20_Lecture....................................ppt

© 2014 Pearson Education, Inc.
Lecture Presentation
Chapter 20
Organic Chemistry
Sherril Soman
Grand Valley State University

• Our sense of smell helps us identify food, people,
and other organisms, and alerts us to dangers such
as polluted air or spoiled food.
• Odorants must be volatile.
• However, many volatile substances have no
scent at all.
• Most common smells are caused by
organic molecules.
• The study of compounds containing carbon
combined with one or more of the elements
hydrogen, nitrogen, oxygen, and sulfur, including
their properties and their reactions, is known as
organic chemistry.
Fragrances and Odors

What Is Organic Chemistry?
• Organic chemistry is a branch of chemistry
that focuses on compounds that contain
carbon.
– Except CO, CO2, carbonates, and carbides
• Even though organic compounds only contain
a few elements, the unique ways carbon
atoms can attach together to form molecules
leads to millions of different organic
compounds.

• Life as we know it is because of organic
chemistry.
• Organic molecules can be very large and
complex.
• It is this complexity of large organic molecules
that allows the complex functions of the cells
to occur.
The Chemistry of Life

• Organic compounds are easily decomposed
into simpler substances by heating, but
inorganic substances are not.
• Inorganic compounds were readily
synthesized in the lab, but synthesis of
organic compounds in the lab is hard.
Differences Between Organic and Inorganic
Compounds

• Organic compounds tend to be molecular.
• They are mainly composed of just six
nonmetallic elements.
– C, H, O, N, S, and P
• Compounds are found in all three states.
– Solids, liquids, and gases
– Solids tend to have low melting points
• Solubility in water varies depending on which
of the other elements are attached to C and
how many there are.
– CH3OH is miscible with water; C10H21OH is
insoluble.
What’s Special About Organic Compounds?

• Carbon atoms can do some unique things
that other atoms cannot.
• Carbon can bond to as many as four
other atoms.
• Bonds to carbon are very strong and
nonreactive.
What’s So Special About Carbon?

• Carbon atoms can attach together in
long chains.
• Carbon atoms can attach together to
form rings.
• Carbon atoms can form single, double,
or triple bonds.
What’s So Special About Carbon?

• Hydrocarbons contain only C and H.
– Aliphatic or aromatic
• Insoluble in water
– No polar bonds to attract water molecules
• Aliphatic hydrocarbons
– Saturated or unsaturated aliphatics
• Saturated = alkanes; unsaturated = alkenes or
alkynes
– May be chains or rings
– Chains may be straight or branched.
• Aromatic hydrocarbons
Hydrocarbons

• Molecular formulas show the kinds of
atoms in the molecule, but they do not
show how they are attached.
• Structural formulas show you the
attachment pattern in the molecule.
• Models not only show you the attachment
pattern, but give you an idea about the
shape of the molecule.
Formulas

• Attached atoms listed in order
– Central atom with attached atoms
• Follow normal bonding patterns
– Use to determine position of multiple bonds
• () used to indicate more than one identical
group attached to same previous central atom
– Unless () group is listed first, in which case
attached to next central atom
Condensed Structural Formulas

Uses of Hydrocarbons

Physical Properties of Aliphatic
Hydrocarbons
• Boiling points and melting points increase
as the size of the molecule increases.
– Nonpolar molecules
– Main attractive forces are dispersion forces
• Less dense than water
• Insoluble in water

Saturated Hydrocarbons
• A saturated hydrocarbon has all C─C
single bonds.
– It is saturated with hydrogens.
• Saturated aliphatic hydrocarbons are called
alkanes.
• Chain alkanes have the general
formula CnH2n+2.
• Ring alkanes have all C─C single bonds, but
have fewer hydrogens than a chain with the
same number of carbons.

• Unsaturated hydrocarbons have one or more
C═C double bonds or C≡C triple bonds.
• Unsaturated aliphatic hydrocarbons that
contain C═C are called alkenes.
– The general formula of a monounsaturated chain alkene
is CnH2n.
– Remove two more H for each additional double bond.
• Unsaturated aliphatic hydrocarbons that
contain C≡C are called alkynes.
– The general formula of an alkyne with one triple bond
is CnH2n−2.
– Remove four more H for each additional triple bond.
Unsaturated Hydrocarbons

Aromatic Hydrocarbons
• Aromatic hydrocarbons contain a ring
structure that seems to have C═C, but
doesn’t behave that way.
• The most prevalent example is benzene.
– C6H6
– Other compounds have the benzene ring
with other groups substituted for some of the
hydrogens.

• Each angle, and beginning and end,
represent a C atom.
• H omitted on C
– Included on functional groups
• Multiple bonds indicated
– Double line is double bond; triple line is
triple bond
Carbon Skeleton Formulas

Formulas

• Isomers are different molecules with the
same molecular formula.
• Structural isomers are isomers that
have a different pattern of atom
attachment.
– Also known as constitutional isomers
• Stereoisomers are isomers with the
same pattern of atom attachments, but
the atoms have a different spatial
orientation.
Isomerism

Butane, BP = 0 °C Isobutane, BP = −12 °C
Structural Isomers of C4H10

Rotation about a Bond Is Not Isomerism

Possible Structural Isomers

Stereoisomers
• Stereoisomers are different molecules
whose atoms are connected in the same
order, but with a different spatial direction.
• Optical isomers are stereoisomers that
are nonsuperimposable mirror images of
each other.
• Geometric isomers are stereoisomers
that are not optical isomers.

Nonsuperimposable Mirror Images
The mirror image cannot be rotated so all its atoms
align with the same atoms of the original molecule.

• Any molecule with a nonsuperimposable
mirror image is said to be chiral.
• Any carbon with four different substituents
will be a chiral center.
• A pair of nonsuperimposable mirror images
are called a pair of enantiomers.
Chirality

Optical Isomers of 3-Methylhexane

• Light that has been filtered so that only
those waves traveling in a single plane are
allowed through
Plane Polarized Light

• Enantiomers have all the same physical
properties except one—the direction they
rotate the plane of plane-polarized light
– Each one of the enantiomers will rotate the plane the
same amount, but in opposite directions.
– Dextrorotatory = rotates the plane to the right
– Levorotatory = rotates the plane to the left
Optical Activity

Mixtures of Enantiomers
• An equimolar mixture of a pair of
enantiomers is called a racemic mixture.
• Because half the molecules are rotating the
plane to the left and the other half are
rotating it to the right, the rotations cancel,
and the racemic mixture does not rotate
the plane.
• If the mixture is nonracemic, the amount of
rotation can be used to determine the
percentages of each enantiomer in the
mixture.

Chemical Behavior of Enantiomers
• A pair of enantiomers will have the same
chemical reactivity in a nonchiral
environment.
• But in a chiral environment they may exhibit
different behaviors.
– Enzyme selection of one enantiomer of a pair

• Also know as paraffins
• Aliphatic
• General formula CnH2n+2 for chains
• Very unreactive
• Come in chains or/and rings
– CH3 groups at ends of chains, CH2 groups in
the middle
• Saturated
• Branched or unbranched
Alkanes

Physical Properties of n–Alkanes

• Each name consists of three parts
– Prefix
• Indicates position, number, and type of branches
• Indicates position, number, and type of each
functional group
– Parent
• Indicates the length of the longest carbon chain or ring
– Suffix
• Indicates the type of hydrocarbon
o -ane, -ene, -yne
• Certain functional groups
Naming

1. Find the longest continuous carbon chain.
2. Number the chain from end closest to a branch.
− If first branches are equal distance, use next
substituent
3. Name branches as alkyl groups.
− Locate each branch by preceding its name with
the carbon number on the chain.
4. List branches alphabetically.
− Do not count n-, sec-, t-, count iso
5. Use prefix if more than one of same group present.
− “Di-,” “tri-,” “tetra-,” “penta-,” “hexa-”
− Do not count in alphabetizing
Naming Alkanes

Prefixes

Alkyl Groups

• Also known as olefins
• Aliphatic, unsaturated
– C═C double bonds
• Formula for one double bond = CnH2n.
– Subtract 2 H from alkane for each
double bond.
• Trigonal shape around C
– Flat
• Polyunsaturated = many double bonds
Alkenes

Alkenes
ethene = ethylene
propene = propylene
Produced by ripening fruit
C C
H
H H
H
C C
H
H CH3
H
Used to make polyethylene Used to make polypropylene

• Pi bond electrons not held as tight as
sigma; therefore, alkenes are more
polarizable than alkanes.
• Cis generally more polar than trans
• Trans lower boiling point
• More carbon groups attached to the double
bond = higher boiling point.
– For equal numbers of C
• Densities similar to alkanes
• Trans higher melting point than cis
– Molecules are more symmetrical and pack better.
Physical Properties of Alkenes

• Also known as acetylenes
• Aliphatic, unsaturated
• CC triple bond
• Formula for one triple bond = CnH2n − 2.
– Subtract 4 H from alkane for each triple bond.
• Linear shape
• Internal alkynes have both triple bond
carbons attached to C.
• Terminal alkynes have one carbon
attached to H.
Alkynes

Alkynes
Used in welding torches
Ethyne = acetylene

Physical Properties of Alkynes
• Higher boiling points than similar sized
alkenes
– Similar size = same number of carbons
– More pi bond = more polarization = higher boiling point
• Slightly higher densities than similar alkenes
• There are no alkyne cis or trans isomers.
• Internal alkynes have higher boiling points
than terminal alkynes.
– With the same number of C

• Change suffix on main name from -ane to
-ene for base name of alkene, or to -yne
for the base name of the alkyne.
• Number chain from end closest to
multiple bond.
• Number in front of main name indicates
first carbon of multiple bond.
Naming Alkenes and Alkynes

Geometric Isomerism
• Because the rotation around a double bond
is highly restricted, you will have different
molecules if groups have different spatial
orientation about the double bond.
– Stereoisomers
• This is often called cis–trans isomerism.
• When groups on the doubly bonded carbons
are cis, they are on the same side of the
double bond.
• When groups on the doubly bonded carbons
are trans, they are on opposite sides.

Cis–Trans Isomerism

Reactions of Hydrocarbons
• All hydrocarbons undergo combustion.
• Combustion is always exothermic.
– About 90% of U.S. energy generated by
combustion
CH3CH2CH3(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)
CH2═CHCH2CH3(g) + 6 O2(g) → 4 CO2(g) + 4 H2O(g)
CH≡CCH3(g) + 4 O2(g) → 3 CO2(g) + 2 H2O(g)

Chemical Energy
• Burning hydrocarbons releases heat
and light energy.
– Combustion
• Alkane + oxygen  carbon dioxide
+ water
• Larger alkane, more heat released

• Substitution
– Replace H with a halogen atom.
– Initiated by addition of energy in the form of heat
or ultraviolet light
• To start breaking bonds
– Generally get multiple products with multiple
substitutions
– Methane + chlorine  chloromethane + HCl
Alkane Reactions

Alkene and Alkyne Reactions: Addition
• Adding a molecule across the multiple bond
• Hydrogenation = adding H2
– Converts unsaturated molecule to saturated
– Alkene or alkyne + H2 → alkane
– Generally requires a catalyst
• Halogenation = adding X2
• Hydrohalogenation = adding HX
– HX is polar.
– When adding a polar reagent to a double or triple
bond, the positive part attaches to the carbon with the
most H’s.

Addition Reactions

Aromatic Hydrocarbons
• Contain benzene ring structure
• Even though they are often drawn with
C═C, they do not behave like alkenes.

Resonance Hybrid
• The true structure of benzene is a
resonance hybrid of two structures.

• (Name of substituent)benzene
– Halogen substituent = change ending to “o”
• Or name of a common derivative
Naming Monosubstituted Benzene
Derivatives

Naming Benzene as a Substituent
• When the benzene ring is not the base
name, it is called a phenyl group.

• Number the ring starting at attachment for
first substituent, and then move toward the
second.
– Order substituents alphabetically.
– Use “di-” if both substituents are the same.
Naming Disubstituted: Benzene Derivatives

• Alternatively, use relative position prefix.
– Ortho- = 1,2; meta- = 1,3; para- = 1,4
2-chlorotoluene
ortho-chlorotoluene
o-chlorotoluene
3-chlorotoluene
meta-chlorotoluene
m-chlorotoluene
4-chlorotoluene
para-chlorotoluene
p-chlorotoluene
Naming Disubstituted: Benzene Derivatives

• Contain multiple benzene rings fused
together
– Fusing = sharing a common bond
Polycyclic Aromatic Hydrocarbons

• Other organic compounds are hydrocarbons
in which functional groups have been
substituted for hydrogens.
• A functional group is a group of atoms that
shows a characteristic influence on the
properties of the molecule.
– Generally, the reactions that a compound will
perform are determined by what functional
groups it has.
– Because the kind of hydrocarbon chain is
irrelevant to the reactions, it may be indicated by
the general symbol.
Functional Groups

• R—OH
• Ethanol = CH3CH2OH
– Grain alcohol = fermentation of sugars
in grains
– Alcoholic beverages
• Proof number = 2 times percentage of
alcohol
– Gasohol
• Isopropyl alcohol = (CH3)2CHOH
– 2-propanol
– Rubbing alcohol
– Poisonous
• Methanol = CH3OH
– Wood alcohol = thermolysis of wood
– Paint solvent
– Poisonous
Alcohols

• Main chain contains OH.
• Number main chain from end closest to OH.
• Give base name -ol ending and place
number of C on chain where OH attached
in front.
• Name as hydroxy group if higher
precedence group present.
Naming Alcohols

Nucleophilic substitution
CH3─OH + HCl  CH3Cl + H2O
Acid catalyzed elimination (dehydration)
CH3─ CH2OH  CH2═CH2 + H2O
H2SO4
Reactions of Alcohols

Reactions of Alcohols
Oxidation
CH3CH2OH  CH3CHO  CH3COOH
−2 H −2 H
A common oxidizing agent is Na2Cr2O7.
Alcohols with very active metals
2 CH3─OH + 2 K  2 CH3O−
K+
+ H2

• Contain the carbonyl group
– Aldehydes = at least 1 side H
– Ketones = both sides R groups
• Many aldehydes and ketones
have pleasant tastes and aromas.
• Some are pheromones.
• Formaldehyde = H2C=O
– Pungent gas
– Formalin = a preservative
– Wood smoke, carcinogenic
• Acetone = CH3C(=O)CH3
– Nail-polish remover
Aldehydes and Ketones

• Acetophenone = pistachio
• Carvone = spearmint
• Ionone = raspberries
• Muscone = musk
Ketone Odors and Flavors

• Main chain contains C═O.
– Unless COOH present
• Number main chain from end closest to C═O.
• For aldehydes, give base name -al ending.
– Always on C1
• For ketones, give base name -one ending and place
number of C on chain where C═O attached in front.
Naming Aldehydes and Ketones

• Aldehydes and ketones are generally
synthesized by the oxidation of alcohols.
• Therefore, reduction of an aldehyde or
ketone results in an alcohol.
• Common reducing agents are H2 with a Ni
catalyst, NaBH4, and LiAlH4.
Reactions

• Aldehydes and ketones are generally
synthesized by the oxidation of alcohols.
• Therefore, reduction of an aldehyde or ketone
results in an alcohol.
• Common reducing agents are H2 with a Ni
catalyst, NaBH4, and LiAlH4.
Reactions

Carbonyl Group
C═O group is highly polar.
Many reactions involve addition across C═O,
with positive part attached to O.

Addition to C═O
Polar molecules add across the
C═O, with the positive part attaching
to O.
 −

• RCOOH
• Sour tasting
• Weak acids
• Citric acid
Found in citrus fruit
• Ethanoic acid = acetic acid
Vinegar
• Methanoic acid = formic acid
Insect bites and stings
Carboxylic Acids

Synthesis of Carboxylic Acids
• Made by the oxidation of aldehydes and
alcohols.

• Carboxylic acid group always on end of
main chain
– Has highest naming precedence of functional
groups
• C of group always C1
– Position not indicated in name
• Change ending to -oic acid
Naming Carboxylic Acids

Examples of Naming Carboxylic Acids

• R—COO—R
• Sweet odor
• Made by reacting carboxylic acid with an alcohol
RaCOOH + RbOH R
⇔ aCOORb + H2O
Esters

• Carboxylic acid group always on end of
main chain
– Unless carboxylic acid group present
• C of ester group on C1
– Position not indicated in name
• Begin name with alkyl group attached to O.
• Name main chain with -oate ending.
Naming Esters

• A condensation reaction is any organic
reaction driven by the removal of a small
molecule, such as water.
• Esters are made by the condensation
reaction between a carboxylic acid and an
alcohol.
 The reaction is acid catalyzed.
Condensation Reactions

• Acid anhydrides are made by the
condensation reaction between to
carboxylic acid molecules.
 The reaction is driven by heat.

Synthesis of Aspirin
(Acetylsalicylic Acid)

Ethers
• Ethers have the general formula ROR.
• The two R groups may be different or
identical.

Ethers
• Diethyl ether is the most common ether.
• It is useful as a laboratory solvent and can
dissolve many organic compounds.
• It has a low boiling point.

• N containing organic molecules
• Very bad smelling
• Form when proteins decompose
• Organic bases
• Name alkyl groups attached to the N, then
add -amine to the end.
Amines

• Many amines are biologically active.
– Dopamine – a neurotransmitter
– Epinephrine – an adrenal hormone
– Pyridoxine – vitamin B6
• Alkaloids are plant products that are
alkaline and biologically active.
– Toxic
– Coniine from hemlock
– Cocaine from coca leaves
– Nicotine from tobacco leaves
– Mescaline from peyote cactus
– Morphine from opium poppies
Amines

Amine Reactions
• Weak bases
– React with strong acids to form ammonium salts
RNH2 + HCl → RNH3
+
Cl−
• React with carboxylic acids in a
condensation reaction to form amides
RCOOH + H—NHR‘ RCONHR
⇔ ’ + H2O

• Polymers are very large molecules made by
repeated linking together of small molecules.
– Monomers
Polymers

• Natural polymers are polymers found in both
the living and nonliving environment.
• Modified natural polymers are natural
polymers that have been chemically altered.
• Synthetic polymers are polymers made in a
lab from one, two, or three small molecules
linked in a repeating pattern.
– Plastics, elastomers (rubber), fabrics, adhesives
• Composites are materials made of polymers
mixed with various additives.
– Additives such as graphite, glass, metallic flakes
Polymers

• Polysaccharides – polymers made of repeating small
sugar molecule units
– Cellulose (cotton)
– Starch
• Proteins – polymers made of repeating amino acid units
• Nucleic acids (DNA) – polymers made of repeating
nucleotide units
• Natural latex rubber – polyisoprene
• Shellac – a resin secreted by lac bugs
• Gutta-percha – a polyisoprene latex from the sap of the
gutta-percha plant
– Used to fill space for root canal
• Amber, lignin, pine rosin – resins from trees
• Asphalt – polymeric petroleum
Natural Polymers

• Cellulose acetate – an ester of cellulose and acetic acid
– Rayon
– Film
• Vulcanized rubber – latex rubber hardened by cross-
linking with sulfur
• Nitrocellulose – an ester of cellulose with nitric acid
– Gun cotton
– Celluloid
• Ping-Pong™ balls
• Casein – a polymer of the protein casein made by
treating cow’s milk with acid
– Buttons, moldings, adhesives
Modified Natural Polymers

Polymerization
• Polymerization is the process of linking the
monomer units together.
• There are two processes by which
polymerization may proceed—addition
polymerization and condensation
polymerization.
• Monomer units may link head to tail, or head
to head, or tail to tail during polymerization.
– Head to tail most common
– Regular pattern gives stronger attractions between
chains than random arrangements

• Monomers add to the growing chain in
such a manner that all the atoms in the
original monomer wind up in the chain.
– No other side products formed; no atoms
eliminated
• First monomer must “open” to start
reaction.
– Done with heat, or the addition of an initiator
• The process is a chain reaction.
– Each added unit ready to add another
Addition Polymerization

Condensation Polymerization
• Monomer units are joined by removing
small molecules from the combining units.
– Polyesters, polyamides lose water
• No initiator is needed.
• The process is a chain reaction.
• Each monomer has two reactive ends, so
the chain can grow in two directions.

• Transparent or translucent
• Chemical resistance
• Thermal and electrical insulators
• Low density
• Varying strengths
– Kevlar
• Mold or extrude
• Elasticity
– Regain original shape if quick stress applied
• Foamed
• Tend to soften when heated, rather than
quickly melt
Characteristics of Plastics

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