Organic Nitrogen Test

Question 1

Boiling point trend in amines

Answer 1

• Boiling points increase with molecular mass. • Amines have higher boiling points than corresponding alkanes because of intermolecular hydrogen bonding.

Question 2

Solubility of amines

Answer 2

• Soluble in organic solvents. • Lower mass compounds are soluble in water due to hydrogen bonding with the solvent. • Solubility decreases as molecules get heavier.

Question 3

Why are amines bases?

Answer 3

The lone pair on nitrogen makes amines basic. RNH2 + H+—> RNH3+

Question 4

Strength of bases in amines

Answer 4

• depends on the availability of the lone pair and thus its ability to pick up protons• the greater the electron density on the N, the better its ability to pick up protons• this is affected by the groups attached to the nitrogen.

Question 5

What decreases basicity of amines?

Answer 5

Electron withdrawing substituents (e.g. benzene rings) decrease basicity as the electron density on N is lowered.

Question 6

What increases basicity of amines?

Answer 6

Electron releasing substituents (e.g. CH3 groups) increase basicity as the electron density is increased

Question 7

The strength of a weak base is depicted by what?

Answer 7

the strength of a weak base is depicted by its Kb or pKb value• the larger the Kb value the stronger the base• the smaller the pKb value the stronger the base.• the pKa value can also be used - ( pKa + pKb = 14 )• the smaller the pKb, the larger the pKa.

Question 8

Amines which dissolve in water produce…

Answer 8

Weak alkaline solutionsCH3NH2(g) + H2O(l) –> CH3NH3(aq) + OH+

Question 9

Amines react with acids to produce…

Answer 9

SaltsC6H5NH2(l) + HCl(aq) —> C6H5NH3+ClAddition of aqueous sodium hydroxide liberates the free base from its saltC6H5NH3+Cl ̄(aq) + NaOH(aq) —> C6H5NH2(l) + NaCl(aq) + H2O(l)

Question 10

Due to their lone pair, amines react as nucleophiles with…

Answer 10

• haloalkanes forming substituted amines- nucleophilic substitution• acyl chlorides forming N-substituted amides- addition-elimination

Question 11

Amines can be prepared from haloalkanes

Answer 11

Reagent Excess, alcoholic ammoniaConditions Reflux in excess, alcoholic solution under pressureProduct Amine (or its salt due to a reaction with the acid produced)Nucleophile Ammonia (NH3)Equation C2H5Br + NH3 (aq / alc) ——> C2H5NH2 + HBr

Question 12

Why excess ammonia with amines prepared from haloalkanes?

Answer 12

The amine produced is also a nucleophile and can attack another molecule of haloalkane to produce a secondary. This in turn can react further producing a tertiary amine and, eventually an ionic quarternary amine. By using excess ammonia, you ensure that all the haloalkane molecules react with ammonia rather than the newly produced haloalkane.

Question 13

Amino acids contain what two functional groups.

Answer 13

• amine NH2• carboxyl COOH

Question 14

Amino acids can exist as optical isomers if they have different R1 and R2 groups

Answer 14

• optical isomers exist when a molecule contains an asymmetric carbon atom• asymmetric carbon atoms have four different atoms or groups attached• two isomers are formed• one rotates plane polarised light to the left, one rotates it to the right• no optical isomerism with glycine - two H’s are attached to the C atom

Question 15

What is a zwitterion?

Answer 15

• a zwitterion is a dipolar ion• it has a plus and a minus charge in its structure• a proton from the COOH group moves to NH2• amino acids exist as zwitterions at a certain pH• the pH value is called the isoelectric point• produces increased inter-molecular forces• melting and boiling points are higher

Question 16

Acidic/basic properties of amino acids.

Answer 16

• amino acids possess acidic and basic properties due to their functional groups• they will form salts when treated with acids or alkalis.

Question 17

How are peptides formed?

Answer 17

α-amino acids can join up together to form peptides via an amide or peptide link• 2 amino acids joined dipeptide• 3 amino acids joined tripeptide• many amino acids joined polypeptide

Question 18

Peptides can be broken down into their constituent amino acids by…

Answer 18

Hydrolysis• attack takes place at the slightly positive C of the C=O• the C-N bond next to the C=O is broken• hydrolysis with just water is not feasible• hydrolysis in alkaline/acid conditions is quicker• hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts

Question 19

What are proteins?

Answer 19

• polypeptides with high molecular masses• chains can be lined up with each other• the C=O and N-H bonds are polar due to a difference in electronegativity• hydrogen bonding exists between chains

Question 20

Structure of amides

Answer 20

Based on a carboxylic acid (remove OH, add NH2)

Question 21

Appearance of amides

Answer 21

White crystalline solid

Question 22

Nomenclature of amides

Answer 22

Named from the corresponding acid (remove oic acid… add amide)

Question 23

Preparation of amides

Answer 23

Acyl chloride + ammonia (or amines for 2° amides)e.g. CH3COCl(l) + NH3(aq) —> CH3CONH2(s) + HCl(g)

Question 24

Hydrolysis of amides

Answer 24

general reaction: CH3CONH2 + H2O —> CH3COOH + NH3acidic soln.: CH3CONH2 + H2O + HCl —> CH3COOH + NH4Clalkaline soln.: CH3CONH2 + NaOH —> CH3COONa + NH3

Question 25

Identification of amides

Answer 25

Warming with dilute sodium hydroxide solution and testing for the evolution of ammonia using moist red litmus paper is used as a simple test for amides.

Question 26

Reduction of amides

Answer 26

Reduced to primary amines:CH3CONH2 + 4[H] ——> CH3CH2NH2 + H2O

Question 27

What is the simplest amine?

Answer 27

Ammonia

Question 28

Aromatic amines have…

Answer 28

The N joined directly to the benzene ring.

Question 29

Quaternary ammonium salts contain…

Answer 29

Quaternary ammonium ions and are related to amines, but they are not amines and do possess a lone pair of electrons on the N.

Question 30

Quaternary ammonium salts with some long chain alkyl groups are used as…

Answer 30

Cationic detergents.

Question 31

Reduction of nitrile compounds to form amines

Answer 31

This is the commonest way and is usually done in twosteps:a) producing a nitrile compound from a haloalkaneb) then reducing the nitrile compound

Question 32

What is the stronger base out of methylamine and diethylamine?

Answer 32

Diethylamine- diethylamine is 2y amine whereas methylamine is 1y amine; ∴ more electron density pushed onto N lone pair in diethylamine ∴ diethylamine better at accepting H+

Question 33

What is the stronger base out of propylamine and phenylamine?

Answer 33

Propylamine- propylamine is 1y amine whereas phenylamine is aromatic amine; ∴ more electron density pushed onto N lone pair in propylamine (in phenylamine electron density is delocalised into the ring away from the N) ∴ propylamine better at accepting H+

Question 34

What is the stronger base out of ammonia and phenylmethylamine?

Answer 34

Phenylmethylamine- phenylmethylamine is 1y∴ more electron density pushed onto N lone pair in phenylmethylamine ∴ phenylmethylaminebetter at accepting H+ amine compared to ammonia

Question 35

What is the stronger base out of ammonia and cyclohexylamine?

Answer 35

Cyclohexylamine- cyclohexylamine is 1 amine compared to ammonia ∴ more electron density pushed onto N lone pair in cyclohexylamine ∴ cyclohexylamine better at accepting H+

Question 36

In general, the order of base strength is:

Answer 36

tertiary > secondary > primary > NH3 > aromatic

Question 37

3y,2y,1y amines compared to ammonia

Answer 37

• Compared to ammonia, the more alkyl groups that are substituted onto the N atom in place of H atoms, the more electron density is pushed onto the N atom (as the inductive effect of alkyl groups is greater than that of H atoms -so alkyl groups push electron density towards the N atom better than H atoms). • So the more alkyl groups, the higher the electron density of the lone pair on the N, so the stronger the base.

Question 38

Aromatic amines compared to ammonia

Answer 38

• The lone pair on this N is partially delocalised into the benzene ring, leading to a reduction in the electron density on the N atom, so weaker base strength.

Question 39

acid/base reactions of amino acids…with acids

Answer 39

with acidsreagents: HClconditions: room temperatureequation: R-CH(NH2)-COOH + HCl —> R-CH(NH3+Cl-)-COOH

Question 40

acid/base reactions of amino acids…with alkalis

Answer 40

with alkalisreagents: NaOHconditions: room temperatureequation: R-CH(NH2)-COOH + NaOH —> R-CH(NH2)-COO-Na+ + H2O