Transcript Ch.14

Organic Compounds
containing Oxygen, Halogen,
or Sulfur
Alcohols, Ethers, Alkyl
Halides & Thiols
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ROH
ROR
RX
RSH
• All of these compounds contain a carbon atom
that is singly bonded to a heteroatom (other than H or C)!
• Alcohols & ethers can be considered organic
derivatives of water
• Replacing H(s) with one or two alkyl groups
• HOH; ROH; ROR
Alcohols
• Structural Characteristics
• R-OH
-OH (hydroxyl = functional group)
-OH is bonded to a saturated C atom!
• Classification
• Primary (1˚)
• Secondary (2˚)
• Tertiary (3˚)
C-C-OH
C-C-OH
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C
C
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C-C-OH
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C
Alcohol Nomenclature
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IUPAC
1. Name the longest chain (drop the “e” and
add “ol” at the end) to which -OH is
attached.
2. # the chain from the end nearest the -OH*
(# the position of the -OH group).
3. Name/locate any substituents.
4. For rings, -OH is on C#1.
IUPAC naming examples
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• Ex.: CH3OH
Methanol
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CH3CH2CH2OH 1-propanol
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CH3CHCH3
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OH
2-propanol
3,4-dimethylcyclohexanol
• Alcohols with >1 -OH groups
• Ex.: CH2CH2
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OH OH
1,2-ethanediol
Alcohol Nomenclature
• Common (name “R” as an alkyl group)
• Alkyl group name + alcohol
• Ex.: CH3OH
Methyl alcohol
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CH3CHCH3
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Isopropyl alcohol
OH
• Alcohols with >1 -OH groups
• Ex.:
Important Common Alcohols
• IUPAC
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Methanol
Ethanol
2-propanol
1,2-ethanediol
1,2-propanediol
1,2,3-propanetriol
For survival in northern winters,
many fish and insects produce
large amounts of glycerol that
dissolve in their blood, thereby
lowering the freezing point.
• Common
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Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Ethylene glycol
Propylene glycol
Glycerol (glycerin)
How
does %
relate to
“proof”?
Constitutional Isomerism
• Positional
• Ex.: butanol
1-butanol
2-butanol
• Skeletal
• Ex.: butanol
2-butanol
sec-butyl alcohol
2-methyl-2-propanol
tert-butyl alcohol
Physical Properties of Alcohols
• Alcohols have both Polar & Nonpolar
character!
(-OH) (alkyl)
• Properties are determined by which portion
dominates
• Short chain (<6) - polar end dominates
• Long chain (6+) - nonpolar end dominates
• BP increases with increasing # of C atoms
• Effect of London Dispersion Forces
• Water solubility
• Short chain - soluble
• Long chain - insoluble
• Alcohols can Hydrogen bond
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(better with small chain alcohols)
affects BP & Solubility in Water
• Alkanes cannot Hydrogen bond
• (a) The polar hydroxyl functional group dominates the
physical properties of methanol.
• (b) Conversely, the nonpolar portion of 1- octanol
dominates its physical properties.
Chemical Reactions of Alcohols
• Combustion
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CH3OH +
O2 -->
CO2 +
H2O
• Two types of Dehydration!
• Intramolecular Alcohol dehydration
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Conditions: 180˚C and H2SO4 catalyst
Result: formation of alkene (elimination/condensation rxn)
Ex.: C-C-OH ----> C=C + H2O
Ex.: 2-butanol -->
• Zaitsev’s rule: major product
is alkene w/ greatest #
of alkyl groups
Chemical Reactions of Alcohols
• Intermolecular Alcohol dehydration
• Conditions: 140˚C (lower temp!) and H2SO4
catalyst
• Result: formation of ether (R-O-R)
(condensation rxn)
• Ex.: C-OH + HO-C ----> C-O-C + H2O
Halogenation Reactions
• R-C-OH + X2 ----> R-C-X2 + H2O
• Not a particularly common reaction, however
Oxidation Reactions
• 1˚ alcohol ---> aldehyde ---> carboxylic
acid
• 2˚ alcohol ---> ketone
• 3˚ alcohol ---> No Reaction!
The oxidation of ethanol
is the basis for the
“breathalyzer test.”
• Oxidation results in an increase in the
number of C-O bonds or a decrease in
the number of C-H bonds.
Preparation of Alcohols
• Alcohols can be prepared in two major ways:
• Alkene hydration
• Ex.: CH2=CH2 + H2O ----> CH3CH2OH
• Addition of H2 to a carbonyl group (-C=O)
• Ex.: Aldehyde + H2 ----> 1˚ alcohol
Ketone + H2 ----> 2˚ alcohol
Phenols
• Structural Characteristics
• -OH is attached to a C that is part of an
aromatic ring.
• Ar-OH
Nomenclature of Phenols
• Phenol = “phenyl” + “alcohol”
• IUPAC rules are same as for benzene
derivatives. Parent ring is “phenol”.
• Ex.:
Physical & Chemical Properties of
Phenols
• Flammable, like alcohols
• Phenols cannot be dehydrated.
• Oxidation occurs only with strong
oxidizing agents.
• Halogenation
• Weak acids in solution (Ka~10-10)
Many commercially
baked goods contain
the antioxidants BHA
and BHT to help
prevent spoilage.
Occurance & Uses of
Phenols
• Antiseptics (but phenol derivatives are much
safer than phenol itself).
• Mouthwashes, Lysol, etc.
• Antioxidant - several phenols are
preferentially oxidized
• Food additives
• Vit. E
• Flavoring agents
• Irritants: poison ivy & poison oak
Nutmeg tree fruit. A phenolic compound,
isoeugenol, is responsible for the odor
associated with nutmeg.
Ethers
• Structural Characteristics
• Functional group = -C-O-C• Remember ascorbic acid?
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R-O-R
R-O-R’
R-O-Ar
Ar-O-Ar
Nomenclature of Ethers
• IUPAC
• Select longest C chain =
base name.
• Change -yl ending of
other group to -oxy. (ie.
Methyl becomes
methoxy)
• Place alkoxy name (w/
locator #) in front of base
chain name
• Ex.: C-C-O-C-C-C-C
• Common
• Name the two alkyl
groups (alpha order)
attached to the O
and add the word
“ether”.
Examples:
Isomerism
• Consitutional
• Partitioning of C
atoms (by O) positional!
• Isomers of individual
alkyl groups
• Ex.: C4 ethers
• Functional Group
Isomers (1st time we
encounter this possibility)
• Consitutional
isomers with different
functional groups
• Ex.: C3 ether and C3
alcohol
Physical & Chemical
Properties
• Physical
• BP = to alkanes; lower
than alcohols
• No H-bonding w/ self
possible
• Water soluble
• Can H-bond w/ water
• NP substances are
generally soluble in
ethers
• Act as anesthetics
• Diethyl ether
• Chemical
• Flammable
• React w/ O2 to form
unstable (explosive)
ccompounds
• Unreactive w/ acids and
oxidizing agents
• Halogenation
• Prepared by intermolecular
dehydration of 1˚ alcohols
Alkyl Halides:
Incoming halogen atom (orange sphere)
replaces a hydrogen atom in the alkane
model.
• Naming:
• Treat halogen atoms like alkyl groups.
• F = fluoro; Cl = chloro; Br = bromo; I = iodo
• Ex.: CH3-CHBr-CHBr-CHI-CH2-CH3
Halogenation Reactions
General equation: RH + X2 → RX + HX
Hydrocarbon + Halogen  Halogenated + acid
(diatomic) hydrocarbon
Ex.
CH4 + Cl2 -->
CH3Cl + HCl
Highly exothermic reaction: can lead to an
explosion
The process can continue to alter the
resulting products as long as the halogen
remains in sufficient quantities to drive
further reactions. (The halogen would be
the __________ reactant.)
Space-filling models of the
four ethyl halides.
Do these molecules act as polar or non-polar?
Chlorofluorocarbons
(CFCs)
• Developed in the 1930's
• Very stable compounds composed of C, F, Cl, & H
• Freon is the tradename:
• Trichlorofluoromethane
• Dichlorodifluoromethane
Trichloro-trifluoroethane
Dichloro-tetrfluoroethane
Chloropentafluoroethane
Safe, non-toxic,
non-flammable
alternative to
dangerous
substances
(e.g. ammonia)
for aerosol-spray
propellants,
refrigerants,
solvents, and
foam-blowing agents
CFCs and refrigeration
CFCs and
propellants
UV radiation in
the stratosphere
The Ozone Layer Chemistry
CFCl3 + UV Light ==> CFCl2 + Cl
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
The chlorine free radical atom
is then able to attack another
ozone molecule
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again ...
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again... thousands of times!
A catalyst!
The ozone destruction process requires conditions
cold enough (-80oC) for stratospheric clouds to form.
Once these stratospheric clouds form the process
can take place, even in warmer conditions
Ozone consumption has been greatly
reduced,
however CFCs may linger for another
150 years in the atmosphere
1997
ozone
hole
2003
ozone
hole
Ozone layer thickness
Thiols = Mercaptans:
sulfhydryl
group (-SH) bonded to a saturated C atom
• Alcohol - R-OH
• C-C-OH (ethanol)
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(ethyl alcohol)
• Thiol - R-SH
• C-C-SH (ethanethiol)
• (ethyl mercaptan)
Properties of Thiols
• Physical
• Low BP
• No H-bonding
• Strong odor
• Skunks (3-methyl-1butanethiol)
• Methanethiol
(additive to natural
gas)
• Morning breath
• Onions (1-propanethiol)
• Chemical
• Oxidation-Reduction
2 thiols <==> Disulfide
• Important in Protein
chemistry
Thioethers - replace the “O” with “S” (R-S-R)
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C-S-C
C-S-C-C-C
Ar-S-C
C=C-S-C
C=C-C-S-C
C=C-C-S-S-C-C=C
• Morning Breath =
Hydrogen sulfide
Methanethiol
Dimethyl sulfide…
• Onions
• Garlic
Disulfides are
important in some
protein structures.
What do you need to know?
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Structural characteristics (know the functional group)
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Alcohol
Phenol
Ether
Sulfur Analogs
Isomers
Nomenclature (the rules for naming the molecules)
• Common & IUPAC
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Physical properties (basic/simple)
• BP; Solubility; Flammability
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Occurrence and uses (common)
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• Natural (ex.: menthol, skunk, nutmeg, clove, garlic, onion)
• Synthetic (ex.: antiseptics, racing fuel, de-icers, antioxidants, anesthetics)
Preparation (what basic reactions produce the molecules)
• Alcohols - alkene hydration; Phenols - benzene hydration
• Ethers - intermolecular alcohol dehydration
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Characteristic reactions of the molecules
• Combustion; dehydration; halogenation; oxidation