Stereochemistry

Question 1

stereochemistry

Answer 1

study of 3D shapes of molecules

Question 2

isomers

Answer 2

molecules which posses the same molecular formula but different structural connectivity

Question 3

optical isomers/stereoisomers

Answer 3

differ in the way they rotate plane-polarised right

there are two types: enantiomers and diastereoisomers

Question 4

enantiomers

Answer 4

molecules that are mirror images of each other and not superimposable (chiral)
eg. left and right hands

Question 5

achiral

Answer 5

have a plane of symmetry

have two identical substituents for the mirror image to be superimposable

Question 6

for tetrahedral to be chiral

Answer 6

it must have 4 different substituents

a carbon with 4 different substituents - asymmetric carbon centre or sterogenic centre

Question 7

molecules with more than one stereoisomer

Answer 7

molecules with n stereocentres have a maximum of 2^n stereoisomers

Question 8

diastereoisomers

Answer 8

stereoisomers that are not mirror images of each other (not enatiomers) - RR or SS, not SR or RS

Question 9

meso compound

Answer 9

the same molecule orientated differently and are superimposable. They are chiral with two or more sterocentres and are optically inactive

Question 10

chiral molecule reactions

Answer 10

react differently even though they seem so similar

Question 11

assigning configuration to sterogenic centres

Answer 11

chiral centres can be R(right) or S (left)

1. locate the stereogenic centre and identify the four different substituents
2. assign priority (1-4)
3. rotate so that the lowest priority is away from you. draw a curve from the first priority, to the second and then the third. Determine the direction

Question 12

assigning priority

Answer 12

1. highest priority to the atom with the highest atomic number
2. if the two substituents are the same, proceed to the next difference
3. groups with pi bonds are given single bond equivalents by duplication or triplication of multiply bonded atoms (C=O is C binded to two Os)

Question 13

optical activity

Answer 13

• boiling point, melting point and solubility are the same for enantiomers
• interact differently with the plane-polarised light - optical rotation

Question 14

plane polarised light

Answer 14

waves are oscillating in a single plane perpendicular to the direction of propagation of light while in ordinary light, oscillation occurs in all planes.
when it passes through a chiral molecule, light interacts with the electron cloud and rotates

Question 15

racemic mixtures

Answer 15

equal amounts of two enantiomers in the solution and rotation is cancelled out. optically inactive

Question 16

rotated counterclockwise

Answer 16

-, L form

Question 17

rotated clockwise

Answer 17

+, D form