Stereochemistry Flashcards
Whats the sawhorse representation of a compound?
Like with newman projections, A sawhorse projection is a view of a molecule down a particular carbon-carbon bond, and groups connected to both the front and back carbons are drawn using sticks at 120˚ angles
Whats the configuration of a compound?
The molecular geometry of a molecule resulting from spatial arrangement of bonds
What does the following mean:
- constitution
- empirical formula
- molecular formula
-
structural formula
5.
What is meant by the word isomers?
What are the types of isomers?
these are substances which have the same composition and molecular weight, but they differ in properties
There are structural isomers and stereoisomers
What are enantiomers?
These are pairs of isomers which are mirror images and are non-superimposable
Whats meant by an Achiral molecules and whats meant by a Chiral molecule?
Achiral molecule: Mirror images that are superposable
Chiral molecule: Mirror images that are non-superimposable
All physical properties of enantiomers are identical, except one which is?
optical rotations
The extent to which enantiomers rotate polarised light is measure by what?
What does this factor depend on?
The extent to which enantiomers rotate polarised light is measured by an angle of rotation (alpha) in a so called polarimeter
The angle of rotation depends on the concentration of the solution (c), the path length of the cell (l) and the specific rotation, which is characteristic of the molecule
Whats a racemic mixture?
When the ratio’s non 1:1 what is the mixture said to be?
If theres only one enantiomer present, whats the mixture said to be?
Racemic mixture: a 1:1 ratio of enantiomers
Enantioenriched: When the ratio is not 1:1
Enantiopure or Homochiral: When there is only presence of one enantiomer
What are Diastereomers?
A pair of stereomers which do not bear mirror-image relation to each other
Whats means by a compound having a meso-form?
Structures which have stereogenic centres, but are also achiral
Whats a cis-isomer and a trans-isomer ?
Cis-isomer: identical substitutents are located on the same side of the double bond
Trans-isomer: identical substituents are located on the opposite side of the double bond
Whats Fischer representations?
LOOK UP
Alkenes can gave E/Z configuration. what does this mean?
E (entgegen= opposite/across): when the two highest priority groups are on the same side of the double bond
Z(Zusammen= together): If the two highest priority groups are on the opposite side of the double bond
Whats the R and S configuration of atoms? How are these assigned?
- give each atom connected to the chiral centre a priority based on its atomic number (the higher the atomic number, the higher the priority). Only look at what it is directly attached to, not further along the chain. E.g. of there is a hydroxyl group, this is a higher priority then a carboxyl group as the first thing its attached to is OH where as in the carboxyl group its only O
- draw an arrow starting from priority one to priority 4 for instance
- If the arrow goes clockwise the absolute configuration is R
- if the arrow goes counterclockwise the absolute configuration is s
Nb. The hydrogen has to be facing away from the place (dashed lines) if its towards the plane (wedge) then if you have an R configuration it would become S as the moleucle has to be rotated to get the H in the right orientation
Whats a staggered conformation?
When the substituents are locatted as far away as possible from one another
Whats an eclipsed conformation?
When the substituents are located, in pairs, in the same plane
Look up and practice newman projections
What conformation can cycle hexanes form?
Chair conformations
How many possible types of chair conformations are there for cycle alkanes and what are they in?
There are two possible chair conformations and thyey are in constant equilibrium
Drae HC(Cl).Br.I in the (R)-configuration
Look at chem work shop 2
How do you know if a molecule is a diastereomer or an enantiomer based on the R and S configuration of the molecule?
- identify the stereogenic centres
- assign prioirites for each centre and work out what absolute configuration each centre is
- When comparing pairs of molecules if your get a pair that is S,S and then S,R its an diastereomer
- if you get a pair that S,S and R,R then its an enantiomer
enantiomer: R and S and opposite
diaseteromer: R and S has a part inverted
