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Carboxylic acids. 1 C: formic acid, methanoic acid 2 C’s: acetic acid, ethanoic acid 3 C’s: propionic acid, propanoic acid 4 C’s: butyric acid, butanoic acid. Aspirin : Should you take a daily dose?. (Prostaglandins F 2 a ).
Prostaglandins are involved in the regulation of a variety of physiological
phenomena, including inflammation, blood clotting, and the induction of labor. Aspirin act by blocking the biosynthesis of prostaglandins in the cell.
making a carboxylic acid more acidic.
making a carboxylic acid less acidic.
Think like a wise man
but express yourself like
an ordinary one.
is the study of the three-dimensional structure of molecules.
Isomers : Different compounds that have the same
Stereoisomers : Isomers that have the same bonding sequence
but differ in the orientation of their atoms in space.
Late 50’s, thalidomide was prescribed as an analgesic for morning sickness and used extensively in Europe and Canada despite strong warning that it not be used by pregnant women.
Each enantiomer of a stereoisomeric pair is optically active and has an equal but opposite-in-sign specific rotation.
Although two enantiomers have identical boiling points and melting points, they rotate the plane of polarized light in opposite directions. A polarimeter is used to measure the optical rotations of enantiomers.
Specific rotation, [a] = amount (degrees) that a substance rotates plane polarized light expressed in a standard form.
Carvone from spearmint: [α]D = –62.5º
Lactic acid from muscle tissue: [α]D = +2.5º
Lactic acid from sour milk: [α]D = –2.5º
All objects may be classified with respect to chirality (from the Greek cheir = hand):
Chiral = Objects that are different from theirs mirror image;
i.e. golf clubs, scissors; enantiomers are chiral.
Achiral = Objects that are identical with theirs mirror image;
i.e. a pencil, a T-shirt.
Achiral molecule : water
Chiral molecules have chiral center (or stereo or stereogenic center):
an atom attached to 4 different atoms or groups.
The CIP system of nomenclature.
(R. S. Cahn, C. K. Ingold and V. Prelog)
application of two rules:
The Sequence Rule
The Viewing Rule
substituents, they are treated as an equivalent set of single-
bonded atoms. i.e. C2H5– < CH2=CH– < HC≡C–
Twist the lowest
priority to the
If you have troubles looking at the stereocenter, try Fischer Projections.
1) Rotation on page 180˚ is allowed for Fischer projection.
2) One group can be held steady while the other three rotate in either
a clockwise or a clockwise direction.
of lowest (4th) priority at the top or bottom of the Fischer
projection if it is necessary.
1 to 2 to 3, and assign R (clockwise) or
(+)-Pseudoephedrine and (-)-Pseudoephedrine are diastereomers of (+)-Ephedrine.
melting points, boiling points, solubities in solvent, etc.
Enantiomers: non-superimposable (different) mirror images; most of chemical and physical properties are identical.
Diastereomers: are stereoisomers that are not mirror images (all stereoisomers except enantiomers) and have different chemical and physical properties.
Cahn-Ingold-Prelog R/S notation = Specifies absolute configuration of a chiral center;
there is no correspondence between R and + or S and –
an achiral molecule with 2 or more chiral centers and
an internal plane of symmetry; the molecule is achiral.
Number of stereoisomers = a molecule with n stereogenic centers (and for which a meso isomer isn’t possible) will have 2n stereoisomers.
one specific enantiomer leaving the other alone.
diastereoisomers. Once separated the diasteriosomeric
forms are converted back to enantiomers in separate
E (German, entgegen for opposite) to designate the stereoisomers.
One learns one’s most valuable lessons through hardships.