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1、CH 17: Alcohols and Phenols,Renee Y. Becker CHM 2211 Valencia Community College,1,Alcohols and Phenols,Alcohols contain an OH group connected to a saturated C (sp3) They are important solvents and synthesis intermediates Enols also contain an OH group connected to an unsaturated C (sp2) Phenols cont
2、ain an OH group connected to a carbon in a benzene ring,2,Alcohols and Phenols,Methanol, CH3OH, called methyl alcohol, is a common solvent, a fuel additive, produced in large quantities Ethanol, CH3CH2OH, called ethyl alcohol, is a solvent, fuel, beverage Phenol, C6H5OH (“phenyl alcohol”) has divers
3、e uses - it gives its name to the general class of compounds,3,Naming Alcohols,General classifications of alcohols based on substitution on C to which OH is attached,4,IUPAC Rules for Naming Alcohols,Select the longest carbon chain containing the hydroxyl group, and derive the parent name by replaci
4、ng the -e ending of the corresponding alkane with -ol Number the chain from the end nearer the hydroxyl group Number substituents according to position on chain, listing the substituents in alphabetical order,5,6,Many Alcohols Have Common Names,These are accepted by IUPAC,7,Example 1: Give the IUPAC
5、 names for these compounds,2,1,3,4,8,Example 2: Draw the following structures,2-Ethyl-2-buten-1-ol 3-Cyclohexen-1-ol 1,4-Pentanediol,9,Naming Phenols,Use “phene” (the French name for benzene) as the parent hydrocarbon name, not benzene Name substituents on aromatic ring by their position from OH,10,
6、Properties of Alcohols and Phenols: Hydrogen Bonding,The structure around O of the alcohol or phenol is similar to that in water, sp3 hybridized Alcohols and phenols have much higher boiling points than similar alkanes and alkyl halides,11,Alcohols Form Hydrogen Bonds,A positively polarized OH hydro
7、gen atom from one molecule is attracted to a lone pair of electrons on a negatively polarized oxygen atom of another molecule This produces a force that holds the two molecules together These intermolecular attractions are present in solution but not in the gas phase, thus elevating the boiling poin
8、t of the solution,12,Properties of Alcohols and Phenols: Acidity and Basicity,Weakly basic and weakly acidic Alcohols are weak Brnsted bases Protonated by strong acids to yield oxonium ions, ROH2+,13,Alchols and Phenols are Weak Brnsted Acids,Can transfer a proton to water to a very small extent Pro
9、duces H3O+ and an alkoxide ion, RO, or a phenoxide ion, ArO,14,15,Relative Acidities of Alcohols,Simple alcohols are about as acidic as water Alkyl groups make an alcohol a weaker acid The more easily the alkoxide ion is solvated by water the more its formation is energetically favored Steric effect
10、s are important,16,Stronger acid,17,Inductive Effects,Electron-withdrawing groups make an alcohol a stronger acid by stabilizing the conjugate base (alkoxide),Stronger acid,18,Generating Alkoxides from Alcohols,Alcohols are weak acids requires a strong base to form an alkoxide such as NaH, sodium am
11、ide NaNH2, and Grignard reagents (RMgX) Alkoxides are bases used as reagents in organic chemistry,19,Example 3:,20,Phenol Acidity,Phenols (pKa 10) are much more acidic than alcohols (pKa 16) due to resonance stabilization of the phenoxide ion Phenols react with NaOH solutions (but alcohols do not),
12、forming soluble salts that are soluble in dilute aqueous A phenolic component can be separated from an organic solution by extraction into basic aqueous solution and is isolated after acid is added to the solution,21,Substituted Phenols,Can be more or less acidic than phenol itself An electron-withd
13、rawing substituent makes a phenol more acidic by delocalizing the negative charge Phenols with an electron-donating substituent are less acidic because these substituents concentrate the charge,22,Example 4:,p-Nitrobenzyl alcohol is more acidic than benzyl alcohol. Explain.,23,Nitro-Phenols,Phenols
14、with nitro groups at the ortho and para positions are much stronger acids The pKa of 2,4,6-trinitrophenol is 0.6, a very strong acid,24,Preparation of Alchols: an Overview,Alcohols are derived from many types of compounds The alcohol hydroxyl can be converted to many other functional groups This mak
15、es alcohols useful in synthesis,25,Review: Preparation of Alcohols by Regiospecific Hydration of Alkenes,Hydroboration/oxidation: syn, non-Markovnikov hydration Oxymercuration/reduction: Markovnikov hydration,26,Preparation of 1,2-Diols,Review: Cis 1,2-diols from hydroxylation of an alkene with OsO4
16、 followed by reduction with NaHSO3 In Chapter 18: Trans-1,2-diols from acid-catalyzed hydrolysis of epoxides,27,Alcohols from Reduction of Carbonyl Compounds,Reduction of a carbonyl compound in general gives an alcohol Note that organic reduction reactions add the equivalent of H2 to a molecule,28,Reduction of Aldehydes and Ketones,Aldehydes gives primary alcohols Ketones gives secondary alcohols,29,Catalytic Hydrogenation:,30,Reduction Reagent: Sodium Borohydride,NaBH4 is not
