1. Organic Reactions
SCH4U – Unit B

2. Types of organic reactions
Addition
Elimination
Substitution
Condensation (dehydration synthesis)
Esterfication
Hydrolysis
Oxidation
Reduction
Combustion
Complete
Incomplete

3. Addition
Reaction in which atoms are added to a carbon-carbon double or triple bond
LOOK FOR: check if C atoms in product(s) are bonded to more atoms than C atoms in reactant
Alkenes and alkynes generally react with one of four reactants:
H2, H-H  example #1
H2O, H-OH  example #2
Acid Halides, H-X (X = F, Cl, Br, I)  example #3
Diatomic Halogens, X-X  example #4

4. Addition
Example #1
2-butene
butane

5. Addition
Example #2
2-butanol
2-butene

6. Addition
Example #3
2-fluoro butane

7. Addition
Example #4
2,3-difluoro butane

8. Addition
When adding halogens to an alkyne, a total of four atoms can be added
The amounts of the halogen reactant must be considered:
Excess  example #5
Limited  example #6

9. Addition
Example #5
(excess halogen)
2,2,3,3-tetrafluoro butane

10. Addition
Example #6
(limited halogen)
2,3-difluoro 2-butene

11. Addition
If the alkene/alkyne contains many C atoms and is reacting with a small molecule, isomers may form  example #7
If the small molecule reacts with an asymmetrical alkene, can use Markinnikov’s rule to predict the more abundant isomer  example #8
Markovnikov’s rule: H atom of a small molecule will attach to C atom of double bond that is already bonded to the most H atoms

12. Addition
Example #7
50% 2-bromo pentane
50% 3-bromo pentane

13. Addition
Example #8
2-bromo pentane

14. Elimination
Reaction in which atoms are removed from an organic molecule to form a double bond
LOOK FOR: check if C atoms in product(s) are bonded to less atoms than C atoms in reactant
Basically, this is the reverse of an addition reaction
Methods of undergoing elimination reactions:
Heat and strong acid (catalyst)  used for alcohols  example #1
Heat and strong base (catalyst)  used for haloalkanes  example #2

15. Elimination
Example #1

16. Elimination
Example #2

17. opposite of Markovnikov’s Rule
Elimination
If an asymmetrical molecule undergoes an elimination reaction, constitutional isomers can form  example #3
General rule: H atom most likely to be removed from C atom with most C-C bonds
“The poor get poorer!”
opposite of Markovnikov’s Rule
Called Zaitsev’s rule

18. Elimination
Example #3
(major product)
(minor product)

19. Substitution
Reaction in which a hydrogen atom or functional group is replaced by a different atom or functional group
LOOK FOR:
Two compounds react to form two different compounds
Carbon atoms are bonded to the same number of atoms in product and reactant

20. Substitution
Alcohols and haloalkanes undergo substitution reactions relatively easily
Alcohol reacts with acids containing a halogen (HCl, HBr, etc.) to produce a haloalkane  example #1
Haloalkane reacts with hydroxide to produce an alcohol  example #2
Haloalkanes also react with bases to undergo elimination reactions
Thus, hard to control reactions of haloalkanes with bases
For the purposes of our course:
OH– = substitution reaction
NaOCH2CH3 = elimination reaction

21. Substitution
Example #1
ethanol chloroethane

22. Substitution
Example #2
chloroethane ethanol

23. Substitution Alkanes also undergo substitution reactions
Alkanes are relatively unreactive, thus a lot of energy is required (UV light) to catalyze rxn
Alkanes react with chlorine and bromine to form haloalkanes
If enough of the halogen is present, a mix of organic compounds forms  example #3
Ultimately, because of the mix of products, this process is not used to produce haloalkanes

24. Substitution
Example #3

25. Substitution
Aromatic hydrocarbons (benzene derivatives) are also stable
Require a catalyst to react with chlorine and bromine  example #4

26. Substitution
Example #4
benzene bromobenzene

27. Condensation
Reaction in which two molecules combine to form a larger molecule, producing a small, stable molecule, usually water, as a second product or functional group
LOOK FOR: Hydroxyl group from one molecule and a hydrogen atom from a second molecule being removed, and water being produced
EXTREMELY IMPORTANT IN BIOLOGY!
Generally forms an amide bond when it occurs between ~COOH and ~NH2

28. Condensation
Example #1
carboxylic amine amide water
acid

29. Condensation
Example #2

30. Esterification (condensation)
Reaction of a carboxylic acid with an alcohol to form an ester and water
Specific type of condensation reaction  example #3
Catalyzed by a strong acid  H2SO4
Flavours and smells of fruits and spices are due to ester compounds
Can be duplicated in a lab
Production of synthesized ester compounds used to flavour juices, candies, etc.  example #4 (cherry flavour)

31. Esterification (condensation)
Example #3
carboxylic alcohol ester water
acid

32. Esterification (condensation)
Example #4
benzoic ethanol ethyl water
acid benzoate

33. Hydrolysis
Reaction in which a molecule is broken apart by adding hydroxyl group from a water molecule to one side of a bond and hydrogen atom of same water molecule to other side of bond
Basically, this is the reverse of a condensation reaction
LOOK FOR: a large molecule containing an ester or amide reacting with water to produce to smaller molecules  example #1

34. Hydrolysis
Example #1
ester water carboxylic alcohol
acid

35. Hydrolysis
Both the condensation reaction and hydrolysis reaction are catalyzed by acid  example #2
The double arrow indicates the reaction is reversible
How can we control the direction of a reversible reaction to favour one side of the equation???
EQUILIBRIUM! (Unit #4)

36. Hydrolysis
Example #2
carboxylic alcohol ester water
acid

37. Oxidation
Reaction in which a carbon atom forms more bonds to oxygen atoms or fewer bonds to hydrogen atoms (orgo)
Always occurs along with a reduction reaction
For organic chemistry, focus only on the organic compound
Some oxidation reactions can also be classified as elimination reactions

38. Oxidation Occurs when organic compound reacts with an oxidizing agent
KMnO4 = potassium permanganate
K2Cr2O7 = acidified potassium dichromate
O3 = ozone
Redox reactions are often left unbalanced  examples #1-3

39. Oxidation
Example #1
C atom has lost H atoms

40. Oxidation
Example #2
C atom has gained an O atom

41. Oxidation
Example #3
ethanol ethanal

42. Reduction
Reaction in which a carbon atom forms fewer bonds to oxygen atoms or more bonds to hydrogen atoms (orgo)
Always occurs along with an oxidation reaction
For organic chemistry, focus only on the organic compound
Some reduction reactions can also be classified as addition reactions

43. Reduction Occurs when organic compound reacts with an reducing agent
LiAlH4 = lithium aluminum hydride
H2/Pt = hydrogen gas over a platinum catalyst
Redox reactions are often left unbalanced  examples #1-3
Redox reactions will be covered in greater depth during ELECTROCHEMISTRY (Unit #5)!

44. Reduction Example #1 aldehyde or ketone alcohol
C atom has less bonds to O atom

45. Reduction
Example #2
alkene alkane
C atoms have more bonds to H atoms

46. Reduction Example #3 propanone 2-propanol
C atom has less bonds to O atom

47. Combustion
Type of reaction in which a compound reacts with oxygen to produce the oxides of elements that make up the compound
2 types:
Complete combustion: an excess of oxygen reacts with a hydrocarbon and produces carbon dioxide and water vapour, and releases energy
Incomplete combustion: reaction that occurs when insufficient oxygen is present; all elements in the fuel will not combine with oxygen to the greatest extent possible

48. Combustion Example #1 HC + O2(g)  CO2(g) + H2O(g) + energy Example #2
HC + O2(g)  C(s) + CO(g) + CO2(g) + H2O(g) + energy