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Organic Chemistry Chapter 10
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Functional Groups
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The Key To Substitution Reactions The Leaving Group Goes
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Substitution Rx of R-OH Alcohols have polar groups which make substitution probable Alcohols have a strongly basic leaving group (OH - ) which make it not probable Protonation converts an alcohol to a good leaving group
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Mechanisms Wow… we get to draw one…….. From yahoo images
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Substitution Rx of R-OH HBr and HI work well for S N 2 reactions. HCl does not work well because Cl is a poorer nucleophile. Rate can be increased using ZnCl 2 –Zn 2+ is a Lewis Acid –Complexes with the O: (this weakens the C-O bond)
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Lucas Test.
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Rearramgement OH ya, don’t forget -
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“Grain” and “Wood Alcohol”.
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Conversion of Alcohols Use phosphorous trihalides or thionyl chloride –Better yields and no rearrangements –PCl 3, PBr 3, PI 3, or SOCl 2 Do the Mechanism…………………….. From yahoo images
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Conversion of Alcohols Pyridine is used as the solvent because it prevents formation of HCl or HBr and is a poor nucleophile.
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Conversion of Alcohols Commonly Used Methods for Converting Alcohols into Alkyl Halides –ROH + HBrRBr –ROH + HIRI –ROH + HClRCl –ROH + PBr 3 RBr –ROH + PCl 3 RCl –ROH + SOCl 2 RCl pyridine
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Sulfonate esters leaving groups Conversion of alcohols to sulfonyl chlorides –p-toluenesulfonyl chloride (tosyl chloride, TsCl) –methylsulfonyl chloride (mesyl chloride, MsCl) –trifluoromethanesulfonyl chloride (trif) They are up to 100 x better than Cl - as leaving groups
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Sulfonic acid has a pKa of – 6.5 wow!! That ought to be on stable base now don’t ya think?
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Reaction steps
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Dehydration of Alcohols Zaitsev’s Rule – more substituted formed
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Dehydration of Alcohols Dehydration is the reverse of Hydration –vary conditions to control equilibrium –Remove the alkene by distillation
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Dehydration of Alcohols Reaction may involve rearrangement
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Dehydration of Alcohols rearrangements with ring opening
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Dehydration of Alcohols E and Z produced, major product will have most bulky groups on opposite sides
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Dehydration with POCl 3 Uses a better leaving group Conditions are not as extreme Phosphorous oxychloride and pyridine No rearrangements Mildly basic conditions favor E2
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Oxidation of Alcohols From yahoo images Look at reaction and conditions For Primary and Secondary Alcohols
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Substitution Rx of Ethers Ethers can be activated by acid High concentration of HI, HBr will form the alkyl halide
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Ethers are relatively unreactive so they are frequently used as solvents –diethyl ether (ether) –tetrahydrofuran (THF) –1,4-dioxane –1,2-dimethoxyethane (DME) –methyl t-butyl ether (MTBE) Ethers as Solvents
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Addition of Peroxyacids Alkenes can be oxidized to an epoxide by a peroxyacid.
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Reactions of Epoxides Because of 3 membered ring, epoxides are much more reactive than normal ethers Undergo ring opening reactions at room temp
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Reactions of Epoxides (oxiranes) Formation of glycols (addition of H 2 O)
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Reactions of Epoxides (oxiranes)) Unsymmetrical additions yield the product resulting from Nu: attack on the more substituted carbon
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Reactions of Epoxides (oxiranes) Under basic conditions, Nu: attack is at the less hindered C The epoxide is reactive enough that you don’t need to protinate to get the reaction to go
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Crown Ethers
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Cyclic compounds with ether linkages Bind cations as “host” and “guest”
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Crown Ethers Naming – [x]-crown-Y X = total number of atoms in the ring Y = total number of oxygens
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Thiols and Sulfides
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Thiols are sulfur analogs of alcohols Also called mercaptans (mercury capturing)
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Thiols and Sulfides Thiols are named by adding suffix “thiol” Remember to keep the e Common names are alkyl mercaptans
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Physical Properties-Thiols The difference in electronegativity between S (2.5) and H (2.1) is 0.4. This creates a bond with low polarity show little association by hydrogen bonding have lower boiling points and are less soluble in water than alcohols of comparable MW
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Thiols act as Nucleophiles Thiolate anions are weak bases (weaker than alkoxides) and in protic solvents are better nucleophiles (better than alkoxides since they don’t H bond)
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Sulfides or thioethers Sulfur analogs are called sulfides or thioethers Most sulfides react readily to form sulfonium salts
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Sulfides or thioethers The sulfonium salt easily reacts in a substitution reaction:
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Organometallic Compounds So far, we have seen reaction in which carbon is bonded to a more electronegative atom. What happens when it is connected to a less electronegative atom?
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Organometallic Compounds A compound that contains a carbon-metal bond Organolithium Organomagnesium (Grignard Reagent)
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Organometallic Compounds
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Organometalics act as nucleophiles Reactions must be carried out in very dry solvents and nothing acidic Can be in the reaction mixture
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Organometallic Compounds The greater the polarity difference, the greater the reactivity of an organometalic reagent
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Coupling Reactions Gilman Reaction Heck Reaction Stille Reaction Suzuki Reaction
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Gilman Reagents Prepared from an organolithium reagent and copper(I) iodide Henry Gilman 1893-1986
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Gilman Reagents Gilman reagents can be used to form new carbon-carbon bonds by cross-coupling with alkyl or aryl or vinylic halides Henry Gilman 1893-1986 (Note: cannot use S N 2 with aryl or vinylic halides)
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The Heck Reaction
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The Stille Reaction
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The Suzuki Coupling
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