Lecture 1 Flashcards
Types of Isomers
-Same moleculare formular and different connectivity = isomers and constitutional
-Stereoisomers = same molecular formular and same connectivity
What is CHIRAL?
Molecules which cannot be superimposed upon their mirror images
What is ACHIRAL?
Molecules which can be superimposed upon their mirror images
What is Enantiomer? (Optical isomers)
A pair of molecules that are related as non-superimposable mirror images
What are CHIRAL molecules ? (Optical isomers)
-Chiral molecules are chemically identical to each other
-have unique 3D shapes, making them mirror-images that are not superimposable on each other.
- may possess very different biological properties.
This is very important in drug – enzyme / receptor interactions.
Stereoisomer shape
Tetrahedral carbon
-4 different groups need to attatched for chrial centre, tetraheadral
3d structure
When do molecules become Chiral?
Achrial and Chiral Molecules
Enantiomers-non-superimposable
Why is Chirality important in nature?
-Imagine that your hand is the latest blockbuster drug and works by the
inhibition of a specific enzyme the left baseball mit
-Racimic mixtures
-Right hand finds another target (enzyme) when it doenst fit
Could help or have adverse affects
-The drug is chiral so has two enantiomers and the enzyme is also chiral but is present in only one chiral form in nature
-Only 50% of the drug can interact with baseball mit (left hand) enzyme leaving the other half of the drug (right hand) inactive
-If the right hand can undergo an unwanted interaction with a different enzyme (e.g. a right handed glove) then a drug side effect can occur
Chiral Carbons
Tetrahedral carbon attached to 4 different atoms or groups of atom
Its mirror image will be a different compound (enantiomer)
Achiral and chiral molecules
Enantiomers – non-superimposable
Why is Chirality so Important in Nature?
-Imagine that your hand is the latest blockbuster drug and works by the
inhibition of a specific enzyme the left baseball mit
-Racimic mixtures
-Right hand finds another target (enzyme) when it doenst fit
Could help or have adverse affects
-The drug is chiral so has two enantiomers and the enzyme is also chiral but is
present in only one chiral form in nature
-Only 50% of the drug can interact with baseball mit (left hand) enzyme leaving the other half of the drug (right hand) inactive
-If the right hand can undergo an unwanted interaction with a different enzyme (e.g. a right handed glove) then a drug side effect can occur
Chiral Carbons
Is 2-Chloropropane Chiral?
Not chiral as you can superipose as plane of symmetry
Is 3-Methylpentane Chiral?
Not chrial as can be superimposed
Is 3-Methylhexane Chiral?
General rule
- Compounds with four different groups around a carbon atom generate a chiral molecule.
- The carbon atom with the four different groups is said to be a chiral center or a stereogenic centre.
Enatiomers
-Stereoisomers which are non-superimposable mirror images
have identical PHYSICAL properties
-have identical PHYSICAL properties e.g. melting point, boiling point, density etc
-Each member of a pair of enantiomers rotates the plane of polarised light in an opposite direction
-Chiral molecules are optically active
Difference between Two Enantiomers
Plane-polarized Light
-Verticle line can go through polarizer
-By the time it passes all the lines are aligned
-Chrial molecule can rotate the light
-Angle determined by analyzer, rotate anylizer until light is seen at the waves its at
How to tell difference between two enantiomers?
- If one enantiomer rotates plane polarized light by x° in
a clockwise direction, then the other enantiomer will rotate
plane polarized light by x° in the counterclockwise direction.
-d - dextrorotatory - (+) enantiomer = rotate clockwise
-l - levorotatory - (-) enantiomer = rotate counterclockwise
-A racemic mixture is a 50:50 mixture of two enantiomers
for example the (d,l) or (+,-)-3-methylhexane mixture will give no
optical rotation as they will cancel each other out
Example – Enantiomers of Lactic Acid Found in Sour Milk
Racemic Mixture Example – Lactic Acid
50:50 mixture of enantiomers is called a racemic mixture
Specific Rotation
-Observed rotation depends on the length of the cell and concentration, as well as the strength of optical activity, temperature, and wavelength of light.
Specific Rotation: Examples
Summary
-Achiral molecules: Can be superimposed on their mirror images. They are optically inactive.
-Chiral molecules: cannot be superimposed on their mirror images. They are optically active.Tetrahedral carbon with 4 different groups attached.
-Optically active molecules: can rotate the plane of polarised light.
-Enantiomers: are stereoisomers which are non-superimposable mirror images i.e. a chiral molecule and its mirror image.
-Racemic mixture: is a 50:50 mixture of enantiomers.
A racemic mixture is optically inactive.
