Chirality

Amino acids which are the building blocks of...

...enzymes and proteins are chiral, making all enzymes and proteins chiral

Isomers

Molecules that have the same chemical formula but different structural formulae

Stereoisomers

Molecules that have the same structural formulas and bonding patterns but different 3D arrangements of atoms in space

Types of stereoisomers

1. Geometric (cis vs. trans configs) 2. Optical aka enantiomer

Chiral

Molecules which cannot be superimposed upon their mirror image (asymmetrical)

Achiral

Molecules which can be superimposed upon their mirror image (symmetrical)

Enantiomers

A pair of molecules that're related as non-superimposable mirror images (e.g. R and L hand analogy)

Enantiomers have...

...opposite configurations

Chiral molecules are...

... 1. Chemically identical with identical physical properties, but they have unique 3D shapes. 2. Optically active

What defines chirality?

A tetrahedral carbon (aka stereogenic centre) bound to 4 *different* groups, giving rise to 2 stereoisomers

How can you tell enantiomers apart?

Each member of a pair of enantiomers rotates the plane of polarised light in an opposite direction, but by the same number of degrees (α)

Optically active

Can rotate the plane of polarised light

If one enantiomer rotates light by x degrees clockwise then...

...the other enantiomer rotates light x degrees anticlockwise

Dextrotatory

(+) positive, (d), (clockwise)

Levorotatory

(-) negative, (l), (anticlockwise)

Racemic mixture

50:50 mixture of 2 enantiomers

Racemic mixtures (d,l)/(+,-) are...

...optically inactive

Specific rotation formula

[α] = α/c*l

Specific rotation formula key

α: observed rotation in degrees
c: concentration in g/mL (use know and want to convert!)
l: length of path in dm

cm -> dm

divide by 10 as 10cm = 1dm

What is [α]D?

The wavelength of the typical 589nm light used from street lamps

Testing for chirality steps

1. Get mirror image of given molecule
2. Rotate 180 degrees
3. Check if identical to original, if yes then achiral, if no then chiral