Organic Chemistry I

Question 1

Which alcohols make carboxylic acids when oxidised?

Answer 1

Primary Alcohols

Question 2

Which alcohols make ketones when oxidised?

Answer 2

Secondary Alcohols

Question 3

What 4 reactions can alcohols do?

Answer 3

Combustion
Halogenation
Oxidation
Elimination

Question 4

Describe the solubility of alcohols.

Answer 4

• alcohols are miscible in water because of the O-H group
• this depends on the length of the non-polar part of the hydrocarbon
• however longer hydrocarbon chains decrease solubility as they cannot hydrogen bond with water

Question 5

What is a primary, secondary, and tertiary alcohol?

Answer 5

• primary alcohols are bonded to a carbon that is bonded to 1 other carbon
• secondary alcohols are bonded to a carbon that is bonded to 2 other carbons
• tertiary alcohols are bonded to a carbon that is bonded to 3 other carbons

Question 6

What happens in the combustion of alcohols?

Answer 6

Alcohols burn to produce CO2 and H2O (if its complete)

Question 7

What happens in chlorination of alcohols?

Answer 7

PCl5 is added to the alcohol, where any OH’s will be replaced by Cl.
e.g. PCl5 + C2H5OH -> C2H5Cl + POCl3 + HCl

• the POCl3 must be separated from the product using fractional distillation and the HCl will produce misty fumes

Question 8

What conditions must chlorination take place under?

Answer 8

• with dry ether (anhydrous conditions)
• because PCl5 will react with water

Question 9

Are primary or tertiary alcohols easier to chlorinate and why? (visualise)

Answer 9

• tertiary are easier
• because tertiary are more reactive
• the CH3 groups push e- towards the central carbon and there fore weaken the C-O bond
• so the O will fall off more easily

Question 10

What happens in bromination of alcohols?
This is a TWO STEP reaction.

Answer 10

• add a mixture of KBr and concentrated H2SO4 to the alcohol
  1. KBr + H2SO4 -> KHSO4 + HBr
  2. HBr + C2H5OH -> C2H5Br + H2O

This is a nucleophilic substitution reaction.

Question 11

What happens in iodination? This is a TWO STEP reaction.

Answer 11

• add a mixture of red phosphorus and iodine
• then heat under reflux
  1. 2P + 3I2 -> 2PI3
  2. 3C2H5OH + PI3 -> 3C2H5I + H3PO3

Question 12

What conditions are needed for the elimination of alcohol? (aka dehydration)

Answer 12

• heat with concentrated phosphoric (V) acid
• OR heat with NaOH/KOH in ethanolic solution
• this makes alkenes