REACTIONS OF ORGANIC COMPOUNDS

MAIN TYPES OF REACTIONS in Organic Chem 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

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 1,1,2,2-tetrabromopropane Asymmetrical

ADDITION REACTIONS: ALKYNES May occur as two addition reactions: + +

Addition Takes place with unsaturated compounds which are usually more reactive that saturated compounds Takes place with both Double and Triple bonds Two atoms are added across the electron rich bond What can be added? X2 H2 H2O HX

Addition Addition of halogen Normally occurs dissolved in a solvent such as CCl4 Alkenes form dihaloalkanes Alkynes produce dihaloalkenes or tetrahaloalkanes 1,2-dichloroethane

Addition Addition of Hydrogen Known as Hydrogenation Catalysts normally used such at Pt, Pd or Ni Known as Hydrogenation Alkene becomes an alkane Alkyne becomes and alkene or alkane H2C=CH2 + H2  Heat, catalyst H H H-C-C-H

Addition Addition of Hydrogen Halides (HX) HX = HCl, HBr, HI (Not HF) Alkene becomes an alkyl Halide Alkynes form Monohalo alkenes or dihaloalkanes with the halogens on the same carbon H2C=CH2 + HX  H H H-C-C-H H X HC=CH + HX  H-C-C-H H X + HX 

2) SUBSTITUTION REACTION A hydrogen atom or functional group is replaced by a different functional group To recognize: two compounds react to form two products. 2-bromobutane butan-2-amine

Substitution Reactions Any reaction in which one atom is replaced by another Used to place a halogen onto an alkane The products always are a halocarbon and the acid of the halogen (ex: hydrobromic acid) Needs ultraviolet light to initiate the reaction Provides the high energy needed to form the excited state

Substitution Rxns What is the products formed in the following rxn? CH3CH3 + Br2  sunlight CH3 CH2Br + HBr (Why sunlight?)

SUBSTITUTION REACTION Aromatics Aromatics can only undergo substitution reactions

3) ELIMINATION REACTION atoms are removed form a molecule to form double bonds. Reverse of addition To recognize: One reactant breaks into two products

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

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

Elimination Rxns Any reaction in which atoms are eliminated from another molecule This can be done by Elimination of H2 Elimination of HX Elimination of H20

Elimination Reactions Loss of H2 - This process is often referred to as Dehydrogenation H H H-C-C-H  H2C=CH2 + H2 Heat, catalyst This type of rxn takes place in industry in what is know as a catalytic cracking unit

Elimination Rxns Loss of HX Alkyl halides can also undergo elimination. This is as known as dehydrohalogenation H H H-C-C-H  H2C=CH2 + HX H X Base (ex KOH) The base extract a proton (H+) and X- leaves

Elimination Rxns Loss of H2O Alcohols can undergo elimination via the loss of water. This is known as dehydration H H H-C-C-H  H2C=CH2 + H2O H OH Acid, heat a) The acid protonates the –OH group, water leaves Positive carbon remains behind b) An adjacent proton (H+) leaves next leaving the electron pair to form the double bond

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

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:

IV- Oxidation/Reduction Oxidation: the loss of electrons alternatively, the loss of H, the gain of O, or both Reduction: the gain of electrons alternatively, the gain of H, the loss of O, or both

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 where Hydrogen [H] is added

5) REDUCTION: Alkene

5) REDUCTION: Aldehyde/Ketone

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

Esterification Alcohol + Organic Acid = Water + Ester Used to make perfumes, scents and flavors Combination reaction which involves dehydration. The alcohol becomes the alkyl group and the acid becomes -oate Methyl propanoate

Aspirin – Made by Esterification HO C=O OH + H-O-C-CH3 O  Acetic acid Salicylic Acid HO C=O O-C-CH3 O (An alcohol and acid) Acetyl Salicylic Acid (Common Name) “Aspirin”

LecturePLUS Timberlake Ethers Contain an -O- between two carbon groups Formed by a condensation reaction of 2 alcohols to remove a molecule of water Methanol reacts with methanol to form CH3-O-CH3 methoxy methane Methanol reacts with ethanol to form CH3-O-CH2CH3 methoxy ethane LecturePLUS Timberlake

Amides Formed by the condensation reaction of an acid and an amine

Naming Amides Alkanamide from acid name O  methanamide (IUPAC) HC–NH2  propanamide (IUPAC) CH3CH2C–NH2

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 1-propanol

using alkyl halides to make amines Ammonia and other amines are good nucleophiles

Substitution Reactions of Aromatic Compounds Due to stabilization, aromatic compounds do not undergo addition reactions; they undergo substitution. Hydrogen is replaced by substituent.

Substitution Reactions of Aromatic Compounds Halogenation Friedel-Crafts Reaction Reactions of aromatic compounds often require a catalyst.

Organic Synthesis Problem set Draw out the synthesis sequence for each molecule below using the smaller molecules listed. Show complete structures for each step. Name each intermediate and by-product. State the reaction type in each step: Ethyl butanoate from any alkene and any alcohol. 2. ethylbenzene, from benzene, Chlorine gas and an alkane