amines

Question 1

Why are aromatic amines less basic

Answer 1

as benzene rings are electron withdrawing groups so they pull electrons away from the nitrogen. This means that electron density at the nitrogen decreases so lone pair availability decreases so aromatic amines are less basic.

Question 2

why is ammonia not too basic

Answer 2

as the nitrogen has 3 hydrogens attached to it so electrons are spread equally at the nitrogen, electron density is equal so lone pair availability isnt affected too much

Question 3

why are primary aliphatic or secondary aliphatic amines more basic
why are tertiary aliphatic amines not as basic as secondary or primary eventhough they have more alkyl groups

Answer 3

as alkyl groups are electron pushing groups, these push electrons towards the nitrogen, this means that electron density at the nitrogen increases so the lone pair availability increases this makes aliphatic amines more basic.
as the tertiary one isnt as stable as the secondary amine

Question 4

justify the statement that it is better to prepare primary amines from nitriles rather than from haloalkanes

Answer 4

with haloalkanes, further reactions can occur to produce secondary or tertiary amines, so impure products.
with nitriles, no further reactions occur and higher atom economy

Question 5

a student dissolves a few drops of propylamine in 1cm3 of water in a test tube. give an equation for the reaction that occurs, describe what is observed when universal indicator is added to this solution

Answer 5

ch3ch2ch2ch2nh2 + h20—> ch3ch2ch2nh3+ + oh-

green turns blue

Question 6

nitrobenzene reduction, why is an aqueous solution obtained eventhough phenyl amine is insoluble in water

Answer 6

as the phenyl amine is present as an ammonium salt, phenyl ammonium chloride.

Question 7

how can an infrared tell apart a secondary and tertiary amine

Answer 7

a primary one would have the absorption at the N-H bond however the tertiary one wouldnt as the n is attached to other groups not the hydrogen.

Question 8

ch3ch2br to ch3ch2ch2nh2- 2 step process. reagent conditions and diasdv

Answer 8

2 step- add kcn and add h2
kcn= ethanolic or aq
intermediate made= propane nitrile
then add h2, ni catalyst
disadv= kcn is toxic and h2 flammable

Question 9

ch3ch2ch2br to ch3ch2ch2nh2- 1 step process

Answer 9

excess nh3

further reactions can occur due to lone pair on n= impure product.

Question 10

amines E F and G are weak bases, explain the diff in base strength of these 3 amines and order of increasing base strength
e= phenyl amine
f= ethyl amine
g=secondary amine ethyl

Answer 10

strength depends on the availabilty of lone pairs on the nitrogen atom
for e, it is next to the ring so delocalised into ring so less lone electrons available
f or g= next to alkyl so positive inductive effect more electrons pushed onto the n so more lone pairs available
f has mroe alkyl groups next to it

so order= f,g,e with f being the most basic and e being the least basic

Question 11

amine f= secondary amine phenyl and then nhch2ch3 can be made in a 3 step process starting from methylbenzene suggest the structures of the two intermediate compounds. for each step give reagents and conditions

Answer 11

c6h5cl = conditions. cl2 and uv

c6h5ch2cn= kcn alcoholic and aq
step 3- h2 with ni catalyst