2.4 Hydrocarbons Flashcards
What is a hydrocarbon?
A compound of hydrogen and carbon only
What is a homologous series?
A family of compounds with the same functional group
What is a functional group?
Group of atoms responsible for properties
Define a structural isomer
Same molecular formula but different structural formula
Define a positional isomer
Same molecular formula but different arrangement of functional group
Name the chains 1-10
- methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane
What are the different types of organic formula?
- structural: say it as you see it is CH3CH2CH2OH
- display: draw out every bond
- molecular: simplest collation of each element
- empirical: simplest whole number ratio
- skeletal: backbone where hydrogens are assumed and functional groups bolted
Define aliphatic and aromatic
- aliphatic: straight chain
- aromatic: cyclic structures
What are the naming rules?
- Longest C chain for parent
- Identify parent functional group
- Organise functional groups alphabetically
- Number position of function groups, lowest possible
- Dashes between letters and numbers, commas between numbers
- Piece it all together
Alkane functional group
- ane
- C-C
- CnH2n+2
Alkene functional group
- ene
- double bond C
- CnH2n
Halogenoalkanes functional group
- fluoro/chloro/bromo/iodo-
- R-X (attached to C anywhere in chain)
- CnH2n+1X
Alcohols functional group
- ol
- R-OH
- CnH2n+1OH
Aldehyde functional group
- al
- R-C double bond O top, H bottom
- R-CHO
Ketone functional group
- one
- double bond O anywhere in chain
- R-CO-R
Carboxylic acid functional group
- oic acid
- R-C double bond O on top, OH bottom
- R-COOH
Would a straight carbon chain or cross linked carbon chain have the highest boiling point?
- straight chain isomers have more points of contact than cross linked so more VdW interaction and therefore more energy to break
Reactions of alkanes
- very unreactive as saturated
- radical substitution
Define a radical
A species with an unpaired electron
Explain the stages of radical substitution
Initiation: UV rays break molecules apart by homolytic bind fission. 1 electron to each atom to make 2 independent radicals
Propagation: reaction with radical and starting molecule
Termination: process ends when radical reacts with radical
Explain the bonding in alkenes
- carbon double bond made of one sigma bind and one pi bond
- caused by P-orbitals overlapping resulting in areas of high electron density known as a pi cloud
How can you make alkenes?
- heat with platinum or do elimination reaction
- catalytic cracking ( useless long chain hydrocarbons made into shorter more useful ones )
Define an electrophile
An electron loving species with a positive charge
Define a nucleophile
A nuclei loving species with a -ve charge
How do you test for alkenes?
- add bromine
- decolourises
Outline electrophilic addition for C2H4 and Br2
Explain isomerism in alkenes
- 2 stereoisomers are formed - same structural formula but different arrangement of atoms in space
- 2 conditions needed: C=C, two diff groups of atoms on each carbon
How to make alcohols with alkenes
- add H20, steam form
- 60atm, 300°C, H3PO4 catalyst
How to make alkanes from alkenes
- add H2
- 150°C, nickel/platinum catalyst
Explain why ethanol is soluble in water but ethanol is not
Ethanol can form hydrogen bonds with water molecules whereas ethane cannot
Explain E and Z isomers
E: opposite
Z: same
Describe bonding in alkenes and use this to explain its reactivity
- C=C double bond of one sigma and one pi
- sigma made by overlap of s orbitals, pi by overlap of p orbitals that creates areas of high electron density known as pi cloud
- makes them susceptible to electrophilic attack leading to addition reactions
What feature of a molecule gives rise to EZ isomerism
C=C bond
Reagents for elimination reaction
- NaOH in ethanol
- heat
How to distinguish between cyclohexane and hexene
- add bromine water
- hexene decolourises bromine water but cyclohexane does not
Additional reagents to test for alkenes
Potassium manganate
