Alcohols, Alkenes, Organic Analysis Flashcards
Reactivity of Addition Polymers
- Polyalkenes only contain single bonds
- They are saturated
- The main carbon chain is non-polar
- This makes them unreactive.
Electrophiles
- Electrophiles are electron pair acceptors
- attracted to regions of high electron density
(they are usually a positively charged ion or polar molecules)
Properties of Polyalkanes
Intermolecular forces determine the properties of polyalkanes
- properties of polymers can be modified using plasticisers
Primary, Secondary & Tertiary Alcohols
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
Electrophilic addition w/Sulphuric acid
””
- 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
Bromine Water
Bromine water decolourises if an alkene is present
- this is electrophilic addition
equation: H2C=CH2 + Br2 –> CH2BrCH2Br
Properties of Alcohols
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
Elimination (alcohols)
- 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
Major & Minor Products
- 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.
Alcohol Production & Biofuels
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
Dative/Co-ordinate Bond
- Shared pair of electrons donated by one atom only.
Concentrated sulfuric acid is heated with a sample of butan-2-ol. A dehydration reaction occurs.
Draw the structures of the resulting organic products.
Test for Ketones
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.
Test for Carboxylic acids without using carbonates
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.
Test for Carboxylic acids using carbonates
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.
fingerprint region
The fingerprint region is unique to each molecule, and can be used to identify a molecule by comparing it with known samples in databases.
Test for Aldehydes
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.
Identifying Alcohols
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.
Test for alkenes and alkanes
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.
Test for Halogenoalkanes
Warm with dilute sodium hydroxide solution.
Add acidified (nitric acid) silver nitrate solution
Add dilute ammonia solution
Add concentrated ammonia solution
mechanism for propan-2-ol + hot concentrated sulfuric acid
C = C <- A C= O <- B
Which of the above can be reduced and why?
- 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.
What is the origin of E/Z isomers of a molecule?
Lack of free rotation around C=C bond
/
restricted rotation around C=C double bond
