3.3.7 Optical Isomerism Knowledge

Question 1

define a chiral

Answer 1

a molecule which can exist as a pair of optical isomers

Question 2

define a chiral centre

Answer 2

the carbon which is attached to four different groups

Question 3

what is a stereogenic centre

Answer 3

a chiral centre

Question 4

what is an asymmetric carbon

Answer 4

a chiral centre

Question 5

define an enantiomer

Answer 5

each optical isomer is an enantiomer

Question 6

define enantiomerically pure

Answer 6

a sample contains only one optical isomer

Question 7

define optically active

Answer 7

will rotate the plane of polarised light

Question 8

define a racemic mixture

Answer 8

a mixture which contains equal quantities of enantiomers

Question 9

define structural isomerism

Answer 9

same molecular formula, different structural formula

Question 10

define chain isomerism

Answer 10

• when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same
• This is caused by branching

Question 11

define positional isomerism

Answer 11

• arise from differences in the position of a functional group in each isomer
• The functional group can be located on different carbons

Question 12

define functional group isomerism

Answer 12

When different functional groups result in the same molecular formula

Question 13

describe the chemical properties of functional group isomers

Answer 13

The isomers have very different chemical properties as they have different functional groups

Question 14

define stereoisomerism

Answer 14

same structural formula, different arrangement of atoms in space

Question 15

how does geometrical isomerism arise

Answer 15

• Each C atom in the C=C bond has 2 different groups attached
• C=C restricts rotation

Question 16

define opitcal isomerism

Answer 16

non-superimposable mirror images

Question 17

how does optical isomerism arise

Answer 17

arises around a chiral carbon: a carbon atom bonded to 4 different groups

Question 18

how do optical isomers interact with polarised light

Answer 18

• Optical isomers rotate the plane of polarised light
• One isomer will rotate it clockwise, the other isomer will rotate it anti-clockwise

Question 19

what qualities do optical isomers share

Answer 19

• MP and BP
• solubility in a range of solvents
• Mr
• peaks in their NMR spectrum, IR spectrum, and Mass spectrum

Question 20

why is considering optical isomers important in the pharmaceutical industry

Answer 20

Many optical isomers have the same chemical reactivity, however if they are used as a drug, both isomers may not work in the same way when inside cells

Question 21

what are the 3 options When producing a new drug with optical isomers

Answer 21

• supply the drug as the racemic mixture
• make the drug as a racemic mixture and then separate out the 2 isomers.
• find a method of synthesis in which only one enantiomer is formed.

Question 22

what is the problem with supplying drugs as racemic mixtures

Answer 22

• runs the risk of unwanted side effects caused by the other isomer
• even if there are no side effects, 50% of the drug being administered is ineffective which is wasteful and inefficient

Question 23

why is it difficult to make drugs as a racemic mixture and then separate out the 2 isomers.

Answer 23

this is very challenging as 2 optical isomers are so similar that very few methods are available to separate them apart.

Question 24

evaluate the option of finding a method of synthesis in which only one enantiomer is formed in drug production

Answer 24

this can be very challenging but many starting materials which come from plants form in nature as single enantiomers, and so using one as the starting material can help ensure that one optical isomer forms