nitrogen compounds

Question 1

why do primary and secondary amines have higher boiling points than tertiary amines?

Answer 1

1. tertiary amines have no N-H bond, and are unable to form hydrogen bonds
2. their molecules are held together by weak pdpd interactions which require less energy to overcome as compared to stronger hydrogen bonds between molecules of primary and secondary amines

Question 2

why are phenylamines and amines insoluble in water

Answer 2

1. the energy released from hydrogen bonding formed between these amines with water is less able to overcome the energy required to overcome the increasing length of dispersion forces between larger hydrocarbon chains, and the existing hydrogen bonding in water

Question 3

how can amines function as bases

Answer 3

1. amines contain a lone pair of electrons on the nitrogen atom that can form a coordinate bone with a proton
2. amins can also act as lewis bases by donating its electron pair to an acid

Question 4

why are aliphatic amines more basic than ammonia in the gaseous phase

Answer 4

1. aliphatic amines contain alkyl groups which are electron donating
2. this increases the electron density on the nitrogen atom, making the lone pair of electrons more available to form a dative bond

Question 5

why are phenylamines less basic than ammonia in the gaseous phase

Answer 5

1. the lone pair of electrons on nitrogen is delocalised into the bezene ring
2. this decreases the electron density on the nitrogen atom, making the lone pair of electrons less available to form a dative bond with a proton

Question 6

why do amides give neutral solutions in water

Answer 6

1. the delocalisation of the lone pair of electrons on the nitrogen atom over the C=O bond reduces the electron density on the nitrogen atom such that the lone pair of electrons on the nitrogen atom is not available for protonation

Question 7

reagents and conditions for preparation of phenylamine from nitrobenzene

Answer 7

1. Sn, concentrated HCl, heat
2. NaOH

Question 8

reagents and conditions of reaction of amines with acids

Answer 8

1. mineral acids or carboxylic acids, RTP
2. amines can be regenerated via use of strong bases

Question 9

reagents, conditions and observations for electrophilic substitution of phenylamine with aqueous bromine

Answer 9

1. aqueous bromine, RTP
2. yellow-orange solution decolourise, white ppt formed

Question 10

reagents and conditions of reduction of amides

Answer 10

1. LiAlH4 in dry ether

Question 11

reagents and conditions for hydrolysis of amides

Answer 11

1. acidic: dilute H2SO4, heat under reflux
2. alkaline: dilute NaOH, heat under reflux followed by acidification
3. ammonia will be produced if the primary amides undergo alkaline hydrolysis

Question 12

predominant species of an amino acid in aqeuous solutions of different pH

Answer 12

1. at a very low pH, the amino group would be protonated, hence the amino acids exists predominantly as a cation
2. at a very high pH, the carboxylic acid group would be deprotonated, hence the predominant species is an anion
3. at neutral pH, the amino acid would exist as a zwitterion