chem 150 unit 8 - organic molecules iii alcohols, thiols, ethers, aldehydes and ketones in this unit...

Chem 150Chem 150Unit 8 - Unit 8 - OrganicOrganic Molecules III Molecules III

Alcohols, Thiols, Ethers, Aldehydes Alcohols, Thiols, Ethers, Aldehydes and Ketonesand Ketones

In this unit we continue surveying some of the In this unit we continue surveying some of the families of organic molecules that play important families of organic molecules that play important

roles in biochemistry; looking both at their roles in biochemistry; looking both at their physical and chemical properties. The Group VIA physical and chemical properties. The Group VIA elements, oxygen and sulfur, typically form two elements, oxygen and sulfur, typically form two covalent bonds to attain a filled valence shell. covalent bonds to attain a filled valence shell. The families that include oxygen and sulfur with The families that include oxygen and sulfur with

two single bonds include two single bonds include alcoholsalcohols C-O-H, C-O-H, ethersethers C- C-O-C, O-C, thiolsthiols C-S-H, C-S-H, sulfidessulfides C-S-C and C-S-C and disulfidesdisulfides C-S-S-C. We will also look at two more important C-S-S-C. We will also look at two more important carbonyl containing functional groups, carbonyl containing functional groups, aldehydesaldehydes

and and ketonesketones..

22

IntroductionIntroduction

The organic groups covered in this Unit all have important biological The organic groups covered in this Unit all have important biological rolesroles• Alcohols Alcohols

• TriglyceridesTriglycerides

• Amino acids and proteinsAmino acids and proteins

• EthersEthers• Biologically active moleculesBiologically active molecules

• ThiolsThiols• Amino acids and proteinsAmino acids and proteins

• OdorantsOdorants

• SulfidesSulfides• Amino acids and proteinsAmino acids and proteins

• KetonesKetones• Carbohydrates and metabolic intermediatesCarbohydrates and metabolic intermediates

• AldehydesAldehydes• Carbohydrates and metabolic intermediatesCarbohydrates and metabolic intermediates

33


Alcohols were first encountered back in Unit 2Alcohols were first encountered back in Unit 2• AlcoholsAlcohols comprise a hydroxyl group (-OH) attached to an comprise a hydroxyl group (-OH) attached to an

alkane-type carbon atom.alkane-type carbon atom.

C O H

44


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

atoms.atoms.

C O C

55


Sulfur containing functional groupsSulfur containing functional groups• Sulfur, like oxygen, is a Group VIA elementSulfur, like oxygen, is a Group VIA element• Sulfur forms functional groups which are analogous to Sulfur forms functional groups which are analogous to

some of the groups formed by oxygen.some of the groups formed by oxygen.

66


ThiolThiol• ThiolsThiols look similar to alcohols and comprise a look similar to alcohols and comprise a sulfhydrylsulfhydryl

(also called (also called mercaptan)mercaptan) group (-SH) bonded to an alkane- group (-SH) bonded to an alkane-type carbon.type carbon.

C S H

77


SulfidesSulfides• SulfidesSulfides look similar to ethers and contain a sulfur atom look similar to ethers and contain a sulfur atom

that is bonded to two alkane-type carbon atoms.that is bonded to two alkane-type carbon atoms.

C S C

88


DisulfidesDisulfides• DisulfidesDisulfides look similar to a sulfide, but contain two sulfur look similar to a sulfide, but contain two sulfur

atoms that are bonded to each other and to two alkane-atoms that are bonded to each other and to two alkane-type carbon atoms.type carbon atoms.

C S CS

99


KetonesKetones• KetonesKetones are a carbonyl containing functional group in are a carbonyl containing functional group in

which the carbonyl carbon is bonded to two other carbon which the carbonyl carbon is bonded to two other carbon atoms.atoms.

C C

O

C

1010


Ketones in the news; DiacetylKetones in the news; Diacetyl• http://www.http://www.usatodayusatoday

.com/news/health/2007-10-27-diacetyl_N..com/news/health/2007-10-27-diacetyl_N.htmhtm

http://www.usatoday.com/news/health/2007-10-27-diacetyl_N.htm




1111


AldehydesAldehydes• AldehydesAldehydes are a carbonyl containing functional group in are a carbonyl containing functional group in

which the carbonyl carbon is bonded to at least one which the carbonyl carbon is bonded to at least one hydrogen atom.hydrogen atom.

C C

O

H

1212

QuestionQuestion

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

alcoholalcoholalcoholalcohol


alkenealkenealkenealkene


etheretheretherether



ketoneketoneketoneketone amineamineamineamine

1313


QuestionQuestion

thiolthiolthiolthiol

thiolthiolthiolthiol

ammoniumammoniumionion

ammoniumammoniumionion

carboxylatecarboxylateionion

carboxylatecarboxylateionion disulfidedisulfidedisulfidedisulfide

sulfidesulfidesulfidesulfide

sulfidesulfidesulfidesulfide


1414


QuestionQuestion


aldehydealdehydealdehydealdehyde ketoneketoneketoneketone


aldehydealdehydealdehydealdehyde

phenolphenolphenolphenol

ketoneketoneketoneketone

1515

Alcohols, Ethers, Thiols, Sulfides and Alcohols, Ethers, Thiols, Sulfides and DisulfidesDisulfides

The IUPAC rules for naming alcoholsThe IUPAC rules for naming alcohols• Find the longest carbon chain containing the carbon to Find the longest carbon chain containing the carbon to

which the hydroxyl group is attached.which the hydroxyl group is attached.• Remove the “-Remove the “-ee” ending and replace with “-” ending and replace with “-olol””• Number the carbon chain from the end closest to the Number the carbon chain from the end closest to the

hydroxyl group.hydroxyl group.• Identify, name and locate any substituent groupsIdentify, name and locate any substituent groups

If the hydroxyl group is being treated as a substituent group, If the hydroxyl group is being treated as a substituent group, refer to it as a “hydroxyl” group.refer to it as a “hydroxyl” group.

1616


Examples of alcohol namesExamples of alcohol names

1717


The IUPAC rules for naming thiolsThe IUPAC rules for naming thiols• Find the longest carbon chain containing the carbon to Find the longest carbon chain containing the carbon to

which the sulfhydryl group is attached.which the sulfhydryl group is attached.• Add the endingAdd the ending “-thiol”“-thiol”, without removing the , without removing the “-e”“-e”• Number the carbon chain from the end closest to the Number the carbon chain from the end closest to the

sulfhydryl group.sulfhydryl group.• Identify, name and locate any substituent groupsIdentify, name and locate any substituent groups

1818


Examples of thiol namesExamples of thiol names

(Common names are shown in parentheses)(Common names are shown in parentheses)(Common names are shown in parentheses)(Common names are shown in parentheses)

1919


We will not use the IUPAC rules for naming the ethers, We will not use the IUPAC rules for naming the ethers, sulfides and disulfides.sulfides and disulfides.• Instead of using an ending, the substituents attached to the Instead of using an ending, the substituents attached to the

oxygen or sulfur will be listed in front fo the family name.oxygen or sulfur will be listed in front fo the family name.

2020


Examples of ether, sulfide and disulfide namesExamples of ether, sulfide and disulfide names

2121

QuestionQuestion

Name the following structures.Name the following structures.

A)A)

B)B)

C)C)

CH3 CH CH CH3

OHCH3

CH3 S CH

CH3

CH3

CH SHCH3

CH3

SH5 S

S CH2 CH3

2222


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

oxidation reactions involving alcohols.oxidation reactions involving alcohols.

CH3 C

OH

H

H

CH3 C

OH

CH3

H

CH3 C

OH

CH3

CH3

primary (1°) secondary (2°) tertiary (3°)

2323


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

2424


The other functional groups are not as good at forming The other functional groups are not as good at forming hydrogen bonds.hydrogen bonds.• Ethers can only accept hydrogen bonds.Ethers can only accept hydrogen bonds.• Sulfur has about the same electronegativity as carbon, and Sulfur has about the same electronegativity as carbon, and

therefore, is non-polar.therefore, is non-polar.

This is reflected in the boiling points and solubilities of these This is reflected in the boiling points and solubilities of these molecules.molecules.

2626

Preparations of Alcohols, Ethers, Thiols and Preparations of Alcohols, Ethers, Thiols and SulfidesSulfides

• In this unit we will be learn many new reactions.In this unit we will be learn many new reactions.

• Pages 346 and 347 in Raymond contains a nice summary Pages 346 and 347 in Raymond contains a nice summary of all of the reactions that will will cover in this unit.of all of the reactions that will will cover in this unit.

2727


Alcohols, Ethers, Thiols and Sulfides can be prepared from Alcohols, Ethers, Thiols and Sulfides can be prepared from alkyl halides using alkyl halides using nucleophilic substitutionnucleophilic substitution reactions. reactions.

• A A nucleophilenucleophile is an electron rich atom or group or atoms. is an electron rich atom or group or atoms.

• The halogen atom make a good The halogen atom make a good leaving groupleaving group..

• The nucleophile “attacks” that atom to which the halogen is The nucleophile “attacks” that atom to which the halogen is attached and the halogen leaves.attached and the halogen leaves.

• This results in the the nucleophile substituting for the This results in the the nucleophile substituting for the leaving group.leaving group.

2828


Using nucleophilic substitution to prepare alcohols from alkyl Using nucleophilic substitution to prepare alcohols from alkyl halides:halides:

The OHThe OH-- attacks attacksThe OHThe OH-- attacks attacks



The IThe I-- leaves leavesThe IThe I-- leaves leaves

The BrThe Br-- leaves leavesThe BrThe Br-- leaves leaves

The ClThe Cl-- leaves leavesThe ClThe Cl-- leaves leaves

2929


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

3030

Preparations of Alcohols, Ethers, Thiols and Sulfides


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

C C + H2OH+

C C

OH H

alkene alcohol

3131

Reactions Involving Water (Unit 4)Reactions Involving Water (Unit 4)

HydrationHydration• In the In the hydration hydration reaction water is also split, but instead of reaction water is also split, but instead of

being used to split another molecule, it is added to another being used to split another molecule, it is added to another molecule to produce a single product.molecule to produce a single product.

• The water it is added to either an alkene or alkyne:The water it is added to either an alkene or alkyne:

• The hydration of an alkene produces an alcohol.The hydration of an alkene produces an alcohol.

C CH

H H

H + H OHacid

catalyst

C CH

H H

H

H OH

ethene(an alkene)

ethanol(an alcohol)

3232


HydrationHydration• This can also be written in shorthand as:This can also be written in shorthand as:• The HThe H++ below the reaction arrow is used to indicate that this is an acid-catalyzed below the reaction arrow is used to indicate that this is an acid-catalyzed

reaction.reaction.

• The shorthand is used to emphasize what happens to the key reactant.The shorthand is used to emphasize what happens to the key reactant.

C CH

H H

H C CH

H H

H

H OH

H2O

H+

ethene(an alkene)

ethanol(an alcohol)

3333


Hydration exampleHydration example• On an earlier slide a reaction from the Citric Acid Cycle On an earlier slide a reaction from the Citric Acid Cycle

was shown, which involved the dehydrogenation of was shown, which involved the dehydrogenation of succinic acid to produce fumaric acid.succinic acid to produce fumaric acid.

• The sequent reaction in the Citric Acid Cycle is an example The sequent reaction in the Citric Acid Cycle is an example of a hydration reaction:of a hydration reaction:

HO C

O

C C

H H

C

O

OH

fumaric acid(an alkene)

H2O

HO C

O

C C

H H

C

O

OH

malic acid(an alcohol)

H OH

3434


Another way to produce Another way to produce alcohols is the alcohols is the hydrationhydration of alkenes of alkenes• When we looked at When we looked at

hydration reactions hydration reactions back in Unit 2 we back in Unit 2 we conveniently picked conveniently picked reactants that would reactants that would only produce one only produce one product.product.

• It is possible to have It is possible to have multiple products in multiple products in hydration reactions.hydration reactions.

3535


Multiple products occur whenever there are a different Multiple products occur whenever there are a different number of hydrogen atoms attached to the two carbons number of hydrogen atoms attached to the two carbons double-bonded carbons in the alkene.double-bonded carbons in the alkene.• Markovnikov’s RuleMarkovnikov’s Rule can be used to predict which of the can be used to predict which of the

two products is predicted to be the major product.two products is predicted to be the major product.-The hydrogen from the water in a hydration reaction is added to the The hydrogen from the water in a hydration reaction is added to the double-bonded carbon atom that originally carried the most hydrogen double-bonded carbon atom that originally carried the most hydrogen atoms.atoms.

• If you consider hydrogens as a source of wealth, this can If you consider hydrogens as a source of wealth, this can be more simply stated asbe more simply stated as

-““The rich get richer!”The rich get richer!”

3636

Preparations of Alcohols ...

Preparations of Alcohols ...

More examples of More examples of hydration reactions:hydration reactions:

3737

Reactions of Alcohols and ThiolsReactions of Alcohols and Thiols

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

3838

Oxidation and Reduction (Unit 4)Oxidation and Reduction (Unit 4)

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

OxidationOxidation ReductionReduction

An atom An atom losesloses electronselectrons

An atom An atom gainsgains electronselectrons

An atom An atom gainsgains a a bond to oxygenbond to oxygen

An atom An atom losesloses a a bond to oxygenbond to oxygen

An atom An atom losesloses a a bond to hydrogenbond to hydrogen

An atom An atom gainsgains a a bond to hydrogenbond to hydrogen

3939


Back in Unit 7 we saw how the definition “loses hydrogens” Back in Unit 7 we saw how the definition “loses hydrogens” could be applied to the oxidation of hydroquinones to produce could be applied to the oxidation of hydroquinones to produce quinonesquinones

4040

Carboxylic Acids & Phenols, Other Reactions Carboxylic Acids & Phenols, Other Reactions (Unit 7)(Unit 7)

The The oxidationoxidation of of hydroquinones is also hydroquinones is also an important biological an important biological reaction.reaction.

• A chemical oxidation A chemical oxidation of hydroquinones of hydroquinones can be carried out can be carried out the oxidizing agent the oxidizing agent KK22CrCr22OO7 7 ((potassium potassium dichromatedichromate))• The KThe K22CrCr22OO77 is not is not

acting as a base to acting as a base to remove 2 Hremove 2 H++ ions, ions, instead it is removing instead it is removing 2 H• atoms.2 H• atoms.

4141


This same definition can also be applied to the oxidation of This same definition can also be applied to the oxidation of alcohols by potassium dichromate (Kalcohols by potassium dichromate (K22CrCr22OO77).).

The oxidation The oxidation requires that requires that there are there are hydrogens to be hydrogens to be removed on the removed on the carbon to which carbon to which the hydroxyl is the hydroxyl is boundbound

The oxidation The oxidation requires that requires that there are there are hydrogens to be hydrogens to be removed on the removed on the carbon to which carbon to which the hydroxyl is the hydroxyl is boundbound

4242


Application: Breathalyzer(Application: Breathalyzer(http://science.http://science.howstuffworkshowstuffworks.com/breathalyzer3..com/breathalyzer3.htmhtm

1. The sulfuric acid removes the alcohol from the air into a liquid solution.

2. The alcohol reacts with potassium dichromate to produce:

1. * chromium sulfate2. * potassium sulfate3. * acetic acid

4. * water The silver nitrate is a catalyst,

1. The sulfuric acid removes the alcohol from the air into a liquid solution.

2. The alcohol reacts with potassium dichromate to produce:

1. * chromium sulfate2. * potassium sulfate3. * acetic acid

4. * water The silver nitrate is a catalyst,

http://science.howstuffworks.com/breathalyzer3.htm




4343


• The oxidation of primary (1°) alcohols is a way for The oxidation of primary (1°) alcohols is a way for preparing preparing aldehydesaldehydes and and carboxylic acidscarboxylic acids..

• The oxidation of secondary (2°) alcohols is a way for The oxidation of secondary (2°) alcohols is a way for preparing preparing ketonesketones..

• The oxidation of tertiary (3°) alcohols does not occur The oxidation of tertiary (3°) alcohols does not occur because there are not hydrogens attached to the carbon to because there are not hydrogens attached to the carbon to to which the hydroxyl is attachedto which the hydroxyl is attached

4444


4545


In biological reactions the In biological reactions the coenzyme NADcoenzyme NAD++ is often used as is often used as the oxidizing agent.the oxidizing agent.• The NADThe NAD++ takes the electrons takes the electrons

away from alcohols to produce away from alcohols to produce aldehydes, carboxylic acids and aldehydes, carboxylic acids and ketones.ketones.

4646


ExampleExample• The oxidation of malate to oxaloacetate that occurs in the The oxidation of malate to oxaloacetate that occurs in the

citric acid cycle:citric acid cycle:

C

C

O O

O H

CH2

C

O O

H

NAD+ NADH + H+ C

C

O O

O

CH2

C

O O

L-malate oxaloacetate

4747


Thiols can be oxidized to form disulfides using IThiols can be oxidized to form disulfides using I22 as oxidizing as oxidizing agentagent

• We will see this oxidation reaction when we discuss We will see this oxidation reaction when we discuss proteins in Unit 10proteins in Unit 10

4848



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

C C + H2OH+

C C

OH H

alkenealcohol

heat

4949



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

5050


Multiple products occur whenever there are a different Multiple products occur whenever there are a different number of hydrogen atoms attached to the two carbons that number of hydrogen atoms attached to the two carbons that are on either side of the carbon to which the hydroxyl is are on either side of the carbon to which the hydroxyl is attached.attached.• There is a rule that can be used to predict which of the two There is a rule that can be used to predict which of the two

products is predicted to be the major product.products is predicted to be the major product.

-In a dehydration of an alcohol, the hydrogen will be removed from the In a dehydration of an alcohol, the hydrogen will be removed from the neighboring carbon atom that carries the fewest hydrogen atoms.neighboring carbon atom that carries the fewest hydrogen atoms.

• If you consider hydrogens as a source of wealth, and since If you consider hydrogens as a source of wealth, and since we are removing wealth, this can be more simply stated aswe are removing wealth, this can be more simply stated as

-““The poor get poor!”The poor get poor!”

5151


Examples of dehydration Examples of dehydration of alcoholsof alcohols

5252

Aldehydes and KetonesAldehydes and Ketones

Aldehydes and ketones are carbonyl containing functional Aldehydes and ketones are carbonyl containing functional group.group.

• They have an array of important roles to play in biological They have an array of important roles to play in biological chemistry.chemistry.

• We just saw how they can be prepared from the oxidation We just saw how they can be prepared from the oxidation of primary and secondary alcohols.of primary and secondary alcohols.

• Back in Unit 7, we also saw how they can be prepared Back in Unit 7, we also saw how they can be prepared from the decarboxylation of α-keto acids and β-keto acids.from the decarboxylation of α-keto acids and β-keto acids.

C C

O

CC C

O

Haldehydealdehydealdehydealdehyde ketoneketoneketoneketone

5353

Carboxylic Acids & Phenols, Other Reactions Carboxylic Acids & Phenols, Other Reactions (Unit 7)(Unit 7)

The decarboxylation of β-keto acids produces The decarboxylation of β-keto acids produces ketonesketones

The decarboxylation of α-keto acids produces The decarboxylation of α-keto acids produces aldehydesaldehydes

(Raymond’s answers to problems 10.27b and 10.31 are wrong)(Raymond’s answers to problems 10.27b and 10.31 are wrong)(Raymond’s answers to problems 10.27b and 10.31 are wrong)(Raymond’s answers to problems 10.27b and 10.31 are wrong)

5454


The IUPAC rules for naming aldehydesThe IUPAC rules for naming aldehydes• Find the longest carbon chain containing the carbon to Find the longest carbon chain containing the carbon to

which the hydroxyl group is attached.which the hydroxyl group is attached.• Remove the “-Remove the “-ee” ending and replace with “-” ending and replace with “-alal””• Number the carbon chain from the carbonyl carbon.Number the carbon chain from the carbonyl carbon.• Identify, name and locate any substituent groupsIdentify, name and locate any substituent groups

Some of the smaller aldehydes have common names which Some of the smaller aldehydes have common names which are more often used than the IUPAC names.are more often used than the IUPAC names.

5555


The IUPAC rules for naming ketonesThe IUPAC rules for naming ketones• Find the longest carbon chain containing the carbon to Find the longest carbon chain containing the carbon to

which the hydroxyl group is attached.which the hydroxyl group is attached.• Remove the “-Remove the “-ee” ending and replace with “-” ending and replace with “-oneone””• Number the carbon chain from end of the chain closest tothe Number the carbon chain from end of the chain closest tothe

carbonyl carbon.carbonyl carbon.• Identify, name and locate any substituent groupsIdentify, name and locate any substituent groups

Common names are also used ketonesCommon names are also used ketones• The names of the two substituent groups connected to the The names of the two substituent groups connected to the

carbonyl carbon are listed and followed by the family name carbonyl carbon are listed and followed by the family name ketone.ketone.

5656


Examples of names for aldehydes and ketonesExamples of names for aldehydes and ketones

5757


Aldehydes and ketones can serve has hydrogen bond Aldehydes and ketones can serve has hydrogen bond acceptors, but not donors.acceptors, but not donors.

• This means that they cannot hydrogen bond to themselves, This means that they cannot hydrogen bond to themselves, and so have much lower boiling points than alcoholsand so have much lower boiling points than alcohols

• However, they can hydrogen bond to water, so small However, they can hydrogen bond to water, so small aldehydes and ketones are soluble in water.aldehydes and ketones are soluble in water.

5959

QuestionQuestion

Draw structures for the following molecules:Draw structures for the following molecules:

A)A) 3-Methylheptanal3-Methylheptanal

B)B) 3-Methy-2-pentanone3-Methy-2-pentanone

C)C) Methyl s-butyl ketoneMethyl s-butyl ketone

6060

Oxidation of AldehydesOxidation of Aldehydes

We have already seen how aldehydes and alcohols can be We have already seen how aldehydes and alcohols can be oxidized to carboxylic acids with Koxidized to carboxylic acids with K22CrCr22OO77

6161


Aldehydes can also be oxidized with the copper(II) ion (CuAldehydes can also be oxidized with the copper(II) ion (Cu2+2+))• This reaction oxidizes aldehydes, but not alcohols.This reaction oxidizes aldehydes, but not alcohols.• The CuThe Cu2+2+ ion forms a clear blue solution ion forms a clear blue solution• The CuThe Cu++ that is produced in the reaction forms an orange/red that is produced in the reaction forms an orange/red

precipitate.precipitate.

6262


Aldehydes can also be Aldehydes can also be oxidized with the copper(II) oxidized with the copper(II) ion (Cuion (Cu2+2+))• The reaction is called the The reaction is called the

Benedict’s reaction, and Benedict’s reaction, and has been used for years has been used for years in a clinical setting to test in a clinical setting to test for the presence of for the presence of glucose in the urine.glucose in the urine.

C

O H

C

C

C

C

CH2 OH

H

H

HO

H OH

H

OH

OH

glucose

CuCu2+2+CuCu2+2+ CuCu++CuCu++CuCu2+2+ + + CuCu++

CuCu2+2+ + + CuCu++

6363

Reduction of Aldehydes and KetonesReduction of Aldehydes and Ketones

In Unit 4 we saw how HIn Unit 4 we saw how H22 could be used to reduce alkenes to could be used to reduce alkenes to alkanes in the alkanes in the hydrogenationhydrogenation reaction. reaction.• Because this reaction involves adding hydrogens to a Because this reaction involves adding hydrogens to a

molelcule, it is a molelcule, it is a reductionreduction reaction. reaction.

6464


HydrogenationHydrogenation• Another type of oxidation/reduction reaction is the Another type of oxidation/reduction reaction is the

hydrogenationhydrogenation reaction: reaction:

• In this example, an alkene is reduced to an alkane.In this example, an alkene is reduced to an alkane.

‣ This is considered reduction, because the hydrogen is bringing in additional This is considered reduction, because the hydrogen is bringing in additional electrons to the molecule.electrons to the molecule.

• The alkane that is produced in this reaction is considered “saturated” because it The alkane that is produced in this reaction is considered “saturated” because it can no longer absorb any more hydrogen atoms.can no longer absorb any more hydrogen atoms.

saturatedsaturatedsaturatedsaturatedunsaturatedunsaturatedunsaturatedunsaturated

C C

H

H

H

H

H2 C

H

H

H

CH

H

H

+platinumcatalyst

6565


Often chemist use a shorthand method of writing equations Often chemist use a shorthand method of writing equations like these:like these:• The equation shown on the previous slide can be written The equation shown on the previous slide can be written

as follows:as follows:

• One of the reactants, HOne of the reactants, H22, is placed above the reaction arrow, is placed above the reaction arrow

‣ Technically, this equation is no longer balancedTechnically, this equation is no longer balanced

• The shorthand method of writing a chemical equation is used to emphasize what The shorthand method of writing a chemical equation is used to emphasize what happens to a key component of the reactionhappens to a key component of the reaction

‣ In this case it is the alkene.In this case it is the alkene.

C CH

H

H

H

H2

PtC

H

H

H

CH

H

H

6666


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

6767


In biochemistry, NADH + HIn biochemistry, NADH + H++ is used instead of H is used instead of H22

• The reduction of a ketone containing steroid by the enzyme The reduction of a ketone containing steroid by the enzyme Hydroxsteroid dehydrogenaseHydroxsteroid dehydrogenase..

6868

Reactions of Alcohols with Aldehydes and Ketones


Aldehydes and ketones Aldehydes and ketones can react with alcohols to can react with alcohols to form hemiacetals, form hemiacetals, hemiketals, acetals and hemiketals, acetals and ketals.ketals.• Theses reactions will Theses reactions will

become in important in become in important in the next unit when we the next unit when we talk about talk about carbohydrates.carbohydrates.

• This is because This is because carbohydrates are rich carbohydrates are rich in aldehydes, ketones in aldehydes, ketones and alcohols and alcohols

C

O H

C

C

C

C

CH2 OH

H

H

HO

H OH

H

OH

OH

glucose

CH2

C

C

C

C

CH2 OH

H

H

HO

O

H

OH

OH

fructose

OH

6969



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

CH2H3C

Propanal(Aldehyde)

C

O

H

O CH2 CH3

H

+

Ethanol(Alcohol)

CH2H3C C

O

H

O CH2 CH3

H

(Hemiacetal)

CH3

Propanone(Ketone)

C

O

CH3

O CH2 CH3

H

+

Ethanol(Alcohol)

CH3 C

O

CH3

O CH2 CH3

H

(Hemiketal)

7070



Hemiacetal and hemiketal formation is catalyzed by acids.Hemiacetal and hemiketal formation is catalyzed by acids.

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

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

molecule:molecule:O CH2 CH3H

Ethanol(Alcohol)

CH2H3C C

O

H

O CH2 CH3

H

(Hemiacetal)

+

Ethanol(Alcohol)

CH3 C

O

CH3

O CH2 CH3

H

(Hemiketal)

+

O CH2 CH3H

CH2 CH3

CH2H3C C

O

H

O CH2 CH3 + H O H

CH2 CH3

CH3 C

O

O CH2 CH3 + H O H

CH3

(Acetal)

(Ketal)

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

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QuestionQuestion

Complete the following reaction:Complete the following reaction:

CH3 CH2 C

O

H + 2 CH3 CH2 OH

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QuestionQuestion

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

CH3 CH CH2 CH2 CH2 C

OH O

H

The EndThe End

chem 150 unit 8 - organic molecules iii alcohols, thiols, ethers, aldehydes and ketones in this unit...

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