Lecture and Chapter 17 Notes

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University of Toronto St. George
Thavarajah/ Woolley/ Nitz

CHM138H1 Jasmyn Lee Chapter 17: Alcohols and IR Spectroscopy 17.1 Naming Alcohols and Phenols Nomenclature 17.2 Properties of Alcohols and Phenols Structure Physical Properties  Interact by: 1) Dipole-Dipole Interactions 2) Hydrogen Bonding – allows for higher boiling point  Constitutional Isomers Acidity and Basicity of Alcohols  In strong acids, alcohols can act as bases: o Reversibly protonated by strong acids to yield oxonium ions, ROH2+  In dilute aqueous solution, alcohols are weakly acidic: o Dissociate slightly by donating H+ to 2 O, generating 3 O+ and an alkoxide ion, RO or a phenoxide ion, ArO - o K a [RO-][H 3+] / [ROH] pK a -logK a  An alcohol is more acidic if its o Conjugate base has resonance and is therefore stabilized o If it has EWG (inductive effects) to delocalize the negative charge on the conjugate base Phenol Acidity 1 CHM138H1 Jasmyn Lee 17.3 Preparations of Alcohols 1) (Indirect) Hydration of Alkenes a. Hydroboration – oxidation yields the product of syn, non-Markovnikov hydration b. Oxymercuration-demercuration – yields the product of Markovnikov hydration 2) Hydroxylation – OsO f4llowed by a reduction with NaHSO 3 17.4 Alcohols from Carbonyl Compounds: Reduction 3) Reduction of Carbonyl Functional Groups o NaBH –4mild reducing agent (reduces only aldehydes and ketones) o LiAlH4– stronger reducing agent – reduces all carbonyl compounds a. Aldehydes and Ketones: NaBH in4water or alcohols or LiAlH i4 ether  Aldehydes  1° alcohols  Ketones  2° alcohols 2 CHM138H1 Jasmyn Lee b. Esters and Carboxylic Acids: LiAlH in ether 4 17.5 Alcohols from Carbonyl Compounds: Grignard Reactions 4) Reactions of Carbonyls with Grignard Reagents  Recall: Grignard Reagents – prepared by reaction of organohalides with magnesium  Grignard reagents react with carbonyl compounds to yield alcohols o Formaldehyde  1° alcohol o Aldehydes  2° alcohol o Ketones  3° alcohol  Ester 3° alcohols in which two of the substituents bonded to the hydroxyl-bearing carbon have come from the Grignard reagent  Carboxylic Acids  hydrocarbon and the magnesium salt of the acid; does not yield an alcohol 17.6 Reactions of Alcohols 1) Deprotonation o Reaction with strong bases (pKa of conjugate acid > ~18) o Reaction with NaH (strong base) o Reaction with organolithium 3 CHM138H1 Jasmyn Lee 2) Conversion of “-OH” into Better Leaving Groups Conversion of Alcohols into Alkyl Halides  3° Alcohols o SN1 Reaction o Acid protonates the hydroxyl oxygen atom, water is expelled to generate a carbocation o Cation reacts with nucleophilic halide ion to give the alkyl halide product  1° and 2° alcohols o L=SOCl2or PBr 3 o Converts the –OH into a better leaving group o Inversion at the stereocenter Conversion of Alcohols into Tosylates  Alcohols react with p-toluenesulfunul chloride (tosyl chloride, p-TosCl) in pyridine solution to yield alkyl Tosylates, ROTos  Only the O-H bond of the alcohol is broken in this reaction o C-O bond remains intact o SN1 and SN2 reactions  Converts the –OH into a better leaving group  Retention at the stereocenter 4 CHM138H1 Jasmyn Lee 3) Dehydration to Yield Alkenes: 3° Alcohols  Acid catalyzed reaction of 3° Alcohols o Usually follow Zaitsev’s rule and yields the more stable alkene o E1 process o 3 step mechanism  Protonation of the alcohol oxygen  Unimolecular loss of water to generate a carbocation intermediate
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