
E t COOR t
Esters ‐COOR ‐0ate
Writing
W
ii
IUPAC name off an
aliphatic compound
IUPAC= prefix (es)+word root + primary IUPAC
fi ( )
d t i
suffix +secondary suffix
Eg:
g
H3C
3
Word root
root-:: prop
CH
2
CH3
H2
C
1
OH
Prefix -: methyl
Pi
Primary
suffix-:
ffi -ane
Secondary suffix-: -ol
IUPAC name- 2-Methyl-1-propanol
(terminal ‘e’ of the p-suffix is dropped if the sec-suffix begins
with
ith a,e,i,o,u)
i
)
IUPAC rules for naming organic
compounds
1.Longest chain rule:
Select the longest continuous chain of carbon atoms
known as “parent” chain
1
2 3
4
5
3 4
5
6
CH3-CH-CH2-CH2-CH3 CH3-CH-CH2-CH2-CH3
|
|
CH2-CH
CH3
CH2-CH
CH3
2
1
2-Ethylpentane
2
Ethylpentane
33-Methyl
Methyl hexane
(wrong)
(correct)
2.Lowest number rule
The carbon chain selected is numbered from the end
nearest to the side chain or substituent so as to give the
lowest number to the carbon carrying the side chain.
1
2 3
4
4
3
2
1
CH3-CH-CH2-CH3 CH3-CH-CH2-CH3
|
|
CH3
C
CH3
C
2‐Methylbutane
( correct))
3‐Methylbutane
(
(wrong)
)
Lowest sum rule:
Where there are more than one substituent, numbering
of the chain is done in such a way that the sum of the
numbers assigned to the substituents is minimum.
“The
e te
term Locant
oca t iss used to de
denote
ote tthe
e number
u be
indicating the substituent attached”.
CH3
CH3
CH3 CH3
1 2| 3 4| 5
5 4|
3 2| 1
CH3-C-CH2-CH-CH3 CH3-CH-CH2-CH-CH3
|
|
CH3
CH3
2,2,4‐trimethylpentane
2,2,4
trimethylpentane
2,4,4‐trimethylpentane
2,4,4
trimethylpentane
Set of locants= 2+2+4=8
set of locants=2+4+4=10
(correct)
(wrong)
3 Arrangement of Prefixes
3. Arrangement of Prefixes
If more than one group is attached to the carbon chain, these groups should be arranged alphabetically. When two or more identical substituents are present prefixes like di, tri, tetra, etc. are used. However these prefixes are not considered for alphabetical order.
1 2 3 4 5 6 1 2 3
CH3-CH-CH2-CH-CH2-CH3
CH3
CH CH2 CH CH2 CH3
|
|
4 5 6
CH3-CH-CH2-CH-CH2-CH3
CH3
CH CH2 CH CH2 CH3
|
|
CH3 CH2 CH3 CH2
|
CH3
|
CH3
2-Methyl-4-ethylhexane
4-Ethyl-2-methylhexane
(wrong) (right)
y If two different groups are located at the equivalent
positions, the
h numbering
b
should
h ld be
b done
d
in such
h a
way that alkyl group which comes first in the
alphabetical
p
order g
gets the lowest p
position.
1
2
3
4
5
6
CH3-CH
C
C 2-CH-CH-CH
C C C 2-CH
C 3
|
|
C2H5 CH3
3-Ethyl-4-methylhexane
4: Lowest Number to the Functional
Group
p
y In case there is a functional group in a molecule, the parent chain is numbered such that the f
functional group gets the lowest number, even if ti
l t th l
t b if the lowest number rule is violeted. CH3
H3C
1
C
2
CH3
CH3
H2
C
3
H
C
4
CH3
5
OH
2,2-Dimethylpentan-4-ol
2,2
Dimethylpentan 4 ol
wrong
H3C
5
C
4
CH3
H2
C
3
H
C
2
CH3
1
OH
4,4-Dimethylpentan-2-ol
,
e y pe
o
Right
5 Presence of Identical groups
If an organic molecule has more than one functional group, prefixes like di, tri, tetra are used before the fi lik di i d b f h suffix indicating the functional group. However, the ‘e’ of the corresponding alkane is retained
e of the corresponding alkane is retained.
4
H3C
3
CH
OH
2H
C
1
CH2
OH OH
Butane-1,2,3-triol
2
1
H2C
CN
H2C
CN
4
3
Butane-1,4-dinitrile
Nomenclature of unsaturated hydro carbons
a )
H 3C
4
H2
C
C
H2
CH2
H3C
1
1
3
But-1-ene
c)
b)
C
C
CH3
2
3
4
But-2-yne
5
4
3
2
1
H3C
C
H
C
H
C
H
CH2
Penta-1,3-diene
IUPAC nomenclature of poly
functional compound
In
case
of
polyfunctional
compounds one of the functional
group chosen as the principal
group and
d the
th compound
d is
i named
d
on that basis.
The order of decreasing priority
for functional groups
g p
Sulphonicacid>carboxylic acid>ester>acid chloride
>amide> nitrile> aldehyde>
y
ketone>
alcohol>amine>doublebond>triple
bond>ether>other substituents (X>NO2>R)
OHC
H2
C
H2
C
H2
C
COOH
4
3
2
1
principal functional group
substituent group
4-Formylbutanoicacid
The IUPAC name of an alicyclic compounds
is prefixed with “cyclo”.
NO2
1
3
2
2
a))
b)
c)
1
Cyclohexane
y
3
3-Nitrocyclohexene
y
1-Methyl-3-propylcyclohexane
Nomenclature of Aromatic
compounds
NH2
6
5
a)
O2N
Cl
1
2
4
3
1
b)
NO2
CH3
6
2
5
3
4
C2H5
1-Chloro-2,4-dinitrobenzene
4-Ethyl-2-methylaniline
IUPAC names of organic compounds by bond line notation
b b d li i
b
a
But-2-ene
2,3-Dimethylbuta-1,3-diene
d
c
2,2-Dimethylbutane
3,3-Diethylpentane
THANK YOU
BRIDGE COURSE‐2012