CHAPTER 2: REACTIONS OF ORGANIC COMPOUNDS

MAIN TYPES OF REACTIONS in Organic Chem I wonder why she wrote it in Japanese Look! I think she’s using it to blow her nose Whew! That was easy!  She called it a Blood Bath! Addition Substitution Elimination Oxidation Reduction Condensation Hydrolysis Combustion Types of Substitution Reactions

1) ADDITION REACTION Atoms added to a double or triple bond Alkene or Alkyne undergoes addition reaction to break a double or triple bond Example: Reactant XY added to alkene makes alkane To recognize: Two reactants make 1 product LOOK FOR: check if C atoms in product(s) are bonded to more atoms than C atoms in reactant

1) ADDITION REACTIONS Common atoms that can be added to an alkene or alkyne H and OH (from H2O ) H and X (from H-X) where X= Cl , Br, or I X and X from (X2) where X= Cl , Br, or I H and H (from H2)

EXAMPLES: Addition Reactions 1) 2)

ADDITION REACTIONS: ALKENES Symmetrical molecule reacts with asymmetrical molecule to give one product. Symmetrical Asymmetrical

Which product is favoured ? RULES FOR ADDITION Two asymmetrical molecules react to give two products. Example: Which product is favoured ? + or Asymmetrical Asymmetrical

“MARKOVNIKOV’S” Rule "the rich get richer" The carbon atom with the largest number of carbon atoms gets the X (halogen) or OH bind to it Therefore 2- bromobutane is favoured 2-bromobutane Major product + Minor Product 1-bromobutane

ADDITION REACTIONS: ALKYNES Also follow Markovnikov’s rule when asymmetrical **if in excess 1,1,2,2-tetrabromopropane Asymmetrical

ADDITION REACTIONS: ALKYNES May occur as two addition reactions: + First product would be the only product if reacted with limited amount of bromine. +

2) SUBSTITUTION REACTION A hydrogen atom or functional group is replaced by a different atom or functional group To recognize: two compounds react to form two products. LOOK FOR: Two compounds react to form two different compounds Carbon atoms are bonded to the same number of atoms in product and reactant 2-bromobutane 2-butanamine

2) SUBSTITUTION REACTION 1) CH3CH2-OH + HI CH3CH2-I + H2O 2) 3) ethanol iodoethane Alcohols and haloalkanes undergo substitution reactions relatively easily 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 Alkanes also undergo substitution reactions Alkanes are relatively unreactive, thus a lot of energy is required (UV light) to catalyze rxn 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 REACTION Aromatics Aromatics can only undergo substitution reactions

SUBSTITUTION REACTION Alcohols Halogens in HCl, HBr or HI can substitute the OH group of alcohol or the reverse. For Ex: CH3-CH2-OH + HCl CH3-CH2Cl + H2O The reverse reaction: CH3-CH2Cl + OH- CH3-CH2-OH + Cl- (from water)

3) ELIMINATION REACTION atoms are removed form a molecule to form double bonds. Reverse of addition To recognize: One reactant breaks into two products LOOK FOR: check if C atoms in product(s) are bonded to less atoms than C atoms in reactant

ELIMINATION REACTION: Alcohol undergo elimination when heated in presence of strong acids, for example: H2SO4 Example:

ELIMINATION REACTION: Alkyl Halides Undergo elimination to produce alkenes Bromoethane ethene hydrobromic acid

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 (major product) (minor product)

4) OXIDATION & 5) REDUCTION REACTIONS Change in the number of H or O atoms bonded to C Always occur together One reactant is oxidized while the other is reduced For now, lets focus on reactant only…

4) OXIDATION Carbon atom forces more bonds to Oxygen or less to Hydrogen For example: formation of C=O bond Occurs in presence of oxidizing agents [O] such as KMnO4, K2Cr2O7, and O3 For now, focus on organic reactant only Some oxidation reactions can also be classified as elimination reactions

4) OXIDATION: Alcohol Alcohol oxidation can form an aldehyde or ketone Primary Alcohol Secondary Alcohol Tertiary Alcohols do not oxidize

4) OXIDATION: Aldehyde Aldehydes undergo oxidation to produce carboxylic acid Example:

5) REDUCTION REACTION Carbon atom forms fewer bonds to Oxygen or more bonds to Hydrogen Aldehydes, ketones and carboxyliic acids can be “reduced” to alcohols Alkenes and alkynes can be reduced to become alkanes Occurs in the presence of reducing agents such as LiAlH4, and H2/Pt where Hydrogen [H] is added Some reduction reactions can also be classified as addition reactions Lithium aluminium hydride (hydrogen over a platinum catalyst)

5) REDUCTION: Alkene

5) REDUCTION: Aldehyde/Ketone Aldehyde or ketone Reducing agent alcohol

6) CONDENSATION Water is usually produced in this reaction two molecules combine to form a single, bigger molecule. Water is usually produced in this reaction A carboxylic acid and alcohol can condense to form an ester called “ esterification” A carboxylic acid and amine can condense to form an amide LOOK FOR: Hydroxyl group from one molecule and a hydrogen atom from a second molecule being removed, and water being produced Flavours and smells of fruits and spices are due to ester compounds

Condensation carboxylic amine amide water acid

7) HYDROLYSIS water adds to a bond splitting it into two Reverse of a condensation reaction Water can add to an ester or amide bond Ester + water makes a carboxylic acid and alcohol Amide + water makes a carboxylic acid and amine LOOK FOR: a large molecule containing an ester or amide reacting with water to produce to smaller molecules  example #1 Both the condensation reaction and hydrolysis reaction are catalyzed by acid 1-propanol

8) 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 CxHy + O2(g)  CO2(g) + H2O(g) + energy HC + O2(g)  C(s) + CO(g) + CO2(g) + H2O(g) + energy

POLYMERS very long molecules made by linking small molecules called monomers Example: -PET(Polyethylene terephthalate ) polymers - Plastics are polymers that can be heated and moulded into specific shapes and forms -Polyethene is made from monomer of

POLYMERS can be synthetic or natural Synthetic polymers man made polymer like plastics and polyester Natural polymers found in nature like glucose and silk

ADDITION Polymerization Monomers added together through multiple addition reactions Examples: Examples Pg 83: Table 2.1

CONDENSATION Polymerization monomers are joined together by the formation of ester or amide bond Water created as a side product Example: Polyesters contain many ester bonds Nylon (polyamide) contains many amide bonds