Download nomenclature and stereoisomerism

Organic nomenclature and
isomerism
Nomenclature
Nomenclature review
3,5-dimethylheptane
Trans-but-2-ene
trichloromethane
Pentan-2-ol
2-bromo-3-chloropentane
H H
Br C C C C
H H H
H
H
4-bromobut-1-ene
2-methylpropan-2-ol
5-chlorohex-5-en-3-ol
3,4,9-trimethyldecane
H
H
Cl
H
H
C
H
C
C
C
H
C
H
H
H
H
chlorodimethylpropane
H
(E)-5-bromopent-2-ene
H H
H
H
C
H
C
C
H
H
C
C
C
H
H
H H
H
cyclohexane
Lesson objectives
• Understand and be able to work with IUPAC
nomenclature extended to more complex
compounds including cyclic, aromatic and
heterocyclic compounds.
• Be able to draw and build structures which show
geometrical (E-Z) isomerism
• Recognise asymmetrical carbon atoms and
understand that they give rise to optical isomers
Success criteria
• Name and draw the structure of different groups of
organic compounds
• Give reason why geometrical isomers exist.
• Draw molecules that show geometrical isomers
• Identify asymmetrical carbon atoms
• Draw optical isomers.
Keywords
•
•
•
•
•
•
•
•
•
•
•
•
Aromatic
Ortho
Para
Meta
Heterocyclic
Stereoisomers
Geometrical isomers
Optical isomers
Asymmetrical/ chiral carbon
Superimpose
Non-superimpose
Enantiomer
Aromatic Hydrocarbons
Aromatic Compounds
Aromatic compounds contain benzene ring.
Benzene has:
C6H6
• 6 C atoms and 6 H atoms.
• Two possible Lewis structures.
Naming of Aromatic Compounds
Aromatic compounds are named:
• With benzene as the parent chain.
• Name of substituent comes in front of the “benzene”.
• CH3-methyl
Cl-chloro
• CH2CH3-ethyl
Br-bromo
• NO2 –nitro
F-fluoro
CH3
methylbenzene
Cl
Chlorobenzene
CH2-CH3
ethylbenzene
Nomenclature of Benzene
•Di-substituted benzene. ID the
“parent”. You can use “benzene”, or
combine a substituent with benzene
as the parent.
•Then use the lowest numbering
system or ortho, meta, para
designations:
1-bromo-3-chloro benzene, or
3-chloro-bromobenzene, or
meta-chloro-bromobenzene
Naming of Aromatic Compounds
If we have three or more substituents:
- Start numbering from a special name (if we have).
- If we do not have, number them to get the smallest set of numbers.
- List them by alphabetical order.
Naming of Aromatic Compounds
Aryl group: When we remove a H atom from an arene (Ar-).
Phenyl C6H5-
1
Nomenclature of Benzene
•Common Names (you must learn these):
toluene
benzoic acid
phenol
benzaldehyde
benzyl alcohol
acetophenone
aniline
benzyl bromide
Activity-6 minutes
Heterocyclic compounds
• Organic compounds that contain a ring
structure containing in addition to
carbon, such as sulfur, oxygen and
nitrogen as the heteroatom
Nomenclature of heterocyclic
compounds
It is based on:
• Types of heteroatom (O, N, S, e.t.c)
• Ring size
• Nature of the ring
Naming heterocyclic compounds
• IUPAC name = Prefix + suffix
• Prefix- from the atom present
• Suffix= from the size of the ring
Atom
Prefix
O
S
N
oxa
thia
aza
Priority decreases
• Examples
H
N
• This ring contains (N)
Prefix is aza
• The ring is 3-membered and fully saturated
suffix is iridine
• By combining the prefix and suffix, two vowels
ended up together (azairidine), therefore the vowel on
the end of the first part should be dropped. This gives
the correct name: Aziridine
Heterocyclic Chemistry
Oxirane
oxole
oxetane
Most common heterocyclic
molecules
Pyrrole
Furan
Pyrrolidine/ tetrahydropyrrole
Thiophene
Pyridine
Isomerism
• The existence of two or more molecules
with the same molecular formula but
different structures or arrangement of
atoms in space.
27
ISOMERISM
STRUCTURAL ISOMERS
= molecules with the same
molecular formula but
different structural
formulas.
Chain
Functiona
l group
Position
STEREOISOMERS
= isomers with the same
structural formula but
different spatial
arrangements
geometrical
Optical
Types of isomers
Pentane
2-methylbutane
2,2-dimethylpropane
Chain isomers
1-propanol
2-propanol
Position isomers
Propanal
Propanone
Functional group isomers
Cis-but-2-ene
Trans-but-2-ene
Geometrical (Cis-Trans)
isomers
Geometrical isomers
• Watch video
Geometrical isomers
Which of the molecules will show geometrical isomer?
B
Name the two geometrical isomers.
Trans-but-2-ene
cis-but-2-ene
Explain why they show geometrical isomerism.
The presence of a double bond with a restricted rotation
Each of the carbon of the double bond is attached to two
different group.
H
H
C
H
E-pent-2-ene
Z-pent-2-ene
H
Chiral and Achiral Molecules
• Although everything has a mirror image, mirror images may
or may not be superimposable.
• Some molecules are like hands. Left and right hands are
mirror images, but they are not identical, or superimposable.
36
• Optical isomers
mirror images.
are
non-superimposable
• Condition for optical isomerism
• Involves a tetrahedral sp3 atom i.e carbon atom
joined to four different groups. Carbons of
this type are called ‘chiral./ asymmetric carbon
• No plane of symmetry.
H
CH3
C
CH2
CH3
OH
Chiral Centre
2-Butanol
CH3
HO
H
C
CH3
H
C OH
CH2
CH2
CH3
CH3
Stereoisomers whose molecules are nonsuperimposable mirror images of one another are
called enantiomers
CO2H
H H
CO2H
H3C C C CO2H
OH OH
Cl C2H5
H3C C C CH3
HO
O
Cl Cl
CO2H
H F
CH3
H3C C C CH3
OH OH
Cl C2H5
C6H5 C C CH3
HO
O
O
Cl
C6H5
Cl
Naming Enantiomers
The R,S system of nomenclature
Rank the groups (atoms) bonded to the chirality
center
Orient the lowest priority (4) away from you
Clockwise = R configuration
Counterclockwise = S configuration
e.g
1. Rank the groups bonded to the asymmetric carbon
1
4
2
3
2. If the group (or atom) with the lowest priority is
bonded by hatched wedge, do not reverse, if not
reverse
• If two atoms on a stereogenic center are the same, assign
priority based on the atomic number of the atoms bonded to
these atoms. One atom of higher atomic number determines
the higher priority.
43
Figure 5.6
Examples of assigning
priorities to stereogenic centers
44
Label each compound as R or S.
a)
Cl
2
S
H
Br
H3C
b)
3
CH2Br
ClH2C
2
1
3
1
CH2Br
rotate
H3C
OH
H3C
HO
2
2
CH2Cl
1
3
1
3
R
45
Label each compound as R or S.