topic 17

Question 1

what is a chiral centre

Answer 1

a carbon atom with four different groups bonded to it so the molecule has no line of symmetry`

Question 2

what is optical isomerism

Answer 2

a type of stereo isomerism chiral carbon atoms with non super imposable mirror images of each other

Question 3

how are chiral centres indicated

Answer 3

with an asterisk

Question 4

what are two different optical isomers called

Answer 4

enantiomers

Question 5

how do enantiomers differ from eachother?

Answer 5

they rotate the plane of polarised light

Question 6

what is a racemic mixture?

Answer 6

this is two enantiomers that exist in equal amounts( equimolar)

Question 7

how do enentiomers of the same molecule differ

Answer 7

they rotate light by the same degree in opposite directions

Question 8

what happens to light in the presence of a racemate

Answer 8

the plane of polarised light remains the same as the polarisation rotation is cancelled out

Question 9

what are the two ways that nucleophillic substitution can occur

Answer 9

the negative charge can leave the chiral carbon first so that the nucleophile can attack from any direction .

the nucleophile could attack at the same time as the negative charge leaves so that it can only attack from one direction.

Question 10

what is a carbonyl compound

Answer 10

a organic compouds containing a C=O group.and the functional group of -CO

Question 11

what are the most common carbonyl groups

Answer 11

aldehydes and ketones

Question 12

how are aldehydes produced

Answer 12

via the oxidation and distillation of primary alcohols

Question 13

what do aldehydes react with to form carboxyllic acids

Answer 13

potassium dichromate

Question 14

how are ketones formed

Answer 14

through the oxidisation and distillation of secondary alcohols

Question 15

whats the main difference between aldehydes and ketones?

Answer 15

the positioning of the CO group

Question 16

what is the positioning of the CO group on aldehydes

Answer 16

it is always on the end of an organic group and ends in -al

Question 17

how many of each atom is there in the atom proponal

Answer 17

3 carbons, 6 hydrogens. and one oxygen atom.

Question 18

what is tollens reagent used for

Answer 18

to distinguish between aldehydes and ketones

Question 19

why is tollens reagent heated in a water bath and not under a flame

Answer 19

this is a safety precaution because aldehydes and ketones are very flammable

Question 20

how do we test for aldehydes and ketones?

Answer 20

acidified potassium dichromate (K2Cr2O7)

Question 21

what does potasssium dichromate show for the presence of aldehydes and ketones

Answer 21

it oxidises aldehydes. aldehydes turn from orange to green

no observations for ketones

Question 22

what functinal group does carboxyll have

Answer 22

-COOH

Question 23

what bonds do carboxyllic acids have

Answer 23

C=O(carbonyl group) bond and a -OH bond (a

Question 24

whats the general formula for aldehydes?

Answer 24

RCHO

Question 25

how are carboxylic acids formed from aldehydes

Answer 25

they are oxidised in the presence of acidified potassium dichromate (VI)

Question 26

what is the general formula for ketones

Answer 26

RCOR | C=O

Question 27

where is the carbonyl group on ketones

Answer 27

in between two hydrocarbon groups

Question 28

what alcohols can be oxidised

Answer 28

primary and secondary

Question 29

what happens when primary alcohols are heated in the presence of acidified potassium dichromate

Answer 29

an aldehyde is formed

Question 30

what happens when secondary alcohols are oxidises in the presence of K2Cr2O7

Answer 30

ketones are formed

Question 31

what is potassium dichromate used as and why

Answer 31

an oxidising agent because it is reduced in the reaction

Question 32

what will be observed when a tertiary alcohol reacts with potassium dichromate

Answer 32

no colour change is observed

Question 33

how can oxidation reactions to form carbonyl compounds from alcohols be reversed

Answer 33

they can be reversed through reduction reactions using lithium tetrehydridoaluminate in a dry ether

Question 34

why is the reduction reaction carried out in a dry ether

Answer 34

because lithium aluminium hydride reacts violently with water

Question 35

what is an arene

Answer 35

an aromatic compound that contains a benzene ring

Question 36

do arene have low or high boiling points and why

Answer 36

low boiling points because they are non polar and cant be dissolved in water

Question 37

do arenes have low or high melting points and why

Answer 37

high because of the high stability of the delocalised benzene ring

Question 38

how are the pi bonds in benzene formed

Answer 38

there is a delocalised outer electron in the p-orbital in each carbon going into the centre to form an overlapping ring

Question 39

why doesnt benzene undergo electrophillic addition

Answer 39

this would mean that the stable ring of electrons would be broken so instead electrophillic substitution occurs.

Question 40

what is halogenation

Answer 40

an electrophillic substitution reaction where benzene reacts with a halogens in the presence of a catalyst

Question 41

what is an example of a catalyst for halogenation reactions

Answer 41

FeBr3 iron(III) bromide

Question 42

what functional group is linked with carboxyllic acids

Answer 42

-COOH

Question 43

what is the general formula for grignards reagent and what is each letter

Answer 43

RMgX R- alkyl group Mg-magnesium X-halogen

Question 44

what is an alkyl group example

Answer 44

methyl ethyl

Question 45

what is an amine

Answer 45

when an alkyl group replaces a hydrogen on ammonia

Question 46

what is the purpose of grignards reagent

Answer 46

to lengthen the carbon chain

Question 47

how do you distinguish between the classification of amine i.e primary secondary or tertiary

Answer 47

primary is only one alkyl group secondary is two alkyl groups tertiary is two alkyl groups that have displaced the hydrogen in ammonia

Question 48

what is formed when grignards reagent is reacted with carbon dioxide and hydrolysed

Answer 48

a carboxylic acid

Question 49

what is formed when grignards reagent is reacted with a carbonyl compound and hydrolysed?

Answer 49

an alcohol