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Biomolecular science
Isomerism and buffers-summer exam preparation stage 1 nutrition and dietetics Robert Gordon University
23
Science
Undergraduate 1
04/28/2008

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Term
Optical isomerism
Definition
Each of two or more forms of a compound that have the same structure but are mirror images of each other and typically differ in optical activity.

Optical isomer = enantiomer
Term
Enantiomer
Definition
Each of a pair of molecules that are mirror images of each other.

Enantiomer = optical isomer
Term
cis
Definition
[image]
Term
Structural isomers
Definition
have different structural formulas and different properties
ms: skeletal, positional, functional, group isomers.
Term
trans
Definition
Denoting or relating to a molecular structure in which two particular atoms or groups lie on opposite sides of a given plane in the molecule, in particular denoting an isomer in which substituents at opposite ends of a carbon=carbon double bond are also on opposite sides of the bond.
Term
Stereoisomers
Definition
Atoms are attached in the same order but are oriented differently in space.
Term
Geometric isomers
Definition
cis-trans isomers
Term
Why do geometric isomers exist?
Definition
Geometrics isomers exit because rotation about the double bond is very difficult.
Term
The golden rule of geometric isomers:
Definition
If one of the unsaturated carbon atoms is attached to two identical groups, cis-trans isomerism is not possible.
Term
Cis cyclic structure
Definition
groups orientated in the same way in relation to the plane of the ring.
OH _ OH
|/ \|
\_/
Term
trans cyclic structure
Definition
groups orientated in opposite ways to the plane of the ring.

OH _
|/ \
\_/|
OH
Term
Properties of geometric isomers:
Definition
Geometric isomers exhibit different physical and chemical properties.
Term
Chirality
Definition
Objects that cannot be superimposed upon their mirror image are said to be chiral objects.
Term
Achiral
Definition
Objects that can be superimposed on their mirror objects.
Term
Superimpose
Definition
[image]
Term
enantiomers
Definition
enantiomers are pairs of molecules that are non-superimposable mirror images of one another.
Term
Properties of enantiomers:
Definition
A pair of enantiomers tend to have the same chemical and physical properties but differ in their interaction with other chiral substances so have different biological properties.

Enantiomers also differ in their interaction with plane-polarized light.
Term
Polarimeter
Definition
Used to measure the direction and the degree of plane polarized light.

light enters, goes through a polaroid filter, the plane of the polarized light is then rotated and finally the analysing filter is rotated to measure the angle of rotation.
Term
Dextrorotary:
Definition
clockwise/positive rotation of polarized light.
Term
Levorotary:
Definition
anticlockwise/negative rotation of polarized light.
Term
Explain the interaction of chiral molecules and enzymes and give an example.
Definition
Enzymes are chiral and can only interact with molecules that have a complementary shape.
This gives selsctivity.

Drug interaction: Thalidomide- two enantiomers, one acts as an effective sedative, the other is teratogenic and causes birth defects.
Term
what happens to buffer solutions upon addition of a small amount of acid or base?
Definition
Upon addition of a small amount of acids or bases to a buffer solution it can resist change in hydronium ion and hydroxide ion concentration and consequently pH.
Term
Function of buffer solutions:
Definition
Buffer solutions are necessary to keep the correct pH for enzymes in many organisms to work.
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