Functional group chemistry 7&8 - amides Flashcards
1
Q
What are amides?
A
carbonyl compounds substituted by an atom more electronegative
(and therefore more basic) than carbon.
2
Q
Describe the stability of amides.
A
- very unreactive; do not react with water, alcohols, carboxylate ions, halide ions; incoming nucleophile is a weaker base than the leaving group
- More stable chemically and in vivo than esters; metabolic hydrolysis can occur via amides enzymes
- Lone pair on nitrogen is stabilised due to resonance
- Proteins are composed of amino acids linked together by amide bonds
3
Q
Describe the properties of amides.
A
- Neutral
- Boiling points: amides with equivalent heavy atoms have significantly higher boiling points + BP of liquids increase as the intermolecular forces between the molecules of that solvent increase in strength - hydrophobic interactions in hydrocarbons, pi stacking in aromatics and H bonding in alcohols
- Both H bonding and strong dipole/charge interactions increases boiling point
4
Q
Describe the structure of an amide.
A
- Has 4 electrons shared between 3 pi orbitals
- Nitrogen is planar with electron pair in a ‘p’ orbital - sp2 hybridised
- Electrons shared unequally - greater electron density on the oxygen
- With orbital overlap imparting partial double bond character to the amide bond
5
Q
How does the solvent effect the rate of rotation ?
A
- Fastest in the least polar solvent
- Solvents like water and DMSO have strong dipole moment and interacts with organic molecules
- Charges and dipoles help bring molecules together
6
Q
Protonation - what allows resonance stabilisation of amides?
A
Electron overlap from nitrogen lone pair
7
Q
Why does protonation on nitrogen not occur?
A
It destroys resonance stabilisation
8
Q
What allows resonance stabilisation of cation?
A
Protonation on oxygen
9
Q
How can amides be made?
A
- Thionyl Chloride
- PCl5
- Acid Anhydrides
10
Q
How can we get direct amide formation?
A
- From an ester
- From an acid
11
Q
A
