Organic Reactions SCH4U – Unit B

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

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

Addition Example #1 2-butene butane

Addition Example #2 2-butanol 2-butene

Addition Example #3 2-fluoro butane

Addition Example #4 2,3-difluoro butane

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

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

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

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

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

Addition Example #8 2-bromo pentane

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

Elimination Example #1

Elimination Example #2

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

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

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

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

Substitution Example #1 ethanol chloroethane

Substitution Example #2 chloroethane ethanol

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

Substitution Example #3

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

Substitution Example #4 benzene bromobenzene

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

Condensation Example #1 carboxylic amine amide water acid

Condensation Example #2

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)

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

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

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

Hydrolysis Example #1 ester water carboxylic alcohol acid

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)

Hydrolysis Example #2 carboxylic alcohol ester water acid

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

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

Oxidation Example #1 C atom has lost H atoms

Oxidation Example #2 C atom has gained an O atom

Oxidation Example #3 ethanol ethanal

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

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)!

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

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

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

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

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