3) Fischer projections + optical activity

pages 5

What is a Fischer projection?

a two-dimensional representation of a three-dimensional organic molecule by projection

What is plane-polarized light?

light that oscillates (swings back and forth) in only one direction or plane; Normally, light waves vibrate in multiple directions, but when it passes through a polarizer, it filters out all but one specific orientation, creating plane-polarized light.

What does it mean when something is optically active?

When plane-polarized light interacts with a sample containing a single enantiomer, the light is rotated from its original orientation by some angle in either the clockwise or counterclockwise direction,

If the light is rotated counterclockwise then it’s said to be..

levorotatory (l or –).

If the light is rotated clockwise then it’s said to be..

dextrorotatory (d or +)

The angle of rotation is called the

specific rotation ([a]).

The specific rotation of enantiomers are

equal but opposite (if one is +13, the other is -13)

Do achiral molecules (such as Meso compounds) rotate plane polarized light?

Meso compounds CAN overlap on their mirror image, which cancels out their optical rotations. They are ACHIRAL

Polarimeter explaintation

Specific rotation equation

[ alpha ] = alpha / c x l

What does alpha stand for?

observed rotation

What does c stand for?

concentration of solution in g/ml

What does l mean?

length of the cell in decameters (1 dm = 10 cm)