Chem 150 Unit 8 - Organic Molecules III Alcohols, Thiols, Ethers, Aldehydes and Ketones

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Chem 150Unit 8 - Organic Molecules IIIAlcohols,
Thiols, Ethers, Aldehydes and Ketones

• In this unit we continue surveying some of the
  families of organic molecules that play important
  roles in biochemistry looking both at their
  physical and chemical properties. The Group VIA
  elements, oxygen and sulfur, typically form two
  covalent bonds to attain a filled valence shell.
  The families that include oxygen and sulfur with
  two single bonds include alcohols C-O-H, ethers
  C-O-C, thiols C-S-H, sulfides C-S-C and
  disulfides C-S-S-C. We will also look at two more
  important carbonyl containing functional groups,
  aldehydes and ketones.

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Introduction

• The organic groups covered in this Unit all have
  important biological roles
• Alcohols
• Triglycerides
• Amino acids and proteins
• Ethers
• Biologically active molecules
• Thiols
• Amino acids and proteins
• Odorants
• Sulfides
• Amino acids and proteins
• Ketones
• Carbohydrates and metabolic intermediates
• Aldehydes
• Carbohydrates and metabolic intermediates

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Introduction

• Alcohols were first encountered back in Unit 2
• Alcohols comprise a hydroxyl group (-OH) attached
  to an alkane-type carbon atom.

4
Introduction

• Ethers
• Ethers have an oxygen attached to two alkane-type
  carbon atoms.

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Introduction

• Sulfur containing functional groups
• Sulfur, like oxygen, is a Group VIA element
• Sulfur forms functional groups which are
  analogous to some of the groups formed by oxygen.

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Introduction

• Thiol
• Thiols look similar to alcohols and comprise a
  sulfhydryl (also called mercaptan) group (-SH)
  bonded to an alkane-type carbon.

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Introduction

• Sulfides
• Sulfides look similar to ethers and contain a
  sulfur atom that is bonded to two alkane-type
  carbon atoms.

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Introduction

• Disulfides
• Disulfides look similar to a sulfide, but contain
  two sulfur atoms that are bonded to each other
  and to two alkane-type carbon atoms.

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Introduction

• Ketones
• Ketones are a carbonyl containing functional
  group in which the carbonyl carbon is bonded to
  two other carbon atoms.

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Introduction

• Ketones in the news Diacetyl
• http//www.usatoday.com/news/health/2007-10-27-dia
  cetyl_N.htm

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Introduction

• Aldehydes
• Aldehydes are a carbonyl containing functional
  group in which the carbonyl carbon is bonded to
  at least one hydrogen atom.

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Question

• Circle and label the functional groups found in
  the following compounds.

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Question

• Circle and label the functional groups found in
  the following compounds.

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Question

• Circle and label the functional groups found in
  the following compounds.

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• The IUPAC rules for naming alcohols
• Find the longest carbon chain containing the
  carbon to which the hydroxyl group is attached.
• Remove the -e ending and replace with -ol
• Number the carbon chain from the end closest to
  the hydroxyl group.
• Identify, name and locate any substituent groups
• If the hydroxyl group is being treated as a
  substituent group, refer to it as a hydroxyl
  group.

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• Examples of alcohol names

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• The IUPAC rules for naming thiols
• Find the longest carbon chain containing the
  carbon to which the sulfhydryl group is attached.
• Add the ending -thiol, without removing the
  -e
• Number the carbon chain from the end closest to
  the sulfhydryl group.
• Identify, name and locate any substituent groups

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• Examples of thiol names

(Common names are shown in parentheses)
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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• We will not use the IUPAC rules for naming the
  ethers, sulfides and disulfides.
• Instead of using an ending, the substituents
  attached to the oxygen or sulfur will be listed
  in front fo the family name.

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• Examples of ether, sulfide and disulfide names

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Question

• Name the following structures.

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• Alcohols are also labeled according to the number
  of carbons that are attached to the carbon that
  the hydroxyl group is attached to.
• This will be important for predicting the
  products of oxidation reactions involving
  alcohols.

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• The hydroxyl groups of alcohols are good hydrogen
  bonding donors and acceptors

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Alcohols, Ethers, Thiols, Sulfides and Disulfides

• The other functional groups are not as good at
  forming hydrogen bonds.
• Ethers can only accept hydrogen bonds.
• Sulfur has about the same electronegativity as
  carbon, and therefore, is non-polar.
• This is reflected in the boiling points and
  solubilities of these molecules.

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• In this unit we will be learn many new reactions.
• Pages 346 and 347 in Raymond contains a nice
  summary of all of the reactions that will will
  cover in this unit.

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Alcohols, Ethers, Thiols and Sulfides can be
  prepared from alkyl halides using nucleophilic
  substitution reactions.
• A nucleophile is an electron rich atom or group
  or atoms.
• The halogen atom make a good leaving group.
• The nucleophile attacks that atom to which the
  halogen is attached and the halogen leaves.
• This results in the the nucleophile substituting
  for the leaving group.

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Using nucleophilic substitution to prepare
  alcohols from alkyl halides

The OH- attacks
The Cl- leaves
The OH- attacks
The Br- leaves
The OH- attacks
The I- leaves
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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Using nucleophilic substitution to prepare
  ethers, thiols and sulfides from alkyl halides

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Another way to produce alcohols is the hydration
  of alkenes
• We saw this reaction back in Unit 2

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Reactions Involving Water (Unit 4)

• Hydration
• In the hydration reaction water is also split,
  but instead of being used to split another
  molecule, it is added to another molecule to
  produce a single product.
• The water it is added to either an alkene or
  alkyne
• The hydration of an alkene produces an alcohol.

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Reactions Involving Water (Unit 4)

• Hydration
• This can also be written in shorthand as
• The H below the reaction arrow is used to
  indicate that this is an acid-catalyzed reaction.
• The shorthand is used to emphasize what happens
  to the key reactant.

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Reactions Involving Water (Unit 4)

• Hydration example
• On an earlier slide a reaction from the Citric
  Acid Cycle was shown, which involved the
  dehydrogenation of succinic acid to produce
  fumaric acid.
• The sequent reaction in the Citric Acid Cycle is
  an example of a hydration reaction

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Another way to produce alcohols is the hydration
  of alkenes
• When we looked at hydration reactions back in
  Unit 2 we conveniently picked reactants that
  would only produce one product.
• It is possible to have multiple products in
  hydration reactions.

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Multiple products occur whenever there are a
  different number of hydrogen atoms attached to
  the two carbons double-bonded carbons in the
  alkene.
• Markovnikovs Rule can be used to predict which
  of the two products is predicted to be the major
  product.
• The hydrogen from the water in a hydration
  reaction is added to the double-bonded carbon
  atom that originally carried the most hydrogen
  atoms.
• If you consider hydrogens as a source of wealth,
  this can be more simply stated as
• The rich get richer!

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Preparations of Alcohols ...

• More examples of hydration reactions

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Reactions of Alcohols and Thiols

• Back in Unit 4 we developed several definitions
  for Oxidation-Reduction Reactions.

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Oxidation and Reduction (Unit 4)

• Ways of recognizing oxidation/reduction
  reactions
• Oxidation and reductions always occur together

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Reactions of Alcohols and Thiols

• Back in Unit 7 we saw how the definition loses
  hydrogens could be applied to the oxidation of
  hydroquinones to produce quinones

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Carboxylic Acids Phenols, Other Reactions (Unit
7)

• The oxidation of hydroquinones is also an
  important biological reaction.
• A chemical oxidation of hydroquinones can be
  carried out the oxidizing agent K2Cr2O7
  (potassium dichromate)
• The K2Cr2O7 is not acting as a base to remove 2
  H ions, instead it is removing 2 H atoms.

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Reactions of Alcohols and Thiols

• This same definition can also be applied to the
  oxidation of alcohols by potassium dichromate
  (K2Cr2O7).

The oxidation requires that there are hydrogens
to be removed on the carbon to which the hydroxyl
is bound
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Reactions of Alcohols and Thiols

• Application Breathalyzer(http//science.howstuffw
  orks.com/breathalyzer3.htm

• 1. The sulfuric acid removes the alcohol from
  the air into a liquid solution.
• 2. The alcohol reacts with potassium
  dichromate to produce
• chromium sulfate
• potassium sulfate
• acetic acid
• water
• The silver nitrate is a catalyst,

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Reactions of Alcohols and Thiols

• The oxidation of primary (1) alcohols is a way
  for preparing aldehydes and carboxylic acids.
• The oxidation of secondary (2) alcohols is a way
  for preparing ketones.
• The oxidation of tertiary (3) alcohols does not
  occur because there are not hydrogens attached to
  the carbon to to which the hydroxyl is attached

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Reactions of Alcohols and Thiols
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Reactions of Alcohols and Thiols

• In biological reactions the coenzyme NAD is
  often used as the oxidizing agent.
• The NAD takes the electrons away from alcohols
  to produce aldehydes, carboxylic acids and
  ketones.

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Reactions of Alcohols and Thiols

• Example
• The oxidation of malate to oxaloacetate that
  occurs in the citric acid cycle

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Reactions of Alcohols and Thiols

• Thiols can be oxidized to form disulfides using
  I2 as oxidizing agent
• We will see this oxidation reaction when we
  discuss proteins in Unit 10

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Another reaction that we saw back in Unit 2 was
  the dehydration of alcohols to produce alkenes.
• We saw this reaction back in Unit 2

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Like the complement hydration reaction,
  dehydration can also produce multiple products.

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Multiple products occur whenever there are a
  different number of hydrogen atoms attached to
  the two carbons that are on either side of the
  carbon to which the hydroxyl is attached.
• There is a rule that can be used to predict which
  of the two products is predicted to be the major
  product.
• In a dehydration of an alcohol, the hydrogen will
  be removed from the neighboring carbon atom that
  carries the fewest hydrogen atoms.
• If you consider hydrogens as a source of wealth,
  and since we are removing wealth, this can be
  more simply stated as
• The poor get poor!

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Preparations of Alcohols, Ethers, Thiols and
Sulfides

• Examples of dehydration of alcohols

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Aldehydes and Ketones

• Aldehydes and ketones are carbonyl containing
  functional group.
• They have an array of important roles to play in
  biological chemistry.
• We just saw how they can be prepared from the
  oxidation of primary and secondary alcohols.
• Back in Unit 7, we also saw how they can be
  prepared from the decarboxylation of a-keto acids
  and ß-keto acids.

aldehyde
ketone
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Carboxylic Acids Phenols, Other Reactions (Unit
7)

• The decarboxylation of ß-keto acids produces
  ketones
• The decarboxylation of a-keto acids produces
  aldehydes

(Raymonds answers to problems 10.27b and 10.31
are wrong)
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Aldehydes and Ketones

• The IUPAC rules for naming aldehydes
• Find the longest carbon chain containing the
  carbon to which the hydroxyl group is attached.
• Remove the -e ending and replace with -al
• Number the carbon chain from the carbonyl carbon.
• Identify, name and locate any substituent groups
• Some of the smaller aldehydes have common names
  which are more often used than the IUPAC names.

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Aldehydes and Ketones

• The IUPAC rules for naming ketones
• Find the longest carbon chain containing the
  carbon to which the hydroxyl group is attached.
• Remove the -e ending and replace with -one
• Number the carbon chain from end of the chain
  closest tothe carbonyl carbon.
• Identify, name and locate any substituent groups
• Common names are also used ketones
• The names of the two substituent groups connected
  to the carbonyl carbon are listed and followed by
  the family name ketone.

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Aldehydes and Ketones

• Examples of names for aldehydes and ketones

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Aldehydes and Ketones

• Aldehydes and ketones can serve has hydrogen bond
  acceptors, but not donors.
• This means that they cannot hydrogen bond to
  themselves, and so have much lower boiling points
  than alcohols
• However, they can hydrogen bond to water, so
  small aldehydes and ketones are soluble in water.

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Question

• Draw structures for the following molecules
• 3-Methylheptanal
• 3-Methy-2-pentanone
• Methyl s-butyl ketone

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Oxidation of Aldehydes

• We have already seen how aldehydes and alcohols
  can be oxidized to carboxylic acids with K2Cr2O7

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Oxidation of Aldehydes

• Aldehydes can also be oxidized with the
  copper(II) ion (Cu2)
• This reaction oxidizes aldehydes, but not
  alcohols.
• The Cu2 ion forms a clear blue solution
• The Cu that is produced in the reaction forms an
  orange/red precipitate.

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Oxidation of Aldehydes

• Aldehydes can also be oxidized with the
  copper(II) ion (Cu2)
• The reaction is called the Benedicts reaction,
  and has been used for years in a clinical setting
  to test for the presence of glucose in the urine.

Cu2
Cu
Cu2 Cu
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Reduction of Aldehydes and Ketones

• In Unit 4 we saw how H2 could be used to reduce
  alkenes to alkanes in the hydrogenation reaction.
• Because this reaction involves adding hydrogens
  to a molelcule, it is a reduction reaction.

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Oxidation and Reduction (Unit 4)

• Hydrogenation
• Another type of oxidation/reduction reaction is
  the hydrogenation reaction
• In this example, an alkene is reduced to an
  alkane.
• This is considered reduction, because the
  hydrogen is bringing in additional electrons to
  the molecule.
• The alkane that is produced in this reaction is
  considered saturated because it can no longer
  absorb any more hydrogen atoms.

saturated
unsaturated
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Oxidation and Reduction (Unit 4)

• Often chemist use a shorthand method of writing
  equations like these
• The equation shown on the previous slide can be
  written as follows
• One of the reactants, H2, is placed above the
  reaction arrow
• Technically, this equation is no longer balanced
• The shorthand method of writing a chemical
  equation is used to emphasize what happens to a
  key component of the reaction
• In this case it is the alkene.

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Reduction of Aldehydes and Ketones

• The same reaction can also be used to reduce
  aldehydes and ketones to alcohols

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Reduction of Aldehydes and Ketones

• In biochemistry, NADH H is used instead of H2
• The reduction of a ketone containing steroid by
  the enzyme Hydroxsteroid dehydrogenase.

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Reactions of Alcohols with Aldehydes and Ketones

• Aldehydes and ketones can react with alcohols to
  form hemiacetals, hemiketals, acetals and ketals.
• Theses reactions will become in important in the
  next unit when we talk about carbohydrates.
• This is because carbohydrates are rich in
  aldehydes, ketones and alcohols

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Reactions of Alcohols with Aldehydes and Ketones

• The first reaction, which is similar to the
  reduction of aldehydes and ketones, involves
  adding an alcohol across the carbonyl to form a
  hemiacetal (from aldehydes) or a hemiketal (from
  ketones).

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Reactions of Alcohols with Aldehydes and Ketones

• Hemiacetal and hemiketal formation is catalyzed
  by acids.

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Reactions of Alcohols with Aldehydes and Ketones

• As we will see with the carbohydrates, the
  carbonyl group and the alchohol that react can
  come from the same molecule.
• This will produce a ring molecule.

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Reactions of Alcohols with Aldehydes and Ketones

• A hemiacetal or hemiketal can react with a second
  alcohol to form an acetal or ketal.
• This is a substitution reaction and produces an
  water molecule

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Reactions of Alcohols with Aldehydes and Ketones

• Sometimes the two reactions are combined into a
  single reaction equation

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Question

• Complete the following reaction

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Question

• Draw the structure of the hemiacetal that can
  form from this molecule

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The End