CHAPT 3 : stereochemistry Flashcards Preview

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Flashcards in CHAPT 3 : stereochemistry Deck (10)
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1

Describe the classification of stereoisomers.

the atoms in stereochem are connected in the same way but their arrangement in 3d space is different
- conformational isomers interconvert rapidly and cannot be separated
( newman projection and cyclohexane)
- configurational isomers does not interconvert thus it can be separated
- geometrical isomers( cis trans isomers)
- optical isomers ( R/S enantiomers)

2

which is the most stable in newman projection

the staggered conformation is more stable compared to the eclipsed because in eclipsed conformation there is steric repulsion of the atoms in the front with those at the back

3

in cyclohexanes, which has the most stable conformation

chair conformation is more stable than boat conformation as there is steric repulsions in boat cyclohexane

4

what happens in a ring flip

atoms in axial position becomes equatorial position
vise vera
( will be a mirror image of each other)

5

what is the most stable cyclohexane conformation

It is the one with all the bulky substituents located at equatorial position ( diequatiorial form) in order to avoid
1,3-diaxial repulsion

6

what is geometric isomers

cis-trans isomers involving disubstituted alkenes
cis-isomers: 2 similar or identical groups are on the same side
trans-isomers: 2 similar or identical are groups are opposite sides

7

what is a stereogenic centre (stereo centre)

A carbon bonded to 4 different substituents

8

Difference between chiral molecules and achiral molecules

chiral molecules
- have a mirror image ( enantiomers )
- have a streo centre
- asymmetrical

Achiral molecules:
- no mirror image
- symmetrical

*carbons with double bonds are never chiral*

9

what are the 3 ways of drawing enantiomers

1. perspective formula
2. wedge and dash
3. Fischer projection formula

10

Determine the absolute configuration of a 3-dimensional chiral molecule using the R/S notation system.

1. rank the atoms based on atomic number
2. make the lowest priority away from you
3. if clockwise= R-configuration
if anti-clockwise= S-configuration

* if lowest priority is coming towards you, can change the config* R become S, vice vera