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 S N 1 S N 2

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 ElectrophilesNucleophiles “loves electrons” – attracted to negative charge “loves nuclei” – attracted to positive charge may be positively charged or have deficit or electrons because atom is attached to very electronegative atom often negatively charged or lone pairs high electronegativity carbon of carbonyl group acids alkenes hydroxide –OH chloride –Cl ammonia – NH 3 Organic chemistry has special names for positively and negatively charged Parts of a molecule

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 GroupAdditionEliminationSubstitution AlkaneHalogenation (haloalkanes) AlkeneHydrohalogenation (monohaloalkanes) Hydration (di- haloalkanes) Hydrogenation (alkanes) Oxidation (-OH, C=O, COOH) AlcoholCondensation w/ COOH (ester) w/ conc. Acid or catalist (alkene) Oxidation (aldehyde, ketone, COOH) Carboxylic AcidCondensation with – OH (ester) AmineCondensation w/ COOH (amide)

REACTIONS

Halogenation of an alkane (substitution) Alkane + halogen gas  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  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  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  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  1,2-dichloroethane (used as starting material for PVC) Uses: Br 2 dissolved in dichloromethane is used to distinguish between alkenes and alkanes. If reddish- brown color of Br 2 disappears when added to unknown, the unknown has alkenes in it.

Hydrogenation (addition) Alkene + hydrogen gas (with catalyst)  alkane Hydrogenation is saturating an unsaturated hydrocarbon Also called reduction Heterogeneous Catalyst: Pd or PtO 2 (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  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  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  alkene Reaction conditions: 170 ̊ and concentrated sulfuric acid or H 3 PO 4 and a catalyst or Al 2 O 3 and a catalyst Condensation reaction: produces water

Polymerization Polyethylene Reaction: n CH 2 =CH 2  (-CH 2 -CH 2 -) 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 GroupAdditionEliminationSubstitution AlkaneHalogenation (haloalkanes) AlkeneHydrohalogenation (monohaloalkanes) Hydration (di- haloalkanes) Hydrogenation (alkanes) Oxidation (-OH, C=O, COOH) AlcoholCondensation w/ COOH (ester) w/ conc. Acid or catalist (alkene) Oxidation (aldehyde, ketone, COOH) Carboxylic AcidCondensation with – OH (ester) AmineCondensation w/ COOH (amide)