Module 4 Flashcards
Define homologous series
A series of organic compounds having the same functional group but with each successive member differeing by CH2
Define structural isomers
Compounds with the same molecular formula but different structural formulae
Define homolytic covalent bond fission
Each bonding atom receiving one electron from the boned pair, forming two radicals
Define heterolytic covalent bond fission
One bonding atom receiving both electrons from the bonded pair
Define radical
A species with an unpaired electron, and is represented by a dot: •
Explain the use of a ‘curly arrow’ in mechanisms
It shows the movement of an electron pair, showing either heterolytic fission, or formation of a covalent bond
Define alkanes
Saturated hydrocarbons containing single C-C and C-H bonds as σ-bonds.
What is a σ-bond?
Overlap of orbitals directly between the bonding atom, so have free rotation of the σ-bond
Describe and explain the shape and bond angles in alkanes
Alkanes are formed up of four atoms bonded to a central atom, so they repel equally giving a tetrahedral shape and a bond angle of 109.5°
Describe the difference in boiling points of alkanes
- Increasing the chain of a alkane increases the amount of london forces, meaning more induced dipoles can occur, so an increase in boiling point
- Increasing the amount of branching decreases the surface area of contact between molecules, giving fewer London forces, so less induced dipoles, so a lower boiling point
Explain the low reactivity with alkanes with many different reagents
Alkanes have very high bond enthalpies and very low polarity of the σ-bonds present, so is very unreactive
Describe the combustion of alkanes
- Alkanes combust in excess oxygen to form carbon dioxide and water
- This is why they can make good fuels
- Alkanes combust in limited oxygen to form carbon monoxide (or carbon) and water
- This can cause potential dangers as CO prevents oxygen from binding to haemoglobin.
Name the type of reaction between a alkane and a halogen (Either chlorine or bromine)
Radical substitution
Describe the mechanism for the bromonation of methane
- Initiation
- Br2 → 2Br• (Under UV radiation)
- Propagation
- CH4 + Br• → •CH3 + HBr
- •CH3 + Br2 → CH3Br + Br•
- Termination (either of them could have)
- 2Br• → Br2
- 2•CH3 → C2H6
- •CH3 + Br• → CH3Br
Explain the limitations of using radical substitution in organic synthesis
- Further substitution can occur
- Can react at different positions in a carbon chain, so large mixture of products are formed
Define alkenes
Unsaturated hydrocarbons containing a C=C bond comprising a π-bond and a σ-bond, giving restricted rotation around the C=C bond
What is a π-bond?
Sideways overlap of adjacent p-orbitals above and below the bonding atoms
Explain the shape and bond angle of alkenes around the carbons which are part of the C=C
There are three bonded atoms to the central carbon atom, and they all equally repel, giving a trigonal planer shape and a bond angle of 120°
Define stereoisomers
Compounds with the same structural formula, but with a different arrangement in space
Define E/Z isomerism
An example of stereoisomerism where restricted rotation about a double bond and the requirement of two different groups to be attached to each carbon atom of the C=C group
Define cis-trans isomerism
A special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom of the group is the same
Explain how the Cahn-Ingold-Prelog (CIP) priority rules are used to identify the E and Z stereoisomers
- Groups of higher priority on the same side have Z isomerism
- Groups of higher priority on the opposite side have E isomerism
- Priority is given the atom attached directly to the carbon atom of the double bond with the highest atomic number
- If the atom directly attached is the same, then the next atom is looked at, until one with a higher priority (even if it is nothing compared to an atom) is found
Why are alkenes more reactive than alkanes?
For alkenes have the unsaturated C=C bond which has a low bond enthalpy
Define electrophile
An electron pair acceptor
State the reagents and conditions for the hydrogenation of alkenes
Hot hydrogen is bubbled through the alkene over a nickel catalyst
State the reagents and conditions for the halogenation of alkenes
Either a halogen or a hydrogen halide, and no special conditions required
State the reagents and conditions for the hydration of alkenes
Steam and an acid catalyst, e.g. H3PO4, to form an alcohol
Draw the mechanism for the electrophilic addition reaction of an alkene with hydrogen bromide
Draw the mechanism for the electrophilic addition reaction of an alkene with bromine
Explain with the use of Markownifkoff’s law how you can tell which is the most likely product formed in addition reactions
The intermidate most likely to form is the one with the most stable carbocation, with tertiary being the most stable, and primary being least stable.
Describe how to determine the repeat unit of an addition polymer from the monomer
The C=C bond opens out, with the other groups above and below the carbon, even if just part of the carbon chain
Descibe how to determine the monomer which would produce a given section of an addition polymer
Whenever the polymer repeated, often every to carbons along the addition polymer
Discuses the benefits for sustainability of processing waste polymers
Compare the water solubility and volatility of alcohols to alkanes
- Alcohols form hydrogen bonds with water, allowing them to interact, whilst alkanes are non-polar, so don’t dissolve
- Alcohols form hydrogen bonds with each other, giving them strong intermolecular forces, whilst alkanes only have London forces, making them more volatile
Describe how to classify alcohols as primary, secondary and tertiary
The number of R groups attached to the carbon which has the -OH functional group attached to it
Describe the combustion of alcohols
They burn completely in a plentiful supply of oxygen, as like alkanes and alkenes, and the heat released per mole increases as the chain increases
Describe the oxidation of a primary alcohol
Under distiliation with acidified potassium dichromate(VI):
RCH2OH + [O] → RCOH + H2O
Under reflux:
RCH2OH + 2[O] → RCOOh + H2O
Describe the oxidation of secondary alcohols
Under reflux and with acidified potassium dichromate(VI):
RCH2OHR + [O] → RCOR +H2O
Describe the oxidation of a tertiary alcohol
Tertiary alcohols resist oxidation, so do not oxidise readily
Describe the dehydration of alcohols
The alcohol has a water molecule eleminated from it, in the presence of an acid catalyst, leaving an alkene and water as the products
Describe the halogenation of alcohols
- A metal halide and acid are mixed and heated under reflux together to create the hydrogen halide ‘in situ’.
- The halogen substitutes the alcohol group, in a nucleophilic substitution reaction.
Define nucleophile
An electron pair donor
State and explain the reagents and conditions for the hydrolysis of a haloalkane by aqueous alkali
- The OH group from the aqueous alkali (e.g. NaOH) replaces the halogen atom
- The reaction is heated under reflux to increase the rate of reaction
Explain how the repulsion between the halogen’s dipole and charge on the OH is minimised
The OH nucleophile approaches the carbon atom from the opposite side of the molecule with the halogen
Describe an experiment to compare the rates of hydrolysis of haloalkanes
- Mix the haloalkanes with water and AgNO3 and place in a water bath
- Time how long it roughly takes for each precipitate (of the silver halide) to form
- The quicker the precipitate formed, the weaker the bond enthalpy between the carbon and halogen atom
State and explain the trend in the rates of hydrolysis of primary haloakanes
- Iodoalkanes have the fastest rate, and chloroalkanes have the slowest
- This is caused by C-Cl having the highest bond enthalpy due to it having the strongest dipole
- C-F has such a high bond enthalpy, so are unreactive, as a large quantity of energy is required to break that bond
Show the mechanism for the nucleophilic substitution in the hydrolysis of primary haloalkanes with aqueous alkali
Describe the production of halogen radicals in the upper atmosphere
Compounds like CFC’s split due to UV radiation and form a halogen radical, e.g. •Cl
Show the propagation of the catalysed breakdown of ozone by a radical
E.g.
•NO + O3 → NO2• + O2
NO2• + O → NO• + O2
Overall:
O3 + O → 2O2
Describe the difference between heating under reflux and distillation
When heating under reflux, the condenser is upright, causing any heated reactants to condense back down into the flask
When heating under distillation, the condenser is placed parallel to the surface (at a slight angle still though), allowing the product to evaporate off and then condense in the condenser and be collected separately
Describe the preparation and purification of an organic solid
- Purify the organic produc by using a separating funnel
- Dry with an appropriate anhydrous salt
- Redistil
Describe how to use a separating funnel
- Ensure the tap is closed and pour the mixture into the funnel
- Invert to mix, and then allow to settle
- Add a small amount of distilled water, and the layer which increases is the aqueous layer
- Place a flask under the funnel and run off the lower layer
- Swap the flask under the funnel and run off the other layer
- Label the flasks, so not to get them mixed up
Describe how to dry and organic liquid
- Add the liquid to a conical flask
- Using a spatula, add an appropiate drying agent to the liquid and gently swirl. Insert a stopper to stop evaporation, and then wait for 10 minutes
- If the solid sticks together in a lump, there is still water present, so add more drying agent until it is dispersed in the solution as a fine powder
- Decant the liquid from the solid into another flask, and should be clear if dry
