MO7 Bases, Alcohols And Thiols

Question 1

Define a base

Answer 1

• proton acceptor
• forms conjugate acid
• has a lone pair of electrons (or -ve charge) that can accept a proton

Question 2

Explain how pKa relates to a base

Answer 2

The pKa values of basic functional groups refers to the acidity of the conjugate acid (protonated form) of a base.

Question 3

Why are amines reactive and why is the amine salt more commonly used in formulation?

Answer 3

• amines are reactive as gathering have a lone pair of e- so can act as a nucleophile
• the amine salt is more often used as it is easier to handle (powder while free amine is oil), more stable and less reactive,
  Has better water solubility and is not as volatile and has a higher boiling point than free amines

Question 4

What are the properties of aliphatic amines?

Answer 4

• basic
  -pKa of 9-11
• classified 1, 2, 3* or 4* based on how many substituents are attached to N

Question 5

What are the properties of an aromatic amine?

Answer 5

• one or more direct N-substituents attached to an aromatic ring
  -pKa of 3-5, only weakly basic.
• lone pair of e- are stabilised by delocalisation into the ring, not a good base

Question 6

If amines are polar, why are they bases not acids?

Answer 6

The conjugate base is not favourable to form

Question 7

What are the properties of an imine?

Answer 7

-pKa 3.4
- N= in a ring
-much weaker base than an aliphatic amine

Question 8

What is an alcohol?

Answer 8

• hydroxyl group (-OH) bonded to saturated carbon
• O has 2 pairs of non bonding electrons
• classified based on substituents on adjacent C.
  -polar, so good at H bonding

Question 9

What is a thiol?

Answer 9

• a SH group
• stronger nucleophile and more acidic than alcohols