nomenclature of organic compounds dr. m. abd-elhakeem faculty of biotechnology organic chemistry...
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Nomenclature of organic
compounds
Dr. M. Abd-Elhakeem
Faculty of Biotechnology
Organic Chemistry
Chapter 2
Name the following compounds according to IUPAC rules
Drawing structure from name
1- Start to draw the parent chain (at the end of the name).2- Add the function group in the correct position. 3- add the substitution(s).
Draw the structure of the following compounds
I- 3-nitrotolueneCH3
NO2
III- 1,2-dibromo-cyclopentane
VI- 2-hydroxy-hexanoic acid
II- 2-chloro-3-methyl-1-hexene
CH2CH3
Cl
CH3
CH3
OH
OH
O
Br
Br
V- 2,3,4-tri methyl pentane
VII- 4-chloro-2-butanone
VI- Ethanal CH3
O
CH3
O
Cl
CH3
CH3
CH3CH3
CH3
Primary, Secondary, Tertiary
A primary carbon has one other C directly bonded to it. A secondary carbon is directly bonded to two other C’s. A tertiary carbon is directly bonded to three other C’s. Multivalent atoms are 1º, 2º, or 3º by bonding to C’s. Univalent atom or group not really 1º, 2º, or 3º on its
own - ID depends on type of carbon it is bonded to.
Nomenclature of Isomers
Isomerism Isomerization It is the similarity
between organic molecules in molecular formula (number of atoms) and different in way of arrangement of atom
Biological Significance
chapter 6
Many drugs have chiral centre , with one enantiomer (form) only having the beneficial effect.
In the case of some drugs, the other enantiomer can even be harmful, e.g. thalidomide.
In the 1960’s thalidomide was given to pregnant women to reduce the effects of morning sickness.
This led to many disabilities in babies and early deaths in many cases.
H2CCH2
C
NHO O
H
N
O
O
H2CCH2
C
NH OO
H
N
O
O
L thalidomide (effective drug)
The body convert each enantiomer, so even pure L is
dangerous as it converts to D in the body.
D thalidomide (dangerous drug)
S limonene (lemons) R limonene (oranges)
CH3
HCCH2
CH3
CH3
H C CH2
H3C
Isomerism
Structural
Geometric
1. Structural Isomers
compounds have the same number of carbon and hydrogen but they are different in the way of carbon atom attachment.
Also some function groups are isomer to each other as shown in the following examples
CH3 CH2
OH O CH3
CH3
CH2 C
O
HCH3
CH3
CH3
O
2 .Stereoisomerism
The atoms are joined up in the same order, but still manage to have a different spatial arrangement.(Three dimensional arrangements). It consists of two types.
A. Geometrical IsomerismGeometric isomers: different arrangement around
a carbon-carbon double bond
Alkenes
C CH H
CH3H3C
cis-2-butene trans-2-butene
C CH
H3C
CH3
H
Ring Compounds
Cis-trans isomers possible. Example: trans-1,3-dimethylcylohexane
CH3
H
H
CH3
CH3
H
H
CH3
CH3CH3
Cis -1,2-dimethyl-cyclopropanol
Example:
CHO
O
CH
CH
C
O
OH
fumaric acid, mp 287 C essential metabolite
o
HC
CC
H
C
O
OH
O
HO
maleic acid, mp 138 C toxic irritant
o
chapter 6
Cis and Trans Isomers are called together diastereoisomers
B. Chirality
chapter 6
Mirror image isomers (Enantiomers)
It takes place when one carbon attached to four different groups.
This carbon name chiral carbon and compound name chiral compound and it has an optical activity. The groups are arranged two different ways and the two isomers are mirror images of each other.
OH
H
Cl
CH3
OH
H
Cl
CH3
Properties of IsomersDiastereomers have different physical
properties: m.p., b.p.They can be separated easily.Enantiomers differ only in reaction with
other chiral molecules and the direction in which polarized light is rotated.
Enantiomers are difficult to separate.
(R), (S) NomenclatureDifferent molecules (enantiomers)
must have different names.Usually only one enantiomer will be
biologically active.Configuration around the
chiral carbon is specified with (R) and (S).
RulesAssign a priority number to each
group attached to the chiral carbon.
Atom with highest atomic number assigned the highest priority #1.
In case of ties, look at the next atoms along the chain.
Double and triple bonds are treated like bonds to duplicate atoms.
( R )and (S)Clockwise 1-2-3 is (S) and
counterclockwise 1-2-3 is (R).Example:
CH3
H Cl
Cl H
CH3
(S)
(S)
D and L System for nomenclature
CHO
H OH
CH2OH
D-(+)-glyceraldehyde
* CHO
H OH
HO H
H OH
H OH
CH2OHD-(+)-glucose
*
COOH
H2N H
CH2CH2COOH
L-(+)-glutamic acid
* >=
Special case for chiral compounds nomenclature
Optical ActivityRotation of plane-polarized lightEnantiomers rotate light in opposite
directions, but same number of degrees.
Polarimetry
Clockwise = dextrorotatory = d or (+) Counterclockwise = levorotatory = l or (-)
Finally
Please differentiate betweenD –L and d- l (+ , -)D – L and R – S
End of Chapter 2