ORGANIC OCR A LEVEL CHEMISTRY YEAR 12
EXAM ACTUAL QUESTIONS AND CORRECT
ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
What is a structura/chain isomer?
-Same molecular formula but a different structural formula
What are the rules with structural isomers?
-Affect carbon chain length
-Alkyl side chain cannot be on the first carbon - the overall carbon chain length must remain the
same
-Cyclic alkanes are not structural isomers of alkanes (they a are structural isomers of alkenes)
What is the melting and boiling points of alkanes like?
-as chain length increases so does the strength of the intermolecular forces as there is greater
surface area for contact between molecules and hence stronger london forces and therefore the
melting/boiling points are highr for longer chain.
What are cycloalkanes?
alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure
general formula CnH2n
What is the combustion of an alkane?
-The reaction of the alkane with O2
-Exothermic
When does complete combustion take place?
-When there is excess oxygen available
What is the first stage of free radical substitution?
-Initiation
-This is where the free radicals are generated
-Cl2 -> Cl. + Cl.
,-U.V light causes the homolytic fission of the Cl-Cl covalent bond generating two Chlorine free
radicals
-A free radical is a highly reactive species with an unpaired electron
What is the second stage of free radical substitution?
-Propagation
-This is the alkane hydrogen atoms are substituted for the halogen free radical
-CH4 + Cl. -> .CH3 + HCl
-.CH3 + Cl2 -> CH3Cl + Cl.
-The first free radical generated is .CH3 which is a methyl free radical
-The Cl. Is regenerated and is what causes the chain reaction to take place as it reacts with more
CH4 producing more of the desired CH3Cl product
What is the third stage of free radical substitution?
-Termination
-This is where the free radicals combine to stop the chain reaction
-Cl. + Cl. -> Cl2
-Cl. + CH3. -> CH3Cl (desired product)
-CH3. + CH3. -> C2H6 (Ethane - alkane twice the size of the original alkane is produced)
What is the overall equation of free radical substitution?
-CH4 + Cl2 -> CH3Cl + HCl
What is the general formula of alkenes?
-CnH2n
-However, only with 1 C=C double bond as with more double bonds there will be less H atoms
What are the limitations of free radical substitution?
cannot occur in the dark
further substitution :if left to run multiple may occur and so not a very precise process
position in the chain : cannot control which h atom is substituted as is a random process so also
not precise
Are alkenes saturated or unsaturated and why?
-Unsaturated because they have a C=C double bond
, -This means they are open to addition reactions
Are alkenes polar or non-polar and how does this affect their water solubility?
-Non-polar
- c and h similar electronegativities and hence non-polar bonds and hence no dipoles so non-polar
molecule
-This means they are insoluble in water (water is polar)
Are alkenes reactive or unreactive?
-Very reactive
-The Pi bond of the C=C double contains two p-orbital overlaps which stick out above and below
the two nuclei of the bonding atoms
-The Pi bond is the bond that breaks during an addition reaction (as it is weaker)
-This makes the C=C double an area of high electron density and so it is open to electrophilic
attack
Describe the boiling points of alkenes
-Varied
-Their boiling point increases with increasing carbon chain length as their Mr increases
-This means that more electrons are involved in the formation of london dipersion forces
-Therefore there are stronger london dispersion forces which require more energy to overcome
What type of isomerism do alkenes show?
-sterioisomerism
-They have a non-rotational C=C double bond
Describe the alkene C=C double bond
-Functional group
-Area of high electron density
-Open to electrophilic attack
What are the products of complete combustion?
-CO2 and H2O
How do you balance alkane combustion equations?
EXAM ACTUAL QUESTIONS AND CORRECT
ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
What is a structura/chain isomer?
-Same molecular formula but a different structural formula
What are the rules with structural isomers?
-Affect carbon chain length
-Alkyl side chain cannot be on the first carbon - the overall carbon chain length must remain the
same
-Cyclic alkanes are not structural isomers of alkanes (they a are structural isomers of alkenes)
What is the melting and boiling points of alkanes like?
-as chain length increases so does the strength of the intermolecular forces as there is greater
surface area for contact between molecules and hence stronger london forces and therefore the
melting/boiling points are highr for longer chain.
What are cycloalkanes?
alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure
general formula CnH2n
What is the combustion of an alkane?
-The reaction of the alkane with O2
-Exothermic
When does complete combustion take place?
-When there is excess oxygen available
What is the first stage of free radical substitution?
-Initiation
-This is where the free radicals are generated
-Cl2 -> Cl. + Cl.
,-U.V light causes the homolytic fission of the Cl-Cl covalent bond generating two Chlorine free
radicals
-A free radical is a highly reactive species with an unpaired electron
What is the second stage of free radical substitution?
-Propagation
-This is the alkane hydrogen atoms are substituted for the halogen free radical
-CH4 + Cl. -> .CH3 + HCl
-.CH3 + Cl2 -> CH3Cl + Cl.
-The first free radical generated is .CH3 which is a methyl free radical
-The Cl. Is regenerated and is what causes the chain reaction to take place as it reacts with more
CH4 producing more of the desired CH3Cl product
What is the third stage of free radical substitution?
-Termination
-This is where the free radicals combine to stop the chain reaction
-Cl. + Cl. -> Cl2
-Cl. + CH3. -> CH3Cl (desired product)
-CH3. + CH3. -> C2H6 (Ethane - alkane twice the size of the original alkane is produced)
What is the overall equation of free radical substitution?
-CH4 + Cl2 -> CH3Cl + HCl
What is the general formula of alkenes?
-CnH2n
-However, only with 1 C=C double bond as with more double bonds there will be less H atoms
What are the limitations of free radical substitution?
cannot occur in the dark
further substitution :if left to run multiple may occur and so not a very precise process
position in the chain : cannot control which h atom is substituted as is a random process so also
not precise
Are alkenes saturated or unsaturated and why?
-Unsaturated because they have a C=C double bond
, -This means they are open to addition reactions
Are alkenes polar or non-polar and how does this affect their water solubility?
-Non-polar
- c and h similar electronegativities and hence non-polar bonds and hence no dipoles so non-polar
molecule
-This means they are insoluble in water (water is polar)
Are alkenes reactive or unreactive?
-Very reactive
-The Pi bond of the C=C double contains two p-orbital overlaps which stick out above and below
the two nuclei of the bonding atoms
-The Pi bond is the bond that breaks during an addition reaction (as it is weaker)
-This makes the C=C double an area of high electron density and so it is open to electrophilic
attack
Describe the boiling points of alkenes
-Varied
-Their boiling point increases with increasing carbon chain length as their Mr increases
-This means that more electrons are involved in the formation of london dipersion forces
-Therefore there are stronger london dispersion forces which require more energy to overcome
What type of isomerism do alkenes show?
-sterioisomerism
-They have a non-rotational C=C double bond
Describe the alkene C=C double bond
-Functional group
-Area of high electron density
-Open to electrophilic attack
What are the products of complete combustion?
-CO2 and H2O
How do you balance alkane combustion equations?
