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Transcript
Organic Reactions 1 Point #1 3 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 2 B) Elimination Reactions (like synthesis reactions because they result in larger compounds) • Condensation – Esterification – Formation of alkene – Formation of amide (peptide bond) 3 C) Substitution Reactions (like single or double replacement reactions where one atom/ion/functional group is replaced by another) • S N1 • S N2 4 Point #2 Basic process of organic reactions is through attraction of positively (electrophile) and negatively (nucleophile) charged parts of molecules 5 Electrophiles “loves electrons” = attracted to negative charge maybe positively charged or have deficit of electrons b/c atom is attached to very electronegative atom Nucleophiles “loves nuclei” = attracted to positive charge carbon of carbonyl group acids often negatively charged or lone pairs high electronegativity alkenes Hydroxide –OH Chloride –Cl Ammonia – NH3 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 Functional Group Addition Elimination Alkane Alkene Halogenation (haloalkanes) Hydrohalogenation (mono-haloalkanes,) Hydration (alcohols) Halogenation (dihaloalkanes) Hydrogenation (alkanes) Oxidation (-OH, C=O, COOH) Alcohol Condensation w/ COOH to (ester) w/ conc. acid or catalyst (alkene) Carboxylic Acid Condensation with –OH (ester) Condensation w/ COOH (amide) Amine Substitution Oxidation (aldehyde, ketone, COOH) 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 H H H + Cl Cl H h Cl H H H methane chloromethane h H Cl Cl H h H dichloromethane Cl Cl h Cl Cl chloroform also: trichloromethane Cl Cl Cl tetrachloromethane also: carbontetrachloride 11 -Reaction occurs through homolytic fission to form a free radical • Free radical is a element or molecule with an unpaired electron • Homolytic fission vs Heterolytic fission: Formation of free radicals often results in chain reactions – reaction keeps occurring until all reactant is used up. See polymerization notes form mechanism. – 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 H H H H + H Cl H Cl H H H H Hydrohalogenation of 1-propene H H H CH3 + H Cl H Cl H H H CH3 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. H H CH 3 + H H H Cl H C H H CH 3 + + H Cl- CH 3 H H H Cl 14 Example #3-Hydration – 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 ethene H H H H H acid + H H O H H O H H H Hydration of 1-propene H H H CH3 acid + H O H H H H O H H CH3 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. H H H H + Cl Cl Cl Cl H H H H 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 H H H H PtO2/Pd + H H H H H H H H 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 O OH + O propionic acid OH O + O propan-1-ol acetic acid OH acid + OH H2O ethyl acetate acid O + H2O O propan-1-ol propyl propionate 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 O H3 C OH + acetic acid also: ethanoic acid O H2N CH3 methanamine H3 C NH CH3 N-methylacetamide O + OH butyric acid also: butanoic acid CH3 HN CH3 N-methylmethanamine O CH3 N CH3 N,N-dimethylbutanamide 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 OH propan-1-ol + K2Cr2O7 acid O OH propanoic acid 21 Oxidation of alcohol (continued) • Partial Oxidation: primary alcohol + oxidizing agent aldehyde OH propan-1-ol + K2Cr2O7 acid O H 1-propanal 22 Oxidation of alcohol (continued) • Secondary alcohol + oxidizing agent ketone OH butan-2-ol + acid K2Cr2O7 O butan-2-one 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 H H3C CH OH H3C H H H H H C C H3C O CH2 OH H 3C CH 24