C9 Stereochemistry 3

Question 1

how does the amount of alternative configurations relate to the amount of stereogenic centres?

Answer 1

2^n
n being the amount of stereogenic centres in the molecule

Question 2

when there are 2 stereogenic centres, what is considered an enantiomer?

Answer 2

• molecules with opposite configurations at all centres
• eg. 1R, 2S and 1S, 2R
• eg. 1R, 2R, 3S and 1S, 2S, 3R (configurations have swapped at all 3 centres)

(the number relates to the stereogenic centre and the letter with it relates to the configuration at that centre)

Question 3

what is a diastereoisomer / diastereomer?

Answer 3

• stereoisomers which are not enantiomers
• eg. 1R, 2R and 1R, 2S because not all configurations have swapped

Question 4

what are 1-epimers and 2-epimers?

Answer 4

• the diastereoisomers that have changed at the 1 and 2 positions respectively
• eg. the 2 epimer of 1R, 2S, 3R is 1R, 2R, 3R (only 2 has changed)

Question 5

what are the properties of stereoisomers?

Answer 5

• enantiomers are chemically identical except in optical properties
• biological properties may differ
• diastereoisomers have different physical and chemical properties

Question 6

what is important to remember when considering conformation and configuration?

Answer 6

• a change in conformation does not affect configuration