ORGANIC CHEMISTRY- amines

Question 1

draw the structure of a primary, secondary, tertiary amines and quaternary ammonium ions.

Answer 1

pmt

Question 2

how do you name amines?

Answer 2

prefix - amino
suffix - amine

Question 3

why are amines so reactive?

Answer 3

the lone pair of electrons on the Nitrogen, due to polar N-H bond

Question 4

what shape is amine around the N? bond angle?

Answer 4

trigonal pyramidal
107 degrees

Question 5

what kind of intermolecular forces do they have?

Answer 5

hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom

Question 6

do amines have intermolecular forces stronger or weaker than alcohols?

Answer 6

Weaker as N has lower electronegativity than O = weaker hydrogen bonding

Question 7

what state are amines at 298K?

Answer 7

short chains = gases
longer chains = volatile liquids

Question 8

smell of amines?

Answer 8

fishy/rotting smell

Question 9

which primary amines are soluble in water/alcohols? why?

Answer 9

• up to 4 C atoms
• can hydrogen bond to water molecules
• after this non polarity of hydrocarbon chain can make them insoluble

Question 10

what kinds of solvents are amines soluble in?

Answer 10

less or non polar solvents

Question 11

what is the solubility of phenyl amine? why?

Answer 11

• not soluble = due to non polarity of benzene ring C6H5 = cannot form hydrogen bonds

Question 12

when do amines act as bases?

Answer 12

when they bond with a H+ ion

Question 13

how can amines act as nucleophiles?

Answer 13

lone pair from N is donated to electron deficient carbon

Question 14

draw a mechanism for the basic action of an amine with water?

Answer 14

pmt

Question 15

what is the product from basic action of an amine with water?

Answer 15

RNH3+ - ammonium ion = forms a salt with an anion

Question 16

is ammonium ion soluble in water? why?

Answer 16

yes, it is ionic so attracted to polar bonds on H2O

Question 17

how can you regenerate soluble amine from ammonium salt?

Answer 17

add NaOH ( strong base) = removes H+ ions from ammonium ion

Question 18

In order to be the strongest base, what must a particular amine have?

Answer 18

• greatest electron density around the N atom, making it a better electron pair donor ( attracts protons more)

Question 19

what does positive/ negative inductive effect mean?

Answer 19

positive = donate electrons
negative= remove electrons

Question 20

what effect do alkyl groups have on electron density and base strength?

Answer 20

positive inductive effect = increase electron density around the N = stronger base

Question 21

what effect do aryl groups have on electron density and base strength?

Answer 21

negative inductive effect = decrease electron density around N = lone pair of electrons are lost to delocalised electron ring so less electrons are available to share = weaker base

Question 22

why are tertiary amines never good bases?

Answer 22

they are insoluble in water

Question 23

place in order of base strength: NH2, primary amine, secondary amine, phenylamine

Answer 23

secondary amine > primary amine > NH3 > phenylamine

Question 24

draw a mechanism for the nucleophilic substitution of NH3 with RCH2Br to form primary amines?

Answer 24

pmt

Question 25

how can primary amines then form secondary, tertiary amines and quaternary ammonium ions ?

Answer 25

multiple substitutions : primary amine is a nucleophile that attacks the original haloalkane

Question 26

how do you prepare aliphatic amines?

Answer 26

1. halogen alkanes are reacted with an excess of concentrated ammonia dissolved in ethanol at pressure in a sealed container

(nucleophilic substitution method)

2. reduction of nitrile compounds = formation of nitrile from halogenalkanes, reduction of nitrile to form amine (LiAlH4 + ethanol as solvent, Ni catalyst)

Question 27

why is reduction of nitrile a purer method?

Answer 27

only the primary amine can be formed

Question 28

what are the problems with this method?

Answer 28

not efficient as low yield of primary amines due to multiple substitutions

Question 29

how do you prepare aromatic amines?

Answer 29

reduction of nitro compounds using tin and concentrated HCl , then add NaOH

Question 30

what conditions are needed to form nitrobenzene from benzene?

Answer 30

conc H2SO4 and HNO3 to form NO2+ ions for electrophilic attack

Question 31

how do you form an ammonium chloride salt from nitrobenzene? what conditions are needed?

Answer 31

reduce the nitrile using tin = forms an ammonium salt with Cl- ions
Room temp

Question 32

equation for the reaction of nitrobenzene to phenylamine?

Answer 32

C6H5NO2 + 6[H] –> C6H5NH2 + 2H2O

Question 33

what mechanism is used to form amides from acyl chlorides and amines?

Answer 33

nucleophilic addition-elimination

Question 34

in which industries are amines used?

Answer 34

dyes,drugs

Question 35

what are cationic surfactants?

Answer 35

quaternary ammonium salts, with a cation that is charged at one end and non-polar at the other.

Question 36

how do cationic surfactants work in fabric/ hair conditioners?

Answer 36

negative charges on the surface of the fabric/ hair are attracted to the cation, removing them from the surface = prevents build up of static electricity and keeps hair flat and fabric smooth

Question 37

how do cationic surfactants sit when placed in water?

Answer 37

charged end in water, non polar end sticking out of water/ at the surface.