4.1 basic concepts and hydrocarbons

Question 1

general formula

Answer 1

Simplest algebraic formula of a member of a homologous series
Alkanes- CnH2n+2 Alkenes- CnH2n

Question 2

homologous series

Answer 2

Series of organic compounds having the same functional group but with each successive member different by CH2

Question 3

functional group

Answer 3

Group of atoms responsible for the characteristic reactions of a
compound
E.g.- -Cl, -OH

Question 4

functional group isomerism

Answer 4

Position of atoms cause a different functional group

Question 5

structural isomerism

Answer 5

Compounds with the same molecular formula but a different structural formula

Question 6

chain isomerism

Answer 6

Isomers have different chain length caused by branching

Question 7

positional isomerism

Answer 7

The position of a functional group differs along a chain

Question 8

isomerism

Answer 8

Aliphatic isomers –
compound arranged in a non-aromatic rings. With or without branching chains
Aromatic isomers-
a compound containing a benzene ring
Structural isomers- Compounds with the same molecular formula but a different structural formula

Question 9

saturated

Answer 9

single carbon–carbon bonds only) and unsaturated (the presence of multiple carbon–carbon bonds, including C=C, C multiple / and aromatc rings

Question 10

saturated

Answer 10

single carbon–carbon bonds only) and unsaturated (the presence of multiple carbon–carbon bonds, including C=C, C multiple / and aromatc rings

Question 11

covalent bond fission- homolytic

Answer 11

in terms of each bonding atom receiving one electron from the bonded pair, forming two radicals

Question 12

covalent bond fission- heterolytic fission

Answer 12

in terms of one bonding atom receiving both electrons from the bonded pair

Question 13

radicals

Answer 13

a species with an unpaired electron
‘dots’ represent species that are radicals in mechanisms
Dots, •, are required in all instances where there is a single unpaired electron (e.g. Cl• and CH3•).
Dots are not required for species that are diradicals (e.g. O). (h)

Question 14

curly arrow

Answer 14

Is described as the movement of an electron pair, showing either heterolytic fission or formation of a covalent bond

Question 15

alkanes

Answer 15

saturated hydrocarbons containing single C–C and C–H bonds as σ-bonds (overlap of orbitals directly between the bonding atoms) which allow free rotation of the σ-bond
Is non-polar, so has only London dispersion forces
Is only soluble in non-polar solvents.
The properties depend on chain length and branching
More points of contact mean there are more intermolecular forces

Question 16

boiling point of alkanes

Answer 16

Increases with the length of chain
Packing describes how closely they can get together and branching in alkanes cause them to not pack as close together, which lowers the boiling point

Question 17

alkanes and reactivity

Answer 17

Low because of:
Low polarity
High bond enthalpy
A very slight dipole but still non-polar

Question 18

combustion of alkanes

Answer 18

Is exothermic- addition of oxygen 
Complete when there is excess oxygen 
CH4 + 2O2 → CO2 + 2H2O 
Incomplete when there is limited oxygen 
CH4 + O2 → C + 2H2O
CH4 + 2O2 → CO + 2H2O
Complete calculations are often balanced so that the fuel is given as 1 mol, allowing oxygen to have halves

Question 19

oxidation of alkanes

Answer 19

Combustion of methane 
CH4 + 1 ½ O2 → CO + 2H2O
CH4 + O2 → C + 2H2O
CH4 + 2O2 → CO2 + 2H2O
Carbon is reduced and hydrogen is oxidised

Question 20

radical substitution

Answer 20

An unbonded electron in an atom/molecule is highly reactive
Formed by homolytic fission ( homolysis)
Homolytic- each atom in a bond takes 1 of the shared electron
Fission- splitting of the covalent bond .
UV radiation has enough energy to split a covalent bond within bonds to form radicals.
∙ represents an unpaired electron

Question 21

what are the 3 stages to radical substitution

Answer 21

Initiation- radical formation
Propagation- formation of product and new radicals
Termination- reaction ends as radical is removed

Question 22

alkenes

Answer 22

unsaturated hydrocarbons containing a C=C bond comprising a π-bond (sideways overlap of adjacent p-orbitals above and below the bonding C atoms) and a σ-bond (overlap of orbitals directly between the bonding atoms)

Question 23

stereoisomerism

Answer 23

Occurs in compounds with the same structural formula but different arrangement in space
The pi- bond in alkenes restrict the rotation of the molecule potentially causing E/Z isomerism
Sigma-bonds can rotate so stereoisomerism cant occur in alkanes

Question 24

E/Z stereoisomerism

Answer 24

Can only occur if:
There’s a C=C bond
Each carbon is bonded to a different atom/group
E-isomerism- priority groups are on opposite sides
Z-isomerism- priority groups are on the same side

Question 25

Cahn, Ingold and Prelog

Answer 25

assign stereoisomers as either E or Z, using the atomic number of the atom that is directly bonded to C=C
The rules:
- Highest atomic numbers are diagonally opposite
- Highest atomic numbers aren’t diagonally opposite ( Z- isomers)
- Is atomic numbers are equal, the adjacent atoms are taken into account.
- Longer alkyl chains take priority

Question 26

cis/trans isomerism

Answer 26

A type of E/Z isomers where 2 of the substituent groups on the C=C bond are the same.
Cis- not diagonally opposite
Trans- diagonally opposite

Question 27

electrophile

Answer 27

an electron pair acceptor so there are often positive ions or have a 𝛿+ dipole

Question 28

alkene reactions

Answer 28

The lower bond enthalpy of a pi-bond compared to a sigma-bond makes alkenes more reactive than alkanes
The position of the pi-bond above and below the molecule also makes it easier to ‘attack’ the electron pair
All alkenes undergo addition reactions whereby 2 reactants combine to form a single product
With species bonding either side of the
C=C bond

Question 29

Markownikoff’s rule

Answer 29

When an asymmetrical alkene reacts with a hydrogen halide or water molecule, there are 2 possible isomers formed
But 1 isomer is more commonly produced than the other.
States that the hydrogen being added bonds to the carbon with the most hydrogen present

Question 30

addition polymerisation

Answer 30

Alkenes can undergo addition reactions in which 1 alkene molecule ( a monomer) joins to another until a long molecular chain is built up ( a polymer).
Polymerisation can be initiated in a number of ways.
Often, the initiator is incorporated at the start of the long molecular chain.
However, if the imitator is disregarded, the empirical formulae of the monomer and polymer is the same

Question 31

problems with polymers

Answer 31

The problem with addition polymers is that they don’t biodegrade ( rot)
They persist in the environment and this can cause problems such as turtles eating plastic bags thinking they are jellyfish

Question 32

photo-degradation

Answer 32

They break down into smaller fragments as a result of sunlight but each fragment is the same addition polymer and this can cause different problems, such as ingestion by filter-feeding organisms

Question 33

recycling

Answer 33

Usually means melting down and re-forming into new products
Is expensive because there are many different polymers in domestic waste and they must be separated by hand before melting.
This leads to contamination- so recycled polymers are always lower quality than freshly manufactured ones.
Some polymers are thermoset- don’t melt when heated ( although they could still burn.)

Question 34

chemical-feedstock recycling

Answer 34

Breaks down polymers without separating them, forming simple gases that can then be used to manufacture pure, fresh polymers.
This system is yet to be shown to work.

Question 35

incineration

Answer 35

Burning them removes the polymers and can generate power as an additional benefit- thereby saving fossil fuels.
Is a worry about toxic products of some polymers and those polymers can contain chlorine ( such as PVC) would create HCl as a waste gas.
Adds expense as it would be necessary to neutralise the waste gases to avoid acid rain.