module 4.2 - core organic chemistry: alcohols, haloalkanes and analysis

Question 1

properties of alcohols
- solubility
- polarity
- volatility

Answer 1

• OH bond is polar: difference in polarity
• alcohols aren’t as volatile as the alkanes cause of the forces between molecules
• hydrogen bonding between alcohol molecules mean: higher bpt, solubility in water
• alcohols = miscible (soluble) in water
• hydrogen bonds between the alcohol molecules can break and re-form with water molecules

Question 2

what reactions will an alcohol undergo

Answer 2

• combustion
• oxidation
• elimination
• substitution

Question 3

oxidation of alcohols require …

Answer 3

an oxidation agent

Question 4

what is the oxidation agent

Answer 4

acidified potassium dichromate H+/Cr2O7 2-

Question 5

what does the oxidation/reflux of a primary alcohol produce
+ equations

(R = alkyl, alicyclic or aromatic)

Answer 5

aldehydes -> carboxylic acid
RCH2OH + [O] -> RCHO + H2O
RCHO + [O] -> RCOOH
RCH2OH + 2[O] -> ROOH + H2O

Question 6

what does the oxidation/reflux of a secondary alcohol produce
+ equations

(R = alkyl, alicyclic or aromatic)

Answer 6

ketone
RCH(OH)R + [O] -> RCOR + H2O

Question 7

what does the oxidation/reflux of a tertiary alcohol produce
+ equations

Answer 7

nothing - tertiary alcohols are resistant to oxidation

Question 8

observations whilst heating primary, secondary and tertiary alcohols under reflux

Answer 8

primary = orange -> dark green
secondary = orange -> dark green
tertiary = no colour change (stays orange)

Question 9

what does the distillation of a secondary alcohol produce

Answer 9

aldehyde

Question 10

2 types of reactions that alcohols undergo
(halides and H2O)

Answer 10

substitution (H2O) - example of nucleophilic substitution
elimination (halide)

Question 11

substitution reactions - alcohols

Answer 11

• can undergo substitution reactions with halide ions, in the presence of acid to form haloalkanes

CH3CH2OH + X- -> CH3CH2X + OH-
( X replaces OH)

Question 12

elimination reactions - alcohols

Answer 12

CH3CH2OH -> CH2CH2 + H2O

Question 13

conditions needed for dehydrating alcohols (elimination reaction)

Answer 13

• heating to 170 degrees
• excess of concentrated sulphuric acid/phosphoric acid
• reaction can be done with aluminium oxide catalyst (Al2O3)

Question 14

what is a haloalkane

Answer 14

hydrocarbon where one H has been replaced with a halogen

Question 15

what reaction does a haloalkane undergo

Answer 15

substitution

Question 16

substitution reactions of haloalkanes

Answer 16

• X atom (halide) replaced by incoming group/nucleophile
• because C-X bond is polar. C atom is slightly positively charged and open to attack

Question 17

hydrolysis of haloalkanes
+ equation

Answer 17

• primary alcohols are heated under reflux with an aqueous solution of an alkali
• hydrolysed to a primary alcohol
  CH3CH2Br + NaOH -> CH3CH2OH + NaBr
  (OH replaces Br)

Question 18

nucleophile definition

Answer 18

electron pair donor

Question 19

rate of hydrolysis of haloalkanes trend

Answer 19

hydrolysis of chlorobutane = slowest
hydrolysis of iodobutane = fastest

tertiary haloalkanes = easiest to hydrolyse
primary haloalkanes = hardest to hydrolyse

Question 20

explanation of difference in rate of hydrolysis

Answer 20

• the weaker the bond is, the easier it is to lose the X
• C-F bond doesn’t undergo nucleophilic substitution