Download Chapter 25 Organic and Biological Chemistry

Chemistry, The Central Science, 11th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 25
Organic and
Biological Chemistry
John D. Bookstaver
St. Charles Community College
Cottleville, MO
Organic and
Biological
Chemistry
© 2009, Prentice-Hall, Inc.
Organic Chemistry
•  Organic chemistry is the chemistry
of carbon compounds.
•  Carbon has the ability to form long
chains.
•  Without this property, large
biomolecules such as proteins,
lipids, carbohydrates, and nucleic
acids could not form.
Organic and
Biological
Chemistry
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Structure of Carbon Compounds
•  There are three hybridization states and
geometries found in organic compounds:
–  sp3 Tetrahedral
–  sp2 Trigonal planar
–  sp Linear
Organic and
Biological
Chemistry
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Hydrocarbons
•  There are four basic
types of hydrocarbons:
–  Alkanes
–  Alkenes
–  Alkynes
–  Aromatic hydrocarbons
Organic and
Biological
Chemistry
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Alkanes
•  Alkanes contain only single bonds.
•  They are also known as saturated hydrocarbons.
–  They are “saturated” with hydrogens.
Organic and
Biological
Chemistry
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Formulas
•  Lewis structures of alkanes look like this.
•  They are also called structural formulas.
•  They are often not convenient, though…
Organic and
Biological
Chemistry
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Formulas
…so more often condensed formulas are used.
Organic and
Biological
Chemistry
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Properties of Alkanes
•  The only van der Waals force is the London
dispersion force.
Organic and
•  The boiling point increases with the length Biological
Chemistry
of the chain.
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Structure of Alkanes
•  Carbons in alkanes are sp3 hybrids.
•  They have a tetrahedral geometry and 109.5°
bond angles.
Organic and
Biological
Chemistry
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Structure of Alkanes
•  There are only σbonds in alkanes.
•  There is free rotation
about the C—C
bonds.
Organic and
Biological
Chemistry
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Isomers
Isomers have the
same molecular
formulas, but the
atoms are
bonded in a
different order.
Organic and
Biological
Chemistry
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Organic Nomenclature
•  There are three parts to a compound name:
–  Base: This tells how many carbons are in the
longest continuous chain.
Organic and
Biological
Chemistry
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Organic Nomenclature
•  There are three parts to a compound name:
–  Base: This tells how many carbons are in the
longest continuous chain.
–  Suffix: This tells what type of compound it is.
Organic and
Biological
Chemistry
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Organic Nomenclature
•  There are three parts to a compound name:
–  Base: This tells how many carbons are in the
longest continuous chain.
–  Suffix: This tells what type of compound it is.
–  Prefix: This tells what groups are attached to the
chain.
Organic and
Biological
Chemistry
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How to Name a Compound
1.  Find the longest chain in
the molecule.
2.  Number the chain from
the end nearest the first
substituent encountered.
3.  List the substituents as a
prefix along with the
number(s) of the
carbon(s) to which they
are attached.
Organic and
Biological
Chemistry
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How to Name a Compound
If there is more than
one type of
substituent in the
molecule, list them
alphabetically.
Organic and
Biological
Chemistry
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Cycloalkanes
•  Carbon can also form ringed structures.
•  Five- and six-membered rings are most stable.
–  They can take on conformations in which their bond
angles are very close to the tetrahedral angle.
–  Smaller rings are quite strained.
Organic and
Biological
Chemistry
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Reactions of Alkanes
•  Alkanes are rather unreactive due to
the presence of only C—C and C—H
σ-bonds.
•  Therefore, they make great nonpolar
solvents.
Organic and
Biological
Chemistry
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Alkenes
•  Alkenes contain at least one carbon–carbon
double bond.
•  They are unsaturated.
–  That is, they have fewer than the maximum number of
hydrogens.
Organic and
Biological
Chemistry
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Structure of Alkenes
•  Unlike alkanes, alkenes cannot rotate freely
about the double bond.
–  The side-to-side overlap in the π-bond makes this
impossible without breaking the π-bond.
Organic and
Biological
Chemistry
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Structure of Alkenes
This creates
geometric isomers,
which differ from
each other in the
spatial arrangement
of groups about the
double bond.
Organic and
Biological
Chemistry
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Properties of Alkenes
Structure also affects the physical properties
of alkenes.
Organic and
Biological
Chemistry
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Nomenclature of Alkenes
•  The chain is numbered so the double bond gets the
smallest possible number.
•  cis-Alkenes have the carbons in the chain on the
same side of the molecule.
•  trans-Alkenes have the carbons in the chain on
opposite sides of the molecule.
Organic and
Biological
Chemistry
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Reactions of Alkenes
•  One reaction of alkenes is the addition
reaction.
–  In it, two atoms (e.g., bromine) add across the
double bond.
–  One π-bond and one σ-bond are replaced by two
σ-bonds; therefore, ΔH is negative.
Organic and
Biological
Chemistry
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Mechanism of Addition Reactions
•  It is a two-step mechanism:
–  The first step is the slow, rate-determining
step.
–  The second step is fast.
Organic and
Biological
Chemistry
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Mechanism of Addition Reactions
In the first step, the
π-bond breaks and
the new C—H
bond and a cation
form.
Organic and
Biological
Chemistry
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Mechanism of Addition Reactions
In the second step,
a new bond forms
between the
negative bromide
ion and the positive
carbon.
Organic and
Biological
Chemistry
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Alkynes
•  Alkynes contain at least one carbon–carbon triple
bond.
•  The carbons in the triple bond are sp-hybridized
and have a linear geometry.
•  They are also unsaturated.
Organic and
Biological
Chemistry
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Nomenclature of Alkynes
4-methyl-2-pentyne
•  The method for naming alkynes is analogous
to the naming of alkenes.
•  However, the suffix is -yne rather than -ene.
Organic and
Biological
Chemistry
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Reactions of Alkynes
•  Alkynes undergo many of the same reactions
alkenes do.
•  As with alkenes, the impetus for reaction is
the replacement of π-bonds with σ-bonds.
Organic and
Biological
Chemistry
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Aromatic Hydrocarbons
•  Aromatic hydrocarbons are cyclic hydrocarbons that
have some particular features.
•  There is a p-orbital on each atom.
–  The molecule is planar.
•  There is an odd number of electron pairs in the πsystem.
Organic and
Biological
Chemistry
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Aromatic Nomenclature
Many aromatic
hydrocarbons are
known by their
common names.
Organic and
Biological
Chemistry
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Reactions of Aromatic Compounds
•  In aromatic
compounds, unlike
in alkenes and
alkynes, each pair of
π-electrons does not
sit between two
atoms.
•  Rather, the
electrons are
delocalized; this
stabilizes aromatic
Organic and
compounds.
Biological
Chemistry
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Reactions of Aromatic Compounds
•  Due to this stabilization, aromatic compounds
do not undergo addition reactions; they
undergo substitution.
•  In substitution reactions, hydrogen is replaced
by a substituent.
Organic and
Biological
Chemistry
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Structure of Aromatic Compounds
•  Two substituents on a benzene ring could
have three possible relationships:
–  ortho-: On adjacent carbons.
–  meta-: With one carbon between them.
–  para-: On opposite sides of ring.
Organic and
Biological
Chemistry
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Reactions of Aromatic Compounds
Halogenation
Friedel-Crafts Reaction
Reactions of aromatic compounds often
require a catalyst.
Organic and
Biological
Chemistry
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Functional Groups
The term functional
group is used to
refer to parts of
organic molecules
where reactions
tend to occur.
Organic and
Biological
Chemistry
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Alcohols
•  Alcohols contain one or more hydroxyl groups,
—OH.
•  They are named
from the parent
hydrocarbon; the
suffix is changed to
-ol and a number
designates the
carbon to which the
hydroxyl is
attached.
Organic and
Biological
Chemistry
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Alcohols
•  Alcohols are much
more acidic than
hydrocarbons.
–  pKa ~15 for most
alcohols.
–  Aromatic alcohols
have pKa ~10.
Organic and
Biological
Chemistry
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Ethers
•  Ethers tend to be quite unreactive.
•  Therefore, they are good polar solvents.
Organic and
Biological
Chemistry
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Carbonyl Compounds
•  The carbonyl group
is a carbon-oxygen
double bond.
•  Carbonyl
compounds include
many classes of
compounds.
Organic and
Biological
Chemistry
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Aldehydes
In an aldehyde, at
least one hydrogen
is attached to the
carbonyl carbon.
Organic and
Biological
Chemistry
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Ketones
In ketones, there
are two carbons
bonded to the
carbonyl carbon.
Organic and
Biological
Chemistry
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Carboxylic Acids
•  Acids have a
hydroxyl group
bonded to the
carbonyl group.
•  They are tart tasting.
•  Carboxylic acids are
weak acids.
Organic and
Biological
Chemistry
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Esters
•  Esters are the
products of
reactions
between
carboxylic acids
and alcohols.
•  They are found in
many fruits and
perfumes.
Organic and
Biological
Chemistry
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Amides
Amides are formed
by the reaction of
carboxylic acids with
amines.
Organic and
Biological
Chemistry
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Amines
•  Amines are organic bases.
•  They generally have strong, unpleasant
odors.
Organic and
Biological
Chemistry
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Chirality
•  Carbons with four different groups attached to
them are handed, or chiral.
•  These are optical isomers or stereoisomers.
•  If one stereoisomer is “right-handed,” its
enantiomer is “left-handed.”
Organic and
Biological
Chemistry
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Chirality
S-ibuprofen
•  Many pharmaceuticals are chiral.
•  Often only one enantiomer is clinically
active.
Organic and
Biological
Chemistry
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Amino Acids and Proteins
•  Proteins are polymers
of α-amino acids.
•  A condensation
reaction between the
amine end of one
amino acid and the
acid end of another
produces a peptide
bond.
Organic and
Biological
Chemistry
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Amino Acids and Proteins
•  Hydrogen bonding in
peptide chains causes
coils and helices in the
chain.
•  Kinking and folding of
the coiled chain gives
proteins a
characteristic shape.
Organic and
Biological
Chemistry
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Amino Acids and Proteins
•  Most enzymes are
proteins.
•  The shape of the
active site
complements the
shape of the substrate
on which the enzyme
acts; hence, the “lockand-key” model. Organic and
Biological
Chemistry
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Carbohydrates
Simple sugars are
polyhydroxy
aldehydes or ketones.
Organic and
Biological
Chemistry
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Carbohydrates
•  In solution, they form
cyclic structures.
•  These can form chains
of sugars that form
structural molecules
such as starch and
cellulose.
Organic and
Biological
Chemistry
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Nucleic Acids
Two of the building blocks of
RNA and DNA are sugars
(ribose or deoxyribose) and
cyclic bases (adenine,
guanine, cytosine, and
thymine or uracil).
Organic and
Biological
Chemistry
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Nucleic Acids
These combine with
a phosphate to form
a nucleotide.
Organic and
Biological
Chemistry
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Nucleic Acids
Nucleotides combine
to form the familiar
double-helix form of
the nucleic acids.
Organic and
Biological
Chemistry
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