isomerism

Question 1

define structural isomers

Answer 1

compounds that have the same molecular formula but different structural formula.

Question 2

what are chain structural isomers

Answer 2

structural isomers which have different arrangements of the carbon skeleton

Question 3

properties of chain structural isomers

Answer 3

similar chemical properties
different physical properties
(more branching results in lower boiling point)

Question 4

what are positional structural isomers

Answer 4

structural isomers which have the same functional group but the functional group is in a different position on the carbon skeleton.

Question 5

properties of positional structural isomers

Answer 5

similar chemical properties
slightly different physical properties

Question 6

what is a functional group structural isomer

Answer 6

structural isomers which have different functional groups

Question 7

properties of functional group structural isomers

Answer 7

different chemical properties
different physical properties

Question 8

define stereoisomerism

Answer 8

is shown in molecules that have the same molecular formula and same bonds present, but different 3 dimensional orientation of their atoms in space

Question 9

Z

Answer 9

same side

Question 10

E

Answer 10

different side

Question 11

what two characteristics does a molecule need to show geometric isomerism

Answer 11

double bond
the two groups on the carbons of the double bond should be different

(both carbons can have the same two groups as long as the 2 differ from each other)

Question 12

what is geometric isomerism

Answer 12

occurs around double bonds. due to their restricted rotation around the double bond these molecules do not readily interconvert

Question 13

define optical isomers

Answer 13

are molecules which are isomers which are non superimposable mirror images of each other

Question 14

what is a chiral carbon

Answer 14

a carbon with 4 different groups attached to it

(often means a molecule shows optical isomerism)

Question 15

what key property do optical isomers show regarding plane polarised light

Answer 15

optical isomers rotate the plane of plane polarised light. each isomer will rotate the light by the same amount but in the opposite direction.

Question 16

what is a racemic mixture

Answer 16

a solution which contains equal numbers of moles of both optically active isomers/enantiomers of a compound

Question 17

why are racemic mixtures not optically active

Answer 17

optical rotations will cancel out

Question 18

which nuleophillic substitution mechanism do tertiary halogenoalkanes react via

Answer 18

SN1

Question 19

which nucleophillic substitution mechanism do primary halogenoalkanes react via

Answer 19

SN2

Question 20

what is steric hindrance

Answer 20

large groups getting in the way of attacking species

Question 21

do primary or tertiary halogenoalkanes have a lower steric hindrance (and therefore lower stability)

Answer 21

primary

Question 22

why does SN2 mechanism mean optical activity

Answer 22

SN2 can only be attacked from 1 angle (opposite side of leaving group)
all molecules form bonds in the same place
pure therefore shows optical activity

Question 23

why does SN1 mechanism mean no optical activity

Answer 23

can be attacked from various places
bonds can form in various places
forms a racemic mixture of the 2 isomers
optical activity of each isomer cancels out so none shown