Chapter 17: Alcohols and Phenols

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Chapter 17 Alcohols and Phenols

• Based on McMurrys Organic Chemistry, 6th edition

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17.1 Naming Alcohols

• General classifications of alcohols based on
  substitution on C to which OH is attached
• Methyl (C has 3 Hs), Primary (1) (C has two
  Hs, one R), secondary (2) (C has one H, two
  Rs), tertiary (3) (C has no H, 3 Rs),

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IUPAC Rules for Naming Alcohols

• Select the longest carbon chain containing the
  hydroxyl group, and derive the parent name by
  replacing 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

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Many Alcohols Have Common Names

• These are accepted by IUPAC

• Systematic naming

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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

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17.2 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

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Alcohols Form Hydrogen Bonds

• A positively polarized ?OH hydrogen 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 point of the solution

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17.3 Properties of Alcohols and Phenols Acidity
and Basicity

• Weakly basic and weakly acidic
• Alcohols are weak Brønsted bases
• Protonated by strong acids to yield oxonium ions,
  ROH2

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Alcohols and Phenols are Weak Brønsted Acids

• Can transfer a proton to water to a very small
  extent
• Produces H3O and an alkoxide ion, RO?, or a
  phenoxide ion, ArO?

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Generating Alkoxides from Alcohols

• Alcohols are weak acids requires a strong base
  to form an alkoxide such as NaH, sodium amide
  NaNH2, and Grignard reagents (RMgX)
• Alkoxides are bases used as reagents in organic
  chemistry

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pKa Values for Typical OH Compounds
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Nitro-Phenols

• Phenols 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

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17.4 Preparation of Alcohols an Overview

• Alcohols are derived from many types of compounds
• The alcohol hydroxyl can be converted to many
  other functional groups
• This makes alcohols useful in synthesis

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Review Preparation of Alcohols by Regiospecific
Hydration of Alkenes

• Hydroboration/oxidation syn, non-Markovnikov
  hydration
• Oxymercuration/reduction Markovnikov hydration

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Preparation of 1,2-Diols

• Review Cis 1,2-diols from hydroxylation of an
  alkene with OsO4 followed by reduction with
  NaHSO3
• In Chapter 18 Trans-1,2-diols from
  acid-catalyzed hydrolysis of epoxides

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Reduction of Aldehydes and Ketones with Hydride
Donors

• Aldehydes gives primary alcohols
• Ketones gives secondary alcohols

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Reduction of Carboxylic Acids and Esters

• Carboxylic acids and esters are reduced to give
  primary alcohols
• LiAlH4 is used because NaBH4 is not effective

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17.6 Alcohols from Reaction of Carbonyl Compounds
with Grignard Reagents

• Alkyl, aryl, and vinylic halides react with
  magnesium in ether or tetrahydrofuran to generate
  Grignard reagents, RMgX
• Grignard reagents react with carbonyl compounds
  to yield alcohols

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Examples of Reactions of Grignard Reagents with
Carbonyl Compounds
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Reactions of Esters and Grignard Reagents

• Yields tertiary alcohols in which two of the
  substituents carbon come from the Grignard
  reagent
• Grignard reagents do not add to carboxylic acids
  they undergo an acid-base reaction, generating
  the hydrocarbon of the Grignard reagent

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Grignard Reagents and Other Functional Groups in
the Same Molecule

• Can't be prepared if there are reactive
  functional groups in the same molecule, including
  proton donors

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17.7 Some Reactions of Alcohols

• Two general classes of reaction
• At the carbon of the CO bond
• At the proton of the OH bond

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Dehydration of Alcohols to Yield Alkenes

• The general reaction forming an alkene from an
  alcohol through loss of O-H and H (hence
  dehydration) of the neighboring CH to give ?
  bond
• Specific reagents are needed

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Substitutions
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Protecting Groups
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Synthesis of Phenols
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Reactions of Phenols
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