unit 6 section 2 aromatic compounds and amines

Question 1

what do all aromatic compounds contain

Answer 1

they all contain a benzene ring

Question 2

what is the formula for benzene

Answer 2

C6H6

Question 3

what is the structure of a benzene ring

Answer 3

it has a planar cyclic structure - all the carbons are joined together in a flat ring

-each carbon atoms forms one covalent bond with the other carbons it is connected to and one to one hydrogen.

Question 4

where is the final unpaired electron on each carbon located in a benzene ring

Answer 4

they are located in the p-orbital and they stick out above and below the plane of the benzene ring.

the p-orbitals of each carbon combine to form a ring of delocalised electrons

Question 5

why are the electrons in the benzene ring said to be delocalised

Answer 5

this is because the electrons dont belong to a specific carbon atom

Question 6

why is benzene more stable than cyclohexane

Answer 6

this is due to the delocalised electrons in the benzene ring. in the delocalised electron ring, the electron density is shared between more atoms, this means the energy of the molecule is lowered and is therefore more stable.

Question 7

what is the prefix and suffix for naming aromatic compounds

Answer 7

prefix - phenyl or phen ( used if the benzene is not the main functional group )
suffix - benzene

Question 8

how do you name a aromatic compound if it has more than 1 functional group

Answer 8

if it is the same functional group, you count from any functional group and use the smallest number.
if it uses different functional group, you count from which ever functional group is used as the suffix in the name of the compound

Question 9

explain why aromatic compounds undergo electrophlic substitution reactions instead of electrophilic addition reactions

Answer 9

it is because the benzene ring is so stable, instead it undergoes electrophilic substitution where one hydrogen or functional group of the compound is replaced with the electrophile

Question 10

explain the nitration of benzene

Answer 10

this is done by warming benzene with concentrated nitric acid and concentrated sulfuric acid(catalyst) to form nitrobenzene and water

Question 11

why is sulfuric acid used in the nitration of benzene

Answer 11

the sulfuric acid is used a catalyst in the reaction, it helps form the nitronium ion which is the electrophile.

mechanism:
HNO3 + H2SO4 = HSO4^- + NO2^+ + H2O

Question 12

what is the uses of nitration reaction of benzene

Answer 12

• nitro compounds can be used to form aromatic compounds, these are used to make dyes and pharmaceuticals.
• nitro compounds decompose violently when heated, so they are used in explosives.

Question 13

what does friedel-crafts acylation do

Answer 13

it adds an acyl group to the to the benzene ring.

Question 14

explain how friedel-crafts acylation occur

Answer 14

the reactants are heated under reflux in a non aqueous solvent in the presence of a halogen carrier (catalyst) AlCl3 to from phenylketone and HCL.

Question 15

explain how a halogen carrier makes and electrophile stronger in the friedel-crafts acylcation

Answer 15

the ACl3 accepts a pair of lone electrons from the acyl chloride. as the pair of electrons is pulled away, the polarisation of the acyl chloride increases as it forms a carbocation. this give the elecrophile enough charge to react with the benzene.

it is the first step in the mechanism for the reaction

Question 16

how are amines and amides formed

Answer 16

they are formed from ammonia

Question 17

what is an amine and how is it formed

Answer 17

they are formed if one or more hydrogen form ammonia is replaced by an organic group such as an alkyl or aromatic compound, you get an amine

Question 18

explain the difference between a primary, secondary and tertiary amine

Answer 18

a primary amine has only one hydrogen replaced by and organic group, a secondary has two hydrogens that have been replaced by a organic group and a tertiary amine has had 3 hydrogens replaced by organic groups.

if another group is added, so you have 4 organic groups you get a quaternary amine ion that is postively charged

Question 19

how do you name an amine

Answer 19

you use the suffix amine/amine ion at for the end.
if all the organic groups are the same you add di - for secondary amines and tri- for tertiary amines
if the organic groups are different, you list the different groups in alphabetical order

Question 20

what are surfactants

Answer 20

they are compounds that are partially and partially insoluble in water

Question 21

what are cationic surfactants

Answer 21

they are surfactants that are postively charged.

Quaternary ammonium compounds can be used as cationic surfactants these are quaternary ammonium salts that have long hydrocarbon chains

Question 22

why are cationic surfactants useful as a detergent

Answer 22

this is because the long chain hydrocarbon is insoluble in water but will bind to non-polar substances such as grease and the polar head group will dissolve in water, allowing the grease to mix with the water and be washed away.

Question 23

how is cationic surfactants used in hair products and fabric conditioners

Answer 23

when hair or fabric gets wet they pick up negative charges on their surface. the positively charged part of the surfactant is attracted to the negatively charged surfaces and forms a coating over the surface. the coating prevents the build up of static electricity, it helps keep fabrics smooth and hair flat.

Question 24

why do amines act as weak bases

Answer 24

this is because they accept they accept protons

Question 25

what determines the strength of an amine as a base

Answer 25

the strength of a base is determined by how available the lone pair of electrons is on the nitrogen. the lone pair of electrons will be more available if the electron density is higher. the more available the lone pair of electrons is, the more likely the amine is to accept a proton, the stronger the base will be.

Question 26

are primary aromatic bases weak or strong

Answer 26

they are weak bases because the benzene ring draws electrons towards itself and the nitrogen’s lone pair gets partially delocalised onto the ring. therefore the electron density of the nitrogen decreases, this makes the lone pair of electrons less available.

Question 27

are primary aliphatic bases strong or weak bases

Answer 27

they are strong bases as they, this is because the alkyl group pushes electrons onto attached groups. so the electron density on the nitrogen increases, this makes the lone par more available

Question 28

what are the strength of ammonia as a base

Answer 28

the strength of ammonia lies somewhere inbetween. this is because the ammonia doesnt have an aromatic group to pull away the lone pair of electrons, or an alkyl group to push the lone pair of electrons forward.

Question 29

what functional group do amides have

Answer 29

they contain the functional group
-CONH2

Question 30

how do you name an amide

Answer 30

you use the suffix amide and the prefix of the acyl group

Question 31

what is an n-substituted amide

Answer 31

it is an amide where one of the hydrogen’s from the nitrogen is substituted with an acyl group

Question 32

how do you name an n-substituted amide

Answer 32

you add an N- at the front of the name followed by the alkyl group that has been added to the amide

Question 33

what are the two ways to form an amine

Answer 33

1- uses halogenalkanes in a nucleophilic substitution
2-it uses nitriles, this is done by reducing the nitrile using a strong reducing agent such as lithium aluminium hydride in dry ether, followed by some dilute acid

Question 34

what forms when you react acyl chloride react with ammonia

Answer 34

this forms primary amides, and then with primary amides to form n-substituted amides.