Alcohols, Alkenes, Organic Analysis

Question 1

Reactivity of Addition Polymers

Answer 1

• Polyalkenes only contain single bonds
• They are saturated
• The main carbon chain is non-polar
• This makes them unreactive.

Question 2

Electrophiles

Answer 2

• Electrophiles are electron pair acceptors
• attracted to regions of high density electron density
  (they are usually a positively charged ion or polar molecules)

Question 3

Properties of Polyalkanes

Answer 3

Intermolecular forces determine the properties of polyalkanes
- properties of polymers can be modified using plasticisers

Question 4

Primary, Secondary & Tertiary Alcohols

Answer 4

Primary alcohol: oxidise to aldehyde, lower boiling point / distilled off
- if heated under reflux, aldehyde does not evaporate off and gets further oxidised to a carboxylic acid.
Secondary alcohol: oxidised to ketone, no further oxidiation
Tertiary: resistant to oxidation, only oxidised by combustion

Question 5

Electrophilic addition w/Sulphuric acid

Answer 5

””
- sulphuric acid acts as a catalyst
-unsymmetrical alkeness form major & minor
- forms alkyl hydrogen sulphates
-hydrating them can form alcohols
- under 300 degrees & 60-70atms

Question 6

Bromine Water

Answer 6

Bromine water decolourises if an alkene is present
- this is electrophilic addition
equation: H2C=CH2 + Br2 –> CH2BrCH2Br

Question 7

Properties of Alcohols

Answer 7

R” - O’ - H” ( “ = partial +ve charge, ‘ = partial -ve charge)
- Alcohols are polar molecules
- The dipole allows for hydrogen bonding
- this makes alcohol:
- Soluble In Water - hydrogen bods form between the -OH
group in alcohols & H2O molecules
(however solubility decreases as length of the non-polar
carbon chain increases)
- Low Volatility - held together by strong hydrogen bonds,
high energy needed to cause vaporisation
- Less Acidic than water

Question 8

Elimination (alcohols)

Answer 8

• When alcohols are heated w/acid catalyst, a water molecule gets eliminated forming an alkene.
• If alcohol is unsymmetrical different alkenes form.
  products + being cis-trans isomers

Question 9

Major & Minor Products

Answer 9

• When an unsymmetrical alkene reacts with a hydrogen halide a major & minor product form.
• (Marhourimot Rule) i.e. hydrogen in Hhalide bond to carbon bonded to the highest no. of hydrogens.
• The dominating product depends on the stability of the carbocation formed.
• more stable - more alkyl groups
• because alkyl groups donate electrons to the positive charge making it more stable.

Question 10

Alcohol Production & Biofuels

Answer 10

Alkene hydration <- we can get an alkene from Cracking
Temp - 300°C
Pressure - 60 atm
Catalyst - Phosphoric Acid
Fermentation <- more sustainable anaerobic R -> C6H12O6 —-> 2C2H5OH(aq) + 2CO2(g)
Biofuels - fuels made from living material once its died

Carbon neutral – net-zero effect on the amount of CO2 in the atmosphere.
- fermentation process not carbon neutral due to emission during transportation (fossil fuels are still being used in process)
EQs:
C6H12O6 –> 2C2H5OH +2CO2 <- fermentation
2C2H5OH + 6O2 —> 4CO2 + 6H20 <- combustion
6CO2 + 6H2O –> C2H12O6 <- photosynthesis

Question 11

Dative/Co-ordinate Bond

Answer 11

• Shared pair of electrons donated by one atom only.

Question 12

Concentrated sulfuric acid is heated with a sample of butan-2-ol. A dehydration reaction occurs.
Draw the structures of the resulting organic products.

Answer 12

Question 13

Test for Ketones

Answer 13

Test: Tollen’s solution, Fehling’s solution and acidified potassium chromate (VI) solution.

Result: No reaction occurs with Tollen’s solution, Fehling’s solution or potassium chromate (VI) solution

Explanation: Ketones are not able to reduce the Ag+ ions, the Cu2+ ions or the Cr6+ ions.

Question 14

Test for Carboxylic acids without using carbonates

Answer 14

Three Solutions: Warming with acidified potassium chromate (VI), Tollen’s solution, Fehling’s solution.

Result: No reaction occurs with with Tollen’s solution, Fehling’s solution or potassium chromate (VI) solution

Explanation: Carboxylic acids are not able to be oxidised further.

Question 15

Test for Carboxylic acids using carbonates

Answer 15

Limewater: Add a carbonate and bubble the gas produced through limewater.

Result: Effervescence is produced and bubbling the gas through limewater makes it turn cloudy.

Explanation: Carboxylic acids are strong enough acids to liberate carbon dioxide from carbonate ions.

Question 16

fingerprint region

Answer 16

The fingerprint region is unique to each molecule, and can be used to identify a molecule by comparing it with known samples in databases.

Question 17

Test for Aldehydes

Answer 17

Test 1 – Tollen’s Reagent: Warm aldehyde with Tollen’s reagent.

Result: Silver mirror is formed on the inside of the test tube.

Test 2 – Fehling’s Reagent: Warm aldehyde with Fehling’s solution which is a blue solution.

Result: The blue solution produces a brick red precipitate.

Question 18

Identifying Alcohols

Answer 18

Test: Warm with orange acidified potassium dichromate (VI) solution

Result: The orange solution turns green with primary and secondary alcohols, but stays orange (no reaction) with tertiary alcohols.

Question 19

Test for alkenes and alkanes

Answer 19

Test: Add bromine water which is an orange solution

Result: If a double bond is present in the molecule, as there is in alkenes, the orange solution turns colourless. If there is no double bond, as in alkanes, there is no reaction, so the solution remains orange.

Question 20

Test for Halogenoalkanes

Answer 20

Warm with dilute sodium hydroxide solution.
Add acidified (nitric acid) silver nitrate solution
Add dilute ammonia solution
Add concentrated ammonia solution

Question 21

mechanism for propan-2-ol + hot concentrated sulfuric acid

Answer 21

Question 22

C = C <- A C= O <- B
Which of the above can be reduced and why?

Answer 22

• B
• Can’t be C=C because it has no partial positive charge for nucleophiles to be attracted to.
• The high electron density will repel the nucleophile.
• The C=O has a partially positive carbon so hydrogen ions will be attracted.

Question 23

What is the origin of E/Z isomers of a molecule?

Answer 23

Lack of free rotation around C=C bond
/
restricted rotation around C=C double bond