s&r topic 4

Question 1

define enantiomers

Answer 1

molecules that are mirror images of each other
cannot be superimposed not each other
they are chiral

Question 2

how do you draw enantiomers

Answer 2

change wedged bonds to hashed and hashed bonds to wedged

or draw in a mirror line

Question 3

what are 5 similarities of enantiomers of the same molecule

Answer 3

all physical properties are the same

• mp
• bp
• density
• IR and NMR spectra are identical
• equal magnitude of optical rotation (but diff direction)

Question 4

name 2 differences of enantiomers of the same molecule

Answer 4

• smell

- direction of optical rotation

Question 5

what does optical rotation of an enantiomer measure

Answer 5

the angle of which an enantiomer rotates a plane of polarised light so it can pass through a liquid

Question 6

enantiomers that rotate light clockwise are called

enantiomers that rotate light anti-clockwise are called

Answer 6

dextrorotary

leavorotary

Question 7

what is the cahn-ingold-prelog system

Answer 7

used to assign a numerical priority to each substituent around a chiral centre

Question 8

name 3 rules of the cahn-ingold-prelog system

Answer 8

1. substituent directly bonded to centre with the highest atomic number takes priority
2. if there are two isotopes of the same element bonded to the centre, the heavier isotope takes priority
3. if atoms directly bonded to centre are the same, consider the next atom along

Question 9

how is the direction of the priority groups and therefore the label of chiral compounds found

Answer 9

the 4th priority group (lowest) is drawn going towards the back of the molecule/into the page and the direction is taken as 1 > 2 > 3

clockwise direction = (R) configuration (rectus)
anti-clockwise = (S) configuration (sinister)

if 4th priority group is not drawn at the back, the orientation must still be considered as if it were