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Organic Reactions. SCH4U – Unit B. Types of organic reactions. Addition Elimination Substitution Condensation (dehydration synthesis) Esterfication Hydrolysis Oxidation Reduction Combustion Complete Incomplete. Addition.

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Organic Reactions


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    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’srule to predict the more abundant isomer  example #8 • Markovnikov’srule: 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. 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 ethanolchloroethane

    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 alkenealkane • 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