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Basic Organic Reactions: Addition, Elimination, and Substitution

Explore the fundamental kinds of organic reactions, including addition, elimination, and substitution, along with reaction mechanisms and characteristic reactions of functional groups.

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Basic Organic Reactions: Addition, Elimination, and Substitution

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  1. Organic Reactions

  2. Point #13 basic kinds of reactions A) Addition Reactions (like synthesis reactions) • Hydrogenation • saturating an unsaturated carbon chain • alkene/yne to alkane • Hydration • alkene to alcohol • Halogenation/Hydrohalogenation • alkane to haloalkane • alkene to haloalkane

  3. B) Elimination Reactions (like synthesis reactions because they result in larger compounds) • Condensation • Esterification • Formation of alkene • Formation of amide (peptide bond)

  4. C) Substitution Reactions (like single or double replacement reactions where one atom/ion/functional group is replaced by another) • SN1 • SN2

  5. Point #2 Basic process of organic reactions is through attraction of positively (electrophile) and negatively (nucleophile) charged parts of molecules

  6. many organic reactions happen through the attraction of electrophiles for nucleophiles • in reaction mechanisms, curly arrows show how electrons move – generally electrons from nucleophile move to electrophile

  7. Point #3 Alkanes/Alkenes are relatively inert compared to other functional groups A) Alkenes have pi bonds in which electrons are easily accessible b/c they aren’t trapped between two nuclei as sigma bonding electrons are.

  8. B) Other functional groups have highly electronegative atoms like O, N or halogens

  9. The table below gives the characteristic reactions for several functional groups

  10. Reactions Example #1-Halogenation of alkane • Alkane + halogen gas  haloalkane • Need ultraviolet light for rxn to occur • Depending on time and amount of reactants, more than one halogen can added to the alkane

  11. -Reaction occurs through homolytic fission to form a free radical Formation of free radicals often results in chain reactions – reaction keeps occurring until all reactant is used up. See polymerization notes form mechanism. • Free radical is a element or molecule with an unpaired electron • Homolytic fission vs Heterolytic fission: • Fission means splitting apart • Heterolytic means that one atom takes both electrons in the bond and two ions are formed. • Homolytic means the bond is split in half – each side takes 1 electron and 2 free radicals are formed

  12. Example #2-Hydrohalogenation Hydrohalogenation of ethene • Alkene + acid halide  monohaloalkane • Halide ion adds to larger side (more substituted side of alkene) if there is one Hydrohalogenation of 1-propene

  13. Reaction occurs through heterolytic fission to form an ion • The first step is the attraction of the electrophile (Hydrogen ion) to the electrons in the pi bond. This forms a carbocation. • The carbocation that is more substituted (has more carbons attached to it) is the most stable. • The negatively charged halogen (nucleophile) adds to the carbocation to form the halogenated alkene.

  14. Example #3-Hydration Hydration of ethene • Alkene + water in acidic solution  alcohol • Acid acts as catalyst in rxn • –OH group adds to larger side (more substituted side) of alkene • Uses: hydration is used for commercial manufacture of ethanol Hydration of 1-propene

  15. Example #4 -Halogenation • Alkene + halogen gas  1,2-dihaloalkane • Diatomic gas has two atoms – both add to opposite sides of the double bond (and opposite sides of the molecule) • Uses: Chlorine + ethane  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.

  16. Example #5 Hydrogenation • Alkene + Hydrogen gas (with catalyst) alkane • Hydrogenation is saturating an unsaturated hydrocarbon • Addition Reaction • 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

  17. Example #6 Esterification • Carboxylic acid + alcohol  ester + water • Reaction conditions: acidic solution • The OH group on the carboxylic acid is replaced by the alcohols O-R group • Condensation reaction: produces water • Uses: flavouring agents, plasticizers, as solvents in perfume, polyesters

  18. Examples #7 Amide formation • Carboxylic acid + amine  amide + water • Reaction condition: difficult to conduct in simple steps • The OH group on the carboxylic acid is replaced by the amine (NH-R) • Condensation rxn: produces water • Uses: peptide bond formation, polymerization reactions to make nylons

  19. Example #8 Oxidation of alcohol • Alcohol + oxidizing agent  COOH (1, complete) /Aldehyde (1, partial)/Ketone (2) • Obviously an Oxidation reaction • Reaction condition: aqueous, acidic solution. The carboxylic acid and the aldehyde can be obtained through different experimental set-ups • Distill to get aldehyde • Heat under reflux to get COOH

  20. Oxidation of alcohol (continued) • Complete Oxidation: primary alcohol + oxidizing agent  carboxylic acid

  21. Oxidation of alcohol (continued) • Partial Oxidation: primary alcohol + oxidizing agent  aldehyde

  22. Oxidation of alcohol (continued) • Secondary alcohol + oxidizing agent  ketone

  23. Example #9 Condensation of alcohol • Condensation of alcohol alkene • Reaction conditions: • 170 and concentrated sulfuric acid or • H3PO4 and a catalyst or Al2O3 and a catalyst

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