Functional Groups
aldehyde
• Definition: an organic compound
containing a Carbonyl group ( C=O ).
The aldehyde group is generaly written -CHO
•the name Aldehyde comes from Alcohol-dehydrogenated meaning the loss
of hydrogen:
Benzaldehyde: aroma in cherries, almonds,
perfumes
Carboxyl Group
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Definition: a Carboxyl group ( -COOH), double bonded to an oxygen and
single-bonded to the oxygen of the hydroxyl group
Polar, water-soluble
The H+ dissociates and thus has acidic properties. Compounds with this
functional group are called carboxylic acids
The Carboxyl group is generally written -COOH
Carboxylic acids are the most important acids of organic chemistry. They are present
or in derived form in many natural substances:
Amino acids (building blocks of proteins). Note that the amino acids also contain an
amine group.
Below is given the structure of alanine
Fatty acids (building blocks of lipids) are long aliphatic chains terminated by the
carboxyl group.
The structure of stearine is given below.
Fatty acid
Glutamic acid
Carbonyl Group
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Definition: functional group consisting of a carbon atom double-bonded to
oxygen
(-CO)
Polar, involved in H-bonding and molecules with this functional group are
water-soluble
Found in sugars
If the carbonyl is at the end off the carbon skeleton-the compound is an
aldehyde
If the carbonyl is at the end of the carbon skeleton, the compound is a
ketone
Alcohol
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Definition: an alcohol is an organic compound containing a hydroxyl group (
O-H ).
The molecule on the left (methanol) shows the alcohol functional group
OH-CH2-CH2-OH ethylene glycol
(antifreeze)
Amine
Definition: an Amine is a derivative of ammonia ( NH3 ) in which
hydrogen atoms are replaced by R group
caffeine
Alanine & cysteine
Phosphate group
• Definition: functional group which is the
dissociated form of phosphoric acid
• Has acid properties since it loses H+ (protons)
• Polar and soluble in water
• Important in cellular energy storage and transfer
(ATP)
Sulfhydryl group
• Definition: functional group consisting of an atom of sulfur bonded to
an atom of hydrogen
• Help stabilize structure of proteins-disulfide bridges in the tertiary
structure of proteins
• Called thiols when found in organic compounds
Carbon atoms and molecules of carbon
hexane
Methane & ethane
Branchingisohexane
Single, double, triple bonds
Ringcyclohexane
Isomers have the same molecular formula but different
structures and different properties
• STRUCTURAL
BOTH HAVE THE SAME MOLECULAR
FORMULA C6H14
BUT DIFFERENT STRUCTURAL
FORMULAS
Structural isomers
• GEOMETRIC
These two chlorine atoms are locked on
opposite sides of the double bond. This is
known as the trans isomer the two
chlorine atoms are locked on the same
side of the double bond. This is know as
the cis isomer. (Hint: if you build models
and have to take it apart-geometric
isomer)
free rotation about single bonds;
these two structures represent
the same molecule (Hint: if you
build model-you just have to
rotate c-c bond- not an isomer)
Cis/trans geometric isomers
• In triglycerides fatty acids may contain double bonds, which can be
in either the cis or trans configuration .
• Fats with at least one double bond between carbon atoms are
unsaturated fats. When some of these bonds are in the cis
configuration, the molecules cannot pack tightly, so they remain
liquid (oil) at room temperature.
• triglycerides with trans double bonds (called trans fats), have are
linear fatty acids that are able to pack tightly together at room
temperature and form solid fats.
• ENANTIOMERS
• Whenever a carbon atom has four different
structures bonded to it, two different molecules
can be formed. (chiral means the central C is
bonded to 4 different groups or atoms)
• EXAMPLE: the amino acid alanine. Bonded to
its alpha carbon atom are:
• a carboxyl group (COO−)
• an amino group (NH3+)
• a methyl group (CH3)(its R group)
• a hydrogen atom
• If you orient the molecule so that you look
along it from the COO− group to the NH3+
group, the methyl (R) group can extend out
• to the left, forming L-alanine (shown below on
the left) or
• to the right, forming D-alanine (on the right).
• Although they share the same chemical formula, they
are not interchangeable any more than a left-hand glove
is interchangeable with right-hand glove.
• 19 of the 20 amino acids used to synthesize proteins can
exist as L- or D- enantiomorphs. The exception is
glycine, which has two (indistinguishable) hydrogen
atoms attached to its alpha carbon.
• L amino acids are used exclusively for protein synthesis
by all life on our planet. (Some D amino acids are used
for other purposes.)
• The function of a protein is determined by its shape.
• A protein with a D amino acid instead of L will have its R group
sticking out in the wrong direction.
• Many other kinds of organic molecules exist as enantiomers. Usually
only one form is active in biological systems. For example, if one
form binds to a receptor protein on the surface of a cell, the other
probably cannot.
• Cells usually synthesize only one form. However, chemical
synthesis in the laboratory or pharmaceutical factory usually
produces equal amounts of the two enantiomers — called a
racemic mixture.
• Example: The drug albuterol (e.g., Proventil®) contains equal
amounts of two enantiomers. Only one of them is effective, and the
other may be responsible for the occasional unpleasant side-effects
associated with the drug (which is used to dilate the bronchi, e.g,
during an attack of asthma).
Chiral compounds
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Some chemical compounds have optical activity in the sense that these compounds have the
ability to rotate the plane of polarized light. Polarized light has light waves all traveling parallel to
each other. Ordinary light has light waves traveling in all directions. When polarized light is passed
through a solution of an optically active compound, the plane of polarization is rotated to the right
or the left. The angle of rotation can be measured in a polarimeter.
An optically active organic compound can be identified by finding a chiral carbon. A chiral carbon
is one that has four different "groups" attached to it. The groups can be anything from a
single H to functional groups to one or more other carbons. See bromochloroiodomethane on the
left - it has 3 halogens and one hydrogen.
In relatively complicated compounds, each carbon must be examined carefully to determine
whether it is chiral. Some compounds may have two or more chiral carbon centers such as in
carbohydrates.
See glyceraldehyde : Carbon # 1 has only three groups attached. Carbon # 3 has two hydrogens
which count as 2 of the same groups. Finally, carbon # 2 has four different groups attached.