Transcript functional groups

Carbon is Simply
Amazing.
Ch 4
2. Carbon atoms are the most versatile
building blocks of molecules
• With a total of 6 electrons, a carbon atom
has 2 in the first shell and 4 in the second
shell.
– Carbon has little tendency to form ionic
bonds by loosing or gaining 4 electrons.
– Instead, carbon usually completes its
valence shell by sharing electrons with
other atoms in four covalent bonds.
– This tetravalence by carbon makes large,
complex molecules possible.
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Fig. 4.4
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
FUNCTIONAL
GROUPS!
Why do we care about
functional groups anyway?
(Besides the fact that they’re
on the AP Test?)
See next slide for an
example of its importance!
1. Functional groups contribute to the
molecular diversity of life
• The components of organic molecules that are most
commonly involved in chemical reactions are known
as functional groups.
• Functional groups are attachments that replace one or more
hydrogen atoms to the carbon skeleton of the hydrocarbon.
• Each functional groups behaves consistently from
one organic molecule to another.
• The number and arrangement of functional groups
help give each molecule its unique properties.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• There are six functional groups that
are most important to the chemistry of
life: hydroxyl, carbonyl, carboxyl,
amino, sulfhydryl, and phosphate
groups.
• All are hydrophilic and increase
solubility of organic compounds in
water.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• In a hydroxyl group (-OH), a hydrogen atom forms a
polar covalent bond with an oxygen which forms a
polar covalent bond to the carbon skeleton.
• Because of these polar covalent bonds hydroxyl
groups improve the solubility of organic molecules.
• Organic compounds with hydroxyl groups are
alcohols and their names typically end in -ol.
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• A carbonyl group (=CO) consists of an oxygen
atom joined to the carbon skeleton by a double
bond.
• If the carbonyl group is on the end of the skeleton, the
compound is an aldelhyde.
• If not, then the compound is a ketone.
• Isomers with aldehydes versus ketones have different
properties.
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• A carboxyl group (-COOH) consists of a carbon
atom with a double bond with an oxygen atom and a
single bond to a hydroxyl group.
• Compounds with carboxyl groups are carboxylic acids.
• A carboxyl group acts as an acid because the combined
electronegativities of the two adjacent oxygen atoms
increase the dissociation of hydrogen as an ion (H+).
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• An amino group (-NH2) consists of a nitrogen atom
attached to two hydrogen atoms and the carbon
skeleton.
• Organic compounds with amino groups are amines.
• The amino group acts as a base because ammonia can
pick up a hydrogen ion (H+) from the solution.
• Amino acids, the building blocks of proteins, have amino
and carboxyl groups.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• A sulfhydryl group (-SH) consists of a sulfur
atom bonded to a hydrogen atom and to the
backbone.
• This group resembles a hydroxyl group in shape.
• Organic molecules with sulfhydryl groups are thiols.
• Sulfhydryl groups help stabilize the structure of
proteins.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• A phosphate group (-OPO32-) consists of
phosphorus bound to four oxygen atoms (three with
single bonds and one with a double bond).
• A phosphate group connects to the carbon backbone via
one of its oxygen atoms.
• Phosphate groups are anions with two negative charges
as two protons have dissociated from the oxygen atoms.
• One function of phosphate groups is to transfer energy
between organic molecules.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
2. The chemical elements of life: a review
• Living matter consists mainly of carbon, oxygen,
hydrogen, and nitrogen, with smaller amounts of
sulfur and phosphorus.
• These elements are linked by strong covalent bonds.
• Carbon with its four covalent bonds is the basic
building block in molecular architecture.
• The great diversity of organic molecules with their
special properties emerge from the unique
arrangement of the carbon skeleton and the functional
groups attached to the skeleton.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Testing…HYDROXYL
►What
is the functional group?
►It is POLAR (that bond between
oxygen and hydrogen look familiar?)
and it makes a molecule that is
attached to it WATER SOLUBLE.
►Anything with a hydroxyl is called an
alcohol.
Testing…Carbonyl?
What
is the functional
group?
It is POLAR. So anything
with this functional group is
WATER SOLUBLE.
It is found in sugars.
Aldehyde…ketone?
Testing…CARBOXYL
 Also polar. But that covalent bond
between oxygen and hydrogen is so
very polar that the hydrogen
reversibly dissociates as H+
 Since it donates protons, this group
might have what kind of properties?
 Compounds with this group are
called carboxylic acids.
Testing…AMINO
Again, it’s POLAR and soluble in water/
 Because it’s unshared pair of electrons
on the nitrogen can accept a proton (a
H+), amino acts a a weak base.
 Any compound with an amino
functional group is called an amine.

Testing…Sulfhydryl
• This has an atom of sulfur +
an atom of hydrogen (-SH)
• Helps stabilize the
structure of proteins
• Organic compounds with
this functional group are
called thiols
Testing…Phosphate
• This functional group has a
disassociated form of
phosphoric acid
• Phosphate has acidic properties.
Add On…Methyl
• Methyl (-CH3) can be considered a
functional group.
• Unlike all the others we talked about, it
is NONPOLAR and therefore
HYDROPHOBIC
• These properties will make it useful
when we talk about tertiary structure in
proteins
For the Quiz…
• You should have the structures
memorized in picture form
(That includes the difference between
single and double bonds, and where
these are placed.)
• You should know where these
functional groups are found.
• You should know what they are called.
Variations in Carbon Skeletons
• Hydrocarbons=molecules that include
only carbon and hydrogen
-these are major components of fossil
fuels
-framework for the diverse molecules
found in living organisms
-these are hydrophobic (WHY?)
Think: C-H bonds and C-C bonds…
The Three Types of Isomers
• Definition of Isomer= compound with
the same molecular formula but with
different structures and hence,
different properties
Structural Isomer
• Isomers that differ in the covalent
arrangement of atoms
• May also differ in location of double
bonds
Geometric Isomer
• Isomers share the same covalent
partnerships, but differ in spatial
arrangements
• Due to fact that double bonds DO NOT
allow atoms they join to ROTATE
FREELY
Enantiomer
• Mirror images of each other
• Two different spatial arrangements
around asymmetric carbon
• Usually one is biologically active and
other is not
• Even the subtle structural differences in two
enantiomers have important functional
significance because of emergent
properties from the specific arrangements
of atoms.
– One enantiomer of the drug thalidomide
reduced morning sickness, its desired effect,
but the other
isomer caused severe
birth defects.
– The L-Dopa isomer
is an effective treatment
of Parkinson’s disease,
but the D-Dopa isomer
is inactive.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 4.7