ORGANIC CHEM Flashcards
How E/Z Isomers Arise
Each C atom in the C=C double bond is bonded to two different groups
There is restricted rotation around the C=C double bond
Why is there no rotation around a C=C double bond?
• The π bond is formed by overlap of p orbitals
• If there was any rotation, the p orbitals would no longer overlap and the π
bond would break
Why are tertiary carbocations more stable than primary carbocations?
•There is a positive inductive effect from three alkyl groups in 3° carbocations compared to two alkyl groups in 2° carbocations
Explain why 2-bromo propane is the major product in this reaction.
• 2-bromopropane is made from a secondary carbocation
• 1-bromopropane is made from a primary carbocation
• Secondary carbocations are more stable than primary carbocations due to the
positive inductive effect of the two alkyl groups (compared to one)
Why is distillation used when producing an aldehyde from a primary alcohol?
• Distillation allows the aldehyde to escape the reaction mixture and prevents further oxidation
What happens to the aldehyde as it is produced during distillation?
The aldehyde forms as a vapour and escapes from the reaction mixture into the condenser
Ethanol can be oxidised to ethanal or ethanoic acid. Describe how ethanal can be made in high yield, as opposed to ethanoic acid.
Use distillation
• Heat at the boiling point of ethanal
• Collect ethanal as it is distilled off
Why is reflux used to oxidise a primary alcohol to a carboxylic acid?
Reflux doesn’t allow any reactant vapour to escape
Describe what happens when ethanol in the reaction mixture is refluxed and why it is necessary,
for complete oxidation to a carboxylic acid
Ethanol H2SO4 and acidified potassium dichromate(VI) are heated to boiling point for a prolonged time
• Ethanal vapour is formed which escapes from the liquid mixture and is then condensed back into liquid and returned to the reaction mixture
• Any ethanal and ethanol that initially evaporates can then be oxidised
In industry, this fermentation reaction is carried out at 35 °C rather than 25 °C.
Suggest oneadvantage and one disadvantage for industry ofcarrying out the
Fermentation at this higher temperature.
+: ethanol produced at a faster rate
-:more energy is needed by Thai reaction
Describe the different experimental conditions necessary to produce propanal
in high yield rather than propanoic acid (2)
Distillation
Immediately (the reagents are mixed)
Give one advantage and one disadvantage of manufacturing ethanol by
fermentation rather than by hydration.
Do not include energy consumption or cost.
+: low technology
renewable feedstock / resource
allowed for use in drinks, perfumes
considered to be green (1)
-:slow
low yield
significant land use
has to be distilled
labour intensive
In the production of bioethanol, glucose is converted into a dilute aqueous
solution of ethanol and carbon dioxide.
Give the name of this process and state three conditions necessary to
produce a yield of ethanol.
fermentation
M2 (enzymes from) yeast
M3 25°C ≤ T ≤ 42°C
M4 anaerobic / no oxygen
Explain why the ethanol produced by this process may not be a carbon-neutral
biofuel.
A specified process e.g. planting / harvesting / transport / extracting sugar /
distilling ethanol solution / fertiliser production etc.
M5 The specified process uses / burns (fossil) fuel that releases CO
Suggest one reason, other than safety, why this method is not used in industry to
make ethanol.
The yield is low / not a high yield
* The rate of reaction slow
