Organic Reactions

Mr. Montjoy, guest lecturer 3 Basic Kinds of Organic Reactions

Addition Reactions 1. Hydrogenation • Saturating an unsaturated carbon chain • Alkene/yne to alkane/ene 2. Hydration • Alkene to alcohol 3. Halogenation/Hydrohalogenation • Alkane to haloalkane • Alkene to haloalkane 3 Basic Kinds of Organic Reactions

Elimination Reactions Condensation • Esterification • Formation of alkene • Formation of amide (peptide bond)

Substitution Reactions (like single or double replacement reactions where one atom/ion/functional group is replaced by another

• SN1

• SN2 Electrophiles & Nucleophiles The basic process of organic reactions occurs through attraction of positively and negatively charged parts of molecules Positively and Negatively Charged Parts of Organic Molecules

Organic chemistry has special names for positively and negatively charged Parts of a molecule

Electrophiles Nucleophiles • “loves electrons” – attracted to • “loves nuclei” – attracted to positive negative charge charge • may be positively charged or have • often negatively charged or deficit or electrons because atom is • lone pairs attached to very electronegative • high electronegativity atom

• carbon of carbonyl group • alkenes • acids • hydroxide –OH • chloride –Cl • ammonia – NH3 Positively and Negatively Charged Parts of Organic Molecules

• many organic reactions happen through the attraction of electrophiles for nucleophiles • in reaction mechanisms, generally electrons from nucleophile move to electrophile Alkanes are relatively inert compared to other functional groups

• Alkenes have pi bonds in which electrons are easily accessible because they aren’t trapped between two nuclei as sigma bonding electrons are. • Other functional groups have highly electronegative atoms like O, N or halogens Characteristic reactions for several functional groups reactions to recognize in bold, products indicated in ()

Functional Group Addition Elimination Substitution

Alkane Halogenation (haloalkanes) Alkene • Hydrohalogenation (monohaloalkanes) • Hydration (di- haloalkanes) • Hydrogenation (alkanes) • Oxidation (-OH, C=O, COOH) Alcohol Condensation Oxidation (aldehyde, • w/ COOH (ester) ketone, COOH) • w/ conc. Acid or catalist (alkene) Carboxylic Acid Condensation with – OH (ester) Amine Condensation w/ COOH (amide) REACTIONS Halogenation of an alkane (substitution)

• Alkane + halogen gas à haloalkane • Need ultraviolet light for reaction to occur • Depending on time and amount of reactants, more than one halogen can be added to the alkane Hydrohalogenation (addition)

• Alkene + acid halide à monohaloalkane • Halide ion adds to larger side (more substituted side of alkene) • Hydrohalogenation of ethene

• Hydrohalogenation of propene: notice that the chlorine adds to the larger side of the alkene Hydration (addition)

• Alkene + water in acidic solution à alcohol • Acid acts as catalyst in reaction • -OH group adds to larger side (more substituted side) of alkene • Uses: hydration is used for commercial manufacture of ethanol • Hydration of ethene

• Hydration of propene Halogenation (addition)

• Alkene + halogen gas à n,n+1-dihaloalkane • Diatomic gas has two atoms – both add to opposite sides of the double bond (and opposite sides of the molecule) • Uses: Chlorine + ethene à 1,2-dichloroethane (used as starting material for PVC)

• Uses: Br2 dissolved in dichloromethane is used to distinguish between alkenes and alkanes. If reddish-

brown color of Br2 disappears when added to unknown, the unknown has alkenes in it. Hydrogenation (addition)

• Alkene + hydrogen gas (with catalyst) à alkane • Hydrogenation is saturating an unsaturated hydrocarbon • Also called reduction

• Heterogeneous Catalyst: Pd or PtO2 (rxn occurs on a metal surface) • Uses: unsaturated vegetable oils are saturated to produce saturated fats (more solid at room temp than unsaturated) for margarines Esterification (elimination)

• Carboxylic acid + alcohol à ester + water • Reaction conditions: acidic solution • The OH group on the alcohol is replaced by the OOC-R group of the carboxylic acid • Condensation reaction: produces water • Uses: flavoring agents, plasticizers, as solvents in perfume, polyesters Amide formation (elimination)

• Carboxylic acid + amine à amide + water • Reaction condition: difficult to conduct in simple steps since amine (a base) and acid basically neutralize each other. To form amide, other reactions that “protect” important function groups are required • The OH group on the carboxylic acid is replaced by the amine (NH—R) • Condensation reaction: produces water • Uses: peptide bond formation, polymerization reactions to make nylons

video Condensation of alcohol (elimination)

• Condensation of alcohol à alkene • Reaction conditions: • 170̊ and concentrated sulfuric acid or

• H3PO4 and a catalyst or

• Al2O3 and a catalyst • Condensation reaction: produces water Polymerization

• Polyethylene

• Reaction: n CH2=CH2 à (-CH2-CH2-)n • Three kinds of polyethylene • HDPE = gallon milk cartons (more rigid) • LDPE = plastic bags, squeeze bottles (more flexible) • cPE = milk crates (very strong and rigid) Polymerization occurs when a molecule has two functional groups

• Polymers formed are copolymers because they are made of two different monomers • Polymers are formed in a step-growth method rather than a chain-growth method • In other words, molecules with 2 functional groups can grow from both ends instead of just one end as in polyethylene • Formation of a nylon (a poly- amide) Formation of a polypeptide

• Polypeptide is a chain of amino acids, each amino acid has one carboxylic acid and one amine group • Note that the polymerization here occurs because there are two different groups on the same molecule • Polypeptides are not, technically, polymers since they don’t have repeating units (R group is different) • Peptide bond between alanine and cysteine: Summary

Functional Group Addition Elimination Substitution