Lectures 2 and 3: Functional Groups

Question 1

What is a heteroatom?

Answer 1

An atom other than carbon or hydrogen that is found in organic molecules.

Question 2

What are the a) oxygen-based, b) nitrogen-based and c) sulphur-based functional groups?

Answer 2

a) Alcohol (hydroxyl), ether (alkoxyl), carbonyl, ester
b) amino, imino, amide
c) thiol, thioester, thioester

Question 3

What is the shape, hybridisation and reactivity of alcohols?

Answer 3

Shape: tetrahedral
Hybridisation: sp3
Reactivity: nucleophile and base

Question 4

What is the shape, hybridisation and reactivity of ethers?

Answer 4

Shape: tetrahedral
Hybridisation: sp3
Reactivity: unreactive, poor nucleophile

Question 5

What is the shape, hybridisation and reactivity of aldehydes and ketones?

Answer 5

Shape: planar, polarised bond
Hybridisation: sp2
Reactivity: reactive electrophilic carbon

Question 6

What is the shape, hybridisation and reactivity of carboxylic acids?

Answer 6

Shape: planar
Hybridisation: sp2
Reactivity: sp2 hybridisation of O promotes delocalisation of lone pair, dissociates readily to form conjugate base.

Question 7

What is the shape, hybridisation and reactivity of esters?

Answer 7

Shape: planar
Hybridisation: sp2
Reactivity: less reactive than aldehydes/ketones, because lone pair dissociates into double bond, reducing the electrophilicity of the carbonyl carbon

Question 8

What are good biological nucleophiles?

Answer 8

Hydroxyl groups (alcohols), thiols

Question 9

What are good biological electrophiles?

Answer 9

The carbon in a carbonyl (aldehyde or ketone), imine or thioester

Question 10

What’s the difference between a nucleophile and a base?

Answer 10

A base nucleophilically attacks a proton, whereas a nucleophile nucleophilically attacks any atom other than hydrogen (mostly carbon in biological systems).

Question 11

Which functional groups have a lone pair dissociating into the double bond?

Answer 11

Esters
Carboxylic acids
Amides

Question 12

What is the shape, hybridisation and reactivity of amines?

Answer 12

Shape: tetrahedral
Hybridisation: sp3
Reactivity: lone pairs, electronegativity, nucleophile, base (not when protonated to NH3+)

Question 13

What is the shape, hybridisation and reactivity of amides?

Answer 13

Shape: planar
Hybridisation: sp2
Reactivity: Nitrogen is not a nucleophile, not a base, because delocalisation of the lone pair on N into C=O double bond reduces the electrophilicity of the carbonyl carbon, less reactive than aldehydes/ketones.

Question 14

What is the shape, hybridisation and reactivity of imine?

Answer 14

R-(C=N-R)-R
Shape: planar
Hybridisation: sp2
Reactivity: very electrophilic carbon, strongly polarised bond due to electronegativity of nitrogen (nitrogen equivalent of aldehyde/ketone)

Question 15

What is the shape, hybridisation and reactivity of thiols?

Answer 15

Shape: tetrahedral
Hybridisation: sp3
Reactivity: very nucleophilic, more nucleophilic than alcohol, because its lone pairs are very polarisable (level 3 electrons). Orbitals too big for effective overlap with hydrogen so no hydrogen bonding. Not basic. Can be oxidised to S-S bridge.

Question 16

What is the shape, hybridisation and reactivity of thioesters?

Answer 16

Shape: planar
Hybridisation: sp3
Reactivity: very reactive because its orbitals are too big to overlap with the pz orbitals of the C=O bond, so the carbonyl carbon is very electrophilic. Thiol is an excellent leaving group.

Question 17

What is the shape, hybridisation and reactivity of thioethers?

Answer 17

Shape: tetrahedral
Hybridisation: sp3
Reactivity: more reactive than ether, can be oxidised to sulphoxide and sulphone using 3d orbitals

Question 18

Give an example of a functional group that has resonance hybrids.

Answer 18

Amide

R-(C=O)-NH2 –> R-(C-O-)=N+H2