ISOMERS

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

5. ISOMERS 3 Types 2 Types 2 Types

6. Isomerism 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) https://www.youtube.com/watch?v=NgzFok_BA_0 Very Long but detailed explanation https://www.youtube.com/watch?v=kgA4BhE8iiw

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 C4H10 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 2-METHYLPROPANE branched n-BUTANE straight chain

11. 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) 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. 3 rd Type FUNCTIONAL GROUP ISOMERS ALCOHOLS and ETHERS ClassificationALCOHOL (C2H5O) ETHER (C2H5O) Name ETHANOL METHOXYMETHANE Functional Group Symbol R-OHR-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 ALDEHYDEKETONE FunctionalGroupSymbol R-CHOR-CO-R Physicalproperties 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 ACIDESTER Functional Group Symbol R-COOHR-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. 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 similar chemical properties small difference physical properties FunctionalGroup 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 resonance 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. 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. ethyl methyl methyl determine name for side chains 1-hexene 1-hexene

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