3.3 stereo chemistry

Question 1

what are isomers

Answer 1

molecules that have the same molecular formula but different structural formulae

Question 2

when do structural isomers occur

Answer 2

when atoms are bonded together in a different order in each isomer

Question 3

when do stereoisomers occur

Answer 3

the order of the bonding in atoms is the same but the spatial arrangement of the atoms is different in each isomer

Question 4

what are the two types of stereoisomers

Answer 4

geometric and optical

Question 5

what are geometric isomers

Answer 5

these occur when there is restricted rotation around a carbon-carbon double bond or a carbon-carbon single bond in a cyclic compound. they must have two different groups attached to each of the carbon atoms that make up the bond with restricted rotation.

Question 6

how can geometric isomers be labelled

Answer 6

cis or trans.

Question 7

what does the cis label mean

Answer 7

the substituent groups eg methyl are on the same side of the bond with restricted rotation

Question 8

what does the trans label mean

Answer 8

the substituent groups eg methyl are on different sides of the bond with restricted rotation

Question 9

what differences can be found in geometric isomers

Answer 9

differences in physical and chemical properties

Question 10

what are optical isomers

Answer 10

these occur in compounds in which four different groups are arranged tetrahedrally around a central carbon atom. they are asymmetric and are non super imposable mirror images of each other.

Question 11

what is meant by a chiral carbon

Answer 11

this a carbon atom that has four different groups are arranged tetrahedrally around it q

Question 12

how else can optical isomers be described

Answer 12

enantiomers

Question 13

what are the similarities between optical isomers

Answer 13

they have identical physical properties except for their effect on plane polarised light
they have identical chemical properties except when in a chiral environment such as that found in biological systems

Question 14

why are optical isomers optically inactive when they are mixed in equal amounts

Answer 14

because the rotational effect of the plane polarised light cancels out

Question 15

what is a racemic mixture

Answer 15

this is when the rotational effect of the plane polarised light cancels out, meaning the optical isomers are optically inactive