org3stereochemistry

It is February,1929. In a lonely cottage in Devonshire, G. Harrison, a middle-aged amateur mycologist (业余真菌学家,真菌学爱好者), has died shortly after eating a mushroom stew (炖菜) he prepared from warty caps (一种食用菇) collected in nearby Five-Acre Wood. Cause of death : poisoning by muscarine (蕈音xùn 毒碱), an alkaloid (生物碱) found in the fly agaric (蝇伞菌,一种毒菇).
CH 2N(CH 3)3+X -H
CH 3
H
H H OH
H O Did a deadly fly agaric find its way accidentally
into the mess of closely similar, but harmless
warty caps ?
Was a lethal dose of synthetic muscarine (filch-
ed from a London laboratory), deliberately and
with malice aforethought (预谋), added to the
stew pot ——perhaps by the lover of beautiful
Mrs. Harrison ?
Chapter 4 Stereochemistry
Isomerism (同分异构)
constitutional ~
(构造异构)
stereoisomerism
(立体异构)
configurational ~
(构型异构)
conformational ~
(构象异构)
cis-and trans-~
(顺反异构)
enantiomerism
(对映异构)
CH3CHCOOH
OH
lactic acid (乳酸) 3 forms
1. Optical activity (旋光性，光学活性)
A polarimeter (旋光仪) water ethanol lactic acid
Optically inactive The sample is "optically active " if it rotates the plane of polarized light.
(+)-lactic acid (-)-lactic acid
(±)-lactic acid racemic lactic acid
右旋乳酸
左旋乳酸外消旋乳酸A pair of enantiomers (一对对映体)Optically active
2. Specific rotation (比旋光度)[] = x D T αα
l c α:observed rotation l :sample path length (dm)
c :sample concentration (g/mL)
= +53.2°
（水）[]25D α
To be optically active , the sample must contain a chiral
substance and one enantiomer must be present in excess of the other.
All achiral substances are optically inactive .
Historical Origin of Stereochemistry
Louis Pasteur in 1848 noticed the sodium ammonium salt of optically inactive tartaric acid was a mixture of two mirror-image crystal forms.
Louis Pasteur’s discovery of enantioisomerism led, in 1874, to the proposal of the tetrahedral structure of carbon by van’t Hoff(a college student of the time, the first recipient of the Nobel Prize in Chemistry in 1901) and Le Bel.
Hermann Kolbe, one of the most eminent organic chemists of the time, criticized van’t Hoff’s publication on “The Arrangements of Atoms in Space” as a childish fantasy.
“He finds it more convenient to mount his Pegasus(飞马)(evidently taken from the stables of the Veterinary College) and to announce how, on his bold flight to Mount Parnassus(希腊中部的山;诗坛),he saw the atoms arranged in space.”
Optical activity
3.Chirality of molecules (分子的手性)
3.1 Chirality (手性) = “-handedness”
The mirror image(镜像)of
a left hand is a right hand.
Left and right hands are
not superposable(重合的).
achral (非手性)?
In 1894, William Thomson(Lord Kelvin) coined a word for this property. He defined an object as chiral if it is not superposable on its mirror image.
CHFClBr
CH 3CH(OH)COOH COOH H 3C OH H
CH 3
COOH
H HO A pair of enantiaomers:
One is (+)-and the other
is (-)-.
Chiral ?pen, shoe, glove, sock, scarf tied around your neck, pyramid, helix, double helix, your hand, your foot, your ear, your eye, your nose, yourself. pair of scissors
nail
screw
knife
Me Me
H
H 3.2 Symmetric factors(对称因素)3.2.1 Symmetric plane(对称面)
H
C
H Br
Cl C
对称面
CH 3
H 3C
H
H
H H
CH 3
CH 3CH 3
H
H
CH 3
H H H
CH 3H
H CH 3
H
H
H
H H
H
H H 3C CH 3
C
C
COOH
H
H
OH
HO HOOC
3.2.2 Symmetric center(对称中心)
CH 3
H Cl
CH 3
H
Cl
CH 3
H
H H
CH 3
H H 3C
H
H CH 3
H H
Any molecule with a plane of symmetry or a center of symmetry is achiral.
A molecule lacking a center of symmetry or a plane of symmetry is likely to be chiral .
We eat optically active bread and optically active meat, live in houses, wear clothes, and read books made of optically active cellulose.
Chirality is a phenomenon that pervades the university.
1)The human body is structurally chiral.
2)Helical seashells are chiral, and most spiral like a right-handed screw.
3)Many plants show chirality in the way they wind around supporting structures.
i)The honeysuckle (忍冬，金银花) winds as a left-handed helix. ii)The bindweed (旋花类植物) winds as a right-handed way.。