1. ISOMERS

2. Learning Objectives (LO)
- be able to write structural formulae from names and to name compounds from given structural formulae.
Examples should be drawn from alkanes, alkenes, alcohols and haloalkanes.
Know the many kinds of isomers, chain positional and functional group.
Know the difference between stereoisomers and structural isomers

3. Terminology
As this is mostly a review, most of these terms are already known.
Cyclic hydrocarbons
Benzene
Stereoisomers
Ethers, esters, carboxylic acids

4. halogen on carbon 1 (C4H10Cl) halogen on carbon 2 (C4H10 Cl)
What is an isomer?
It has the same molecular formula but a different structure
n-BUTANE
straight chain C4H10
2-METHYLPROPANE
Branched C4H10
1-CHLOROBUTANE
halogen on carbon (C4H10Cl)
2-CHLOROBUTANE
halogen on carbon (C4H10 Cl)
Methoxymetane or dimethyether
C2H6O
Ethanol C2H6O

5. ISOMERS
3 Types
2 Types
2 Types 5

6. Isomerism
Structural: same molecular formula but different structure
Stero: same structural formula, but different spatial arrangement
What is the difference between a structural isomer and a stereoisomer?
What is the difference between the 3
Structural Isomers?

7. TYPES OF ISOMERISM
CHAIN ISOMERISM
STRUCTURAL ISOMERISM
POSITION ISOMERISM
Same molecular formula but different structural formulae
FUNCTIONAL GROUP ISOMERISM
GEOMETRIC
ISOMERISM
Occurs due to the restricted rotation of C=C double bonds... two forms… E and Z (CIS and TRANS)
STEROISOMERISM
Same molecular formula but atoms occupy different positions in space.
OPTICAL
ISOMERISM
Occurs when molecules have a chiral centre. Get two non- superimposable mirror images.

8. Fuse School Isomers and Pb (5min)
Very Long but detailed explanation

9. 1st STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA
BUT DIFFERENT STRUCTURAL FORMULA
Chain different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
CHAIN ISOMERISM

10. CHAIN - STRUCTURAL ISOMER
Carbon chain different arrangements
Slightly different chemical properties
Slightly different physical properties (branching = lower boiling point)
Branching of the chain makes the molecule compact decreasing the surface area. Thus, intermolecular attractive forces, which depend upon the surface area, become small
Straight chain Branched molecule
- 0.5°C
straight chain
- 11.7°C
branched
Straight chains = larger surface =
more e- interactions = higher boiling point
n-BUTANE
straight chain
2-METHYLPROPANE
branched

11. POSITION OF A HALOGEN IN A HALOALKANE
2 nd Structural Isomer
POSITIONAL
molecule has the same carbon skeleton
molecule has the same same functional group... BUT
the functional group is in a different position
have similar chemical properties / different physical properties
Example
POSITION OF A HALOGEN IN A HALOALKANE
BUT
Name this 1 2 2
1-CHLOROBUTANE
halogen on carbon 1
2-CHLOROBUTANE
halogen on carbon 2
is NOT
3-CHLOROBUTANE
Moving the chlorine along the chain makes new isomers; the position is measured from the end nearest the functional group... the third example is 2- NOT 3-chlorobutane.
There are 2 more structural isomers of C4H9Cl but they have a longest chain of 3

12. STRUCTURAL ISOMERISM – POSITIONAL (2nd Example)
RELATIVE POSITIONS ON A BENZENE RING
1,2-DICHLOROBENZENE
ortho dichlorobenzene
1,3-DICHLOROBENZENE
meta dichlorobenzene
1,4-DICHLOROBENZENE
para dichlorobenzene

13. 3 rd STRUCTURAL ISOMERISM
FUNCTIONAL GROUP
molecules have same molecular formula molecules have different functional groups
molecules have different chemical properties
molecules have different physical properties
ALCOHOLS and ETHERS
Ex C2H5O
ALDEHYDES and KETONES
Ex C3H6O
ACIDS and ESTERS
Ex C3H6O2
MORE DETAILS FOLLOW

14. FUNCTIONAL GROUP ISOMERS
3 rd Type
FUNCTIONAL GROUP ISOMERS
ALCOHOLS and ETHERS
Classification ALCOHOL (C2H5O) ETHER (C2H5O)
Name
ETHANOL METHOXYMETHANE
Functional Group Symbol
R-OH R-O-R
Physical properties
Hydrogen Bonding No hydrogen bonding
High boiling point low boiling point
solubility in water insoluble in water
Chemical properties
Wide range of reactions Combusts but otherwise INERT

15. FUNCTIONAL GROUP ALDEHYDES and KETONES
Name
PROPANAL (C3H6O) PROPANONE (C3H6O)
Functional Group Type
ALDEHYDE KETONE
Functional Group Symbol
R-CHO R-CO-R
Physical properties
polar C=O bond gives polar C=O bond gives dipole-dipole interaction dipole-dipole interaction
Chemical properties
easily oxidised to acids oxidized
reduced to 1° alcohols reduced to 2° alcohols

16. STRUCTURAL ISOMERISM – FUNCTIONAL GROUP CARBOXYLIC ACIDS and ESTERS
Name
PROPANOIC ACID (C3H6O2) METHYL ETHANOATE (C3H6O2)
Classification
CARBOXYLIC ACID ESTER
Functional Group Symbol
R-COOH R-COOR
Physical properties
Hydrogen Bonding No hydrogen bonding
get higher boiling point and solubility in water
insoluble in water
Chemical properties
acidic fairly unreactive
react with alcohols hydrolysed to acids

17. FUNCTIONAL GROUP ISOMERISM
REVIEW ALL 3 TYPES
STRUCTURAL ISOMERS
Chain different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
Positional same carbon skeleton, same functional group
functional group is in a different position
small difference physical properties
Functional Group different functional group, different chemical properties
different physical properties…TOTALLY DIFFERENT
CHAIN ISOMERISM
POSITION ISOMERISM
FUNCTIONAL GROUP ISOMERISM

18. Nomenclature of Cycloalkanes
Cycloalkanes generally are shown as skeletal structures

19. Nomenclature of Cycloalkanes
Ring is the parent hydrocarbon unless the alkyl substituent has more carbons; in that case the substituent becomes the parent hydrocarbon
If only one substituent, no need to give it a number

20. Nomenclature of Cycloalkanes
If the ring has 2 substituents, list in alphabetical order and give number 1 to first named group

21. Aromaticity: Benzene - C6H6
Kekulé and the Structure of Benzene
Kekule benzene: two forms are in rapid equilibrium
• All bonds are 140 pm (intermediate between C-C and C=C)
• C–C–C bond angles are 120°
• Structure is planar, hexagonal

22. A Resonance Picture of Bonding in Benzene
hybrid
6 -electron delocalized
over 6 carbon atoms

23. Benzenes with two or more substituents:
• Choose numbers to get lowest possible values
• List substituents alphabetically with hyphenated numbers
• Non-systematic names, such as “toluene” can serve as parent

24. Disubstituted benzene: relative position of the substitutents
1,2-disubstituted: ortho (o-)
1,3-disubstituted: meta (m-)
1,4-disubstituted: para (p-)
Note: ortho, meta, and para are not used in systematic nomenclature 24

25. When the benzene ring is a substituent of a parent chain, it is
referred to as a phenyl group. The benzene ring is regarded
as a substituent when the parent chain has greater than six
carbons. The benzene ring is the parent when the longest
alkyl chain substituent is six carbons or less
A phenyl substituent (C6H5-) is often abbreviates as Ph- 25

26. choose the correct ending
Naming Practice!!!
choose the correct ending
ene

27. determine the longest carbon chain with the double bond
ene

28. assign numbers to each carbon
ene

29. assign numbers to each carbon
ene

30. attach prefix (according to # of carbons)
ene
1-hexene

31. determine name for side chains
ethyl
methyl
methyl
determine name for side chains
1-hexene
1-hexene

32. attach name of branches alphabetically
ethyl
methyl
methyl
attach name of branches alphabetically
2-ethyl-4-methyl-4-methyl-1-hexene