1.
Define Alkanes: i) Only C-C bonds
ii) All sp³ C atoms
iii) Non-polar, insoluble in water&polar solvents
iv) Soluble in non-polar organic solvents (e.g. CCl4, benzene)
v) Less dense than water, forms an upper layer above water layer
vi) Inter-molecular Van der Waals forces. Stronger VDW, higher melting points/boiling points, *dependent on no. of electrons and surface area of molecule
1. Unreactive with polar solvents
2. Combustion
3. Substitution by halogen
2.
Describe Alkenes: i) Unsaturated
ii) C=C
iii) Cannot be rotated because the pi bond would break, can form cis-trans isomers
iv) Also has VDW forces affected by number of electrons and surface area
1) Combustion
2) Addition of hydrogen
3) Addition of Steam
4) Addition of H-X via ELECTROPHILIC ADDITION
5) Addition of halogen
6) Oxidation by cold, dilute alkaline manganate(VII) ions [test] - produce brown MnO2 + decolorization of purple KMnO4
7) Oxidation by hot, concentrated acidified manganate(VII) ions [test]
3.
Describe free radical substitution: Initiation: Proton of light breaks up chlorine molecule into 2 chlorine atoms/radicals
Propagation:
Radicals react with ethane to give ethyl radical + HCl
Ethyl radical can react with Cl-Cl to form more Cl radicals
Termination:
Radicals are removed by homolytic fusion with another radical
4.
Describe the unreactivity of alkanes towards polar solvents: i) All the electrons and orbitals are used in bonding, thus no empty orbitals to form dative bonds with molecules
ii) Electronegativities of carbon and hydrogen are similar, thus C-H bond is only very slightly polarized. Also Carbon is more electronegative than the hydrogen, so the carbon is slightly negative in the C-H bond and will repel the negative oxygen in H2O and OH-
5.
Explain Substitution of Alkanes with halogen: Reacts with Halogen, in the presence of sunlight through free radical substitution reaction
Free radical: A particle in which 1 atom has an unpaired electron, formed by homolytic fission
6.
How to make Alkenes?: i) Cracking through strong heating
ii) Dehydration of alcohol (eliminate H-OH)
iii) Dehydrohalogenation (eliminate H-X)
7.
What are arenes?: Hydrocarbons with at least a benzene ring
i) reacts with B2 in presence of iron
ii) No Addition but with Substitution (delocalized ring of electrons)
iii) Note diagram for Substitution reaction
iV) Alkylation of Benzene
v) Nitration of Benzene
vi) Bromination
vii) Chlorination
viii) Hydrogenation (FYI)
8.
What are the pointers to note for Electrophilic Substitution?: 2-Directing
- Electron Donating substituents -OR, -OH, -NH2, -R
3-Directing
- Electron-withdrawing Substituents -COOH, -CRO, -CHO, -NO2, -COCl
*Halogen substituents are electron-withdrawing but they are 2 and 4 directing
4-Directing
- Electron Donating Substituents -OR, -OH, -NH2, -R
9.
What are the reactions of methylbenzene?: i) Substitution
ii) Halogenation of side chain
iii) Oxidation of side chain into aldehyde/ -COOH
