Transcript File

Organic Compounds that Contain
Oxygen or Sulfur
Three families of compounds that contain a C atom
singly bonded to O or S are:
1. Alcohols, which contain an OH (hydroxyl) group
2. Ethers, which have two alkyl groups bonded to
an O atom
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Organic Compounds that Contain
Oxygen, Halogen, or Sulfur
3. Alkyl halides, which contain a halogen atom,
(X= F, Cl, Br, or I) bonded to a tetrahedral carbon.
4. Thiols, which contain a SH (sulfhydryl) group.
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Organic Compounds that Contain
Oxygen, Alkyl Halides, or Sulfur
Two families of compounds that contain a carbonyl
group C=O:
1. Aldehydes, which have at least one H atom
bonded to the carbonyl carbon.
2. Ketones, which have two alkyl groups bonded to
the carbonyl carbon.
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Structure and Properties of Alcohols
• Alcohols contain a hydroxyl (OH) group.
• Alcohols are classified by the number of C atoms
bonded to the C with the OH group.
A primary (1o) alcohol has
an OH group on a C bonded
only to 1 C atom.
1o
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Structure and Properties of Alcohols
A secondary (2o) alcohol has
an OH group on a C bonded
only to 2 C atoms.
2o
3o
A tertiary (3o) alcohol has
an OH group on a C bonded
only to 3 C atoms.
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Structure and Properties of Alcohols
• An alcohol (ROH) contains an O atom with a bent
shape like H2O and a bond angle similar to a
tetrahedral.
• Alcohols have an H atom bonded to an O atom,
making them capable of intermolecular hydrogen
bonding.
• This gives alcohols much stronger
intermolecular forces than hydrocarbons.
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Structure and Properties of Alcohols
• As a result, alcohols have higher boiling and melting
points than hydrocarbons of comparable molecular
weight and shape.
melting point: -138 ºC
boiling point: -0.5 ºC
melting point: -127 ºC
boiling point: 97 ºC
stronger intermolecular forces
higher boiling and melting point
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Structure and Properties of Alcohols
• Alcohols are soluble in organic solvents.
• Low molecular weight alcohols (6 Cs or less)
are soluble in water.
• Higher molecular weight alcohols (6 Cs or more)
are not soluble in water.
2 Cs in chain
water soluble
8 Cs in chain
water insoluble
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Nomenclature of Alcohols
In the IUPAC system, alcohols are identified
by the suffix -ol.
To name an alcohol:
• Find the longest carbon chain containing the
carbon bonded to the OH group.
• Number the carbon chain to give the OH group
the lower number, and apply all other rules of
nomenclature.
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Nomenclature of Alcohols
Sample Problem 12.2
Give the IUPAC name of the following alcohol.
Step [1]
Find the longest carbon chain containing the
C bonded to the OH group.
5 Cs in longest chain
pentane ----> pentanol
• Change the –e ending of
the parent alkane to the
suffix –ol.
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Nomenclature of Alcohols
Step [2]
Number the carbon chain to give the OH group
the lower number, and apply all other rules
of nomenclature.
1-pentanol
Answer
3,3-dimethyl-1-pentanol
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Nomenclature of Alcohols
• When an OH group is bonded to a ring, the OH
is automatically on C1.
• The “1” is usually omitted from the name.
• The ring is then numbered to give the next
substituent the lower number.
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Structure and Properties of Ethers
• Ethers (ROR) have two alkyl groups bonded to
an O atom.
• The O atom of an ether has a bent shape like
H2O and a bond angle similar to a tetrahedral.
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Naming Ethers
Simple ethers are usually assigned common names:
• Name both alkyl groups bonded to the O atom.
• Arrange these names alphabetically.
• Finally, add the word “ether” to the end.
• For identical alkyl groups, add the prefix di-.
CH3 O
methyl
CH2CH3
ethyl
ethyl methyl ether
CH3CH2 O
ethyl
CH2CH3
ethyl
diethyl ether
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Structure and Properties of Ethers
Physical Properties
• Ether has two polar C—O bonds with a bent
shape, therefore it has a net dipole.
• Ether does not contain an H atom bonded to an
O atom, so ether cannot form intermolecular
hydrogen bonds.
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Structure and Properties of Ethers
Physical Properties
These facts give ethers:
• stronger intermolecular forces than alkanes.
• weaker intermolecular forces than alcohols.
As a result, ethers of comparable size and shape
tend to have:
• higher melting and boiling points than hydrocarbons.
• lower melting and boiling points than alcohols.
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Structure and Properties of Ethers
Physical Properties
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Structure and Properties of Ethers
Physical Properties
• Ethers are soluble in organic solvents.
• Low molecular weight ethers (5 Cs or less) are
soluble in water, as water can hydrogen bond to
the ether’s O atom.
• Higher molecular weight ethers (6 Cs or more)
are not soluble in water.
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Focus on Health & Medicine
Ethers as Anesthetics
• A general anesthetic is a drug that interferes with
nerve transmission in the brain, resulting in a loss
of consciousness and the sensation of pain.
• Diethyl ether was first demonstrated as an
anesthetic in the nineteenth century.
• Modern variations include the three ethers below:
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Reactions of Alcohols
Dehydration
• Dehydration is the loss of H2O from a starting
material.
• It occurs when an alcohol is treated with a strong
acid like H2SO4, and forms an alkene product.
• Dehydration is an example of an elimination
reaction, in which parts of the starting material are
“lost” and a multiple bond is formed.
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Reactions of Alcohols
Dehydration
• Examples:
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Reactions of Alcohols
Oxidation
Oxidation results in a(n):
• increase in the number of C—O bonds.
• decrease in the number of C—H bonds.
The symbol [O] indicates an oxidation reaction.
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Reactions of Alcohols
Oxidation
• Oxidation occurs by replacing the C—H bonds
on the carbon bearing the OH group by C—O
bonds.
• All oxidation products from alcohol starting
materials contain a C=O, a carbonyl group.
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Reactions of Alcohols
Oxidation
• Primary (1o) alcohols first oxidize to aldehydes
(RCHO), replacing 1 C—H with 1 C—O.
• Aldehydes are further oxidized to carboxylic
acids (RCOOH), replacing 1 C—H with 1 C—O.
1o alcohol
(ROH)
aldehyde
(RCHO)
carboxylic acid
(RCOOH)
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Reactions of Alcohols
Oxidation
• Secondary (2o) alcohols are oxidized to ketones
(R2CO) replacing 1 C—H with 1 C—O.
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Reactions of Alcohols
Oxidation
• Tertiary (3o) alcohols have no H atoms on the C
with the OH group, so they are not oxidized.
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Focus on The Human Body
Oxidation and Blood Alcohol Screening
• The oxidation of ethanol with K2Cr2O7 was the
first available method for the routine testing of
alcohol concentration in exhaled air.
• Oxidation with K2Cr2O7 is characterized by a color
change, as the red-orange reagent is reduced to a
green Cr3+ product.
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Focus on Health & Medicine
The Metabolism of Ethanol
• When ethanol is consumed it is quickly absorbed
in the stomach and small intestines.
• In the liver, the enzymes alcohol and aldehyde
dehydrogenase act as oxidizing reagents.
CH3CH—OH
[O]
O
C
CH3
ethanol
[O]
H
acetaldehyde
O
C
CH3
OH
acetic acid
• Consuming more ethanol than can be metabolized
leads to a buildup of acetaldehyde, which is toxic.
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Organic Compounds that Contain
Alkyl Halides
• Alkyl Halides contain a halogen atom
(X= F, Cl, Br, or I) bonded to a tetrahedral carbon.
• Alkyl halides are classified by the number of C
atoms bonded to the C with the halogen.
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Structure and Properties of Alkyl Halides
• Alkyl halides contains a polar C–X bond, but are
incapable of hydrogen bonding.
For an alkyl halide, the…
• boiling point and melting point increase with the
size of the alkyl group due to increased surface area.
• boiling point and melting point increase with the
size of the halogen.
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Structure and Properties of Alkyl Halides
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Nomenclature of Alkyl Halides
HOW TO Name an Alkyl Halide
Example
Give the IUPAC name of the following
alkyl halide:
Step [1]
Find the longest chain containing the
halogen.
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Nomenclature of Alkenes and Alkynes
HOW TO Name an Alkene or Alkyne
Step [2] Apply all other rules of nomenclature.
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Organic Compounds that Contain Sulfur
• Thiols contain a sulfhydryl group (SH) bonded to
a tetrahedral carbon.
• Because S is just below O on the periodic table,
thiols are similar to alcohols.
• Thiols have a bent shape around the S atom.
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Organic Compounds that Contain Sulfur
• However, thiols contain no O—H bonds, so they
are incapable of intermolecular hydrogen bonding.
• This gives thiols lower boiling and melting points
than similar alcohols.
CH3CH2—OH
ethanol
CH3CH2—SH
ethanethiol
bp 78 oC
bp 35 oC
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Organic Compounds that Contain Sulfur
• Thiols have a characteristic foul odor (skunk,
onions, etc.)
• They can be oxidized to disulfides.
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Organic Compounds that Contain Sulfur
• The disulfides can be converted back to thiols
with a reducing agent.
• The symbol for a general reducing agent is [H],
since hydrogen atoms are often added during
reduction.
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Organic Compounds that Contain Sulfur
• To make straight hair curly, the disulfide bonds
holding the hair proteins together are reduced.
• The hair is then turned around curlers, and an
oxidizing agent is applied.
• This re-forms the disulfide bonds in the hair, now
giving it a curly appearance.
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Aldehydes and Ketones
Structure and Properties of Aldehydes and
Ketones
Two families of compounds contain a carbonyl group:
Aldehydes (RCHO)
Ketones (RCOR or R2CO)
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Aldehydes and Ketones
Structure and Properties of Aldehydes
and Ketones
• The carbonyl carbon atom is trigonal planar, with
bond angles of 120o.
• O is more electronegative than C, so the carbonyl
group is polar.
• The carbonyl C is e− rich (δ−) and the carbonyl
O is e− poor (δ+).
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Nomenclature
Naming Aldehydes
To name an aldehyde using the IUPAC system:
• Find the longest chain containing the CHO group.
• Change the “-e” ending of the parent alkane to “-al.”
• Number the chain to put the CHO group at C1, but
omit “1” from the name.
• Apply all other nomenclature rules.
CH3
CH3CHCH C
3 2
CH3
butane  butanal
O
1
H
Answer:
2,3-dimethylbutanal
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Nomenclature
Naming Aldehydes
Common names are used for simple aldehydes;
the names contain the suffix “-aldehyde.”
formaldehyde
acetaldehyde
benzaldehyde
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Nomenclature
Naming Ketones
To name a ketone using the IUPAC system:
• Find the longest chain containing the carbonyl
group.
• Change the “-e” ending of the parent alkane to
“-one.”
• Number the chain to give the carbonyl carbon the
lower number.
• Apply all other nomenclature rules.
O
CH3 C
1
2
pentane  pentanone
CHCH2CH3
CH3
3
Answer:
3-methl-2-pentanone
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Nomenclature
Naming Ketones
• With cyclic ketones, numbering begins at the
carbonyl carbon, “1” is omitted from the name.
• The ring is then numbered clockwise or
counterclockwise to give the first substituent the
lower number.
Sample Problem 12.7
Step [1]
Name the ring.
cyclohexane  cyclohexanone
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Nomenclature
Naming Ketones
Sample Problem 12.7
Step [2]
Number and name the substituents,
making the C=O C1.
1
3
Answer:
3-ethyl-4-methylcyclohexanone
4
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Physical Properties
Aldehydes and ketones have higher boiling points
than similar hydrocarbons because:
• They are polar molecules.
• They have stronger intermolecular forces than
alkanes and alkenes.
CH3CH2CH2CH2CH3
pentane
bp 36 oC
CH3CH2CH2CHO
butanal
bp 76 oC
Increasing boiling point
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Physical Properties
Aldehydes and ketones have lower boiling points
than similar alcohols because:
• They do not have an O—H bond.
• Therefore, they cannot have intermolecular
hydrogen bonding.
• Thus, they have weaker intermolecular forces
than alcohols.
CH3CH2COCH3
2-butanone
bp 80 oC
CH3CH2CH2CH2OH
1-butanol
bp 118 oC
Increasing boiling point
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Physical Properties
• Aldehydes and ketones are soluble in organic
solvents.
• Those molecules with less than 6 Cs are soluble
in both organic solvents and water.
• Those molecules with 6 Cs or more are soluble
in organic solvents, but insoluble in water.
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Focus on Health & Medicine
Interesting Aldehydes and Ketones
Cinnamaldehyde, the major component of
cinnamon bark:
Vanillin, the primary component of the extract of the
vanilla bean:
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Oxidation of Aldehydes
Aldehydes contain a hydrogen atom bonded directly
to the carbonyl carbon; they can be oxidized to
carboxylic acids:
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Reactions of Aldehydes and Ketones
Oxidation of Aldehydes
In oxidation, the aldehyde C—H bond is converted
into a carboxylic acid C—OH bond.
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Reactions of Aldehydes and Ketones
Oxidation of Aldehydes
Ketones cannot be oxidized because there is no
C—H bond.
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Reactions of Aldehydes and Ketones
Oxidation of Aldehydes
Aldehydes can be selectively oxidized in the presence
of other functional groups using the Tollens reagent.
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Looking Glass Chemistry
Molecules and Their Mirror Images
Stereochemistry is the 3-dimensional structure of
compounds.
Stereoisomers differ only in the 3-dimensional
arrangement of atoms.
• The cis and trans examples below are
stereoisomers.
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Molecules and Their Mirror Images
What It Means to be Chiral or Achiral
• Left hands and right hands are mirror images of
each other.
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Molecules and Their Mirror Images
What It Means to be Chiral or Achiral
• Left and right hands are not identical
(nonsuperimposable).
• A molecule that is not superimposable on its mirror
image is chiral.
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Molecules and Their Mirror Images
What It Means to be Chiral or Achiral
• Two socks from a pair are mirror images that are
superimposable.
• A molecule that is superimposable on its mirror
image is achiral.
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Molecules and Their Mirror Images
The Chirality of Molecules
To determine whether a molecule is chiral or achiral
we must examine what groups are bonded to each
carbon atom:
• A chiral molecule has at least one carbon atoms
bonded to four different groups.
• An achiral molecule does not contain a carbon
atom bonded to four different groups.
To superimpose a molecule and its mirror image
you can perform any rotation but you cannot
break bonds.
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Molecules and Their Mirror Images
The Chirality of Molecules
• For CH2BrCl:
• Rotate the
molecule to
align bonds:
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Molecules and Their Mirror Images
The Chirality of Molecules
• For CHBrClF:
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Molecules and Their Mirror Images
The Chirality of Molecules
• The two mirror images of CHBrClF are enantiomers,
mirror images that are not superimposable.
• A molecule that is not superimposable on its mirror
image is a chiral molecule.
• A carbon atom with four different groups like
CHBrClF is called a chirality center.
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Chirality Centers
Locating Chirality Centers
• To locate a chirality center, look at each tetrahedral
C atom in a molecule.
• Look at the four groups—not the four atoms—
bonded to it.
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Chirality Centers
Locating Chirality Centers
• We consider all atoms in a group as a whole unit.
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Chirality Centers
Locating Chirality Centers
• Chirality centers in the examples below are
labeled in red:
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Fischer Projections
A Fischer Projection takes a 3-D tetrahedral shape,
and re-draws it.
• A carbon atom is located at the intersection.
• The horizontal bonds come forward, on the
wedges.
• The vertical bonds go back, on the dashed lines.
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Fischer Projections
• We can draw the cross and Fischer projection
for both enantiomers of 2-butanol:
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Focus on Health & Medicine
Chiral Drugs
• Many drugs are chiral, and often they must interact
with a chiral receptor to be effective.
• One enantiomer of a drug may be effective in
treating a disease whereas its mirror image may be
ineffective.
• One enantiomer may “fit” the chiral receptor
and evoke a specific response.
• Its mirror image may not fit the same receptor,
making it ineffective.
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Focus on Health & Medicine
Chiral Drugs
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Focus on Health & Medicine
Chiral Pain Relievers
• Ibuprofen is an active anti-inflammatory agent
whose enantiomer is inactive, and is sold as a
racemic mixture.
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Focus on Health & Medicine
Parkinson’s Disease and L-Dopa
• L-Dopa, a dopamine precursor, is used to help treat
the dopamine deficient brains of Parkinson’s
patients.
• Dopamine cannot be directly taken by a patient
because it cannot cross the blood-brain barrier.
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