Alkanes

Question 1

How to name alkanes

Answer 1

1. identify parent chain grp (longest chain)
2. identify substitutents
3. position of substitutents arrangement based on alphabetical order

Question 2

Solubility of alkanes

Answer 2

Alkanes are non-polar molecules and are insoluble because the pd-id interactions formed between polar water molecules and alkanes do not release enough E to overcome strong H bonds of water

Question 3

Talk abt the BP of alkanes

Answer 3

The higher the number of carbon atoms, the higher the BP as with increased number of electrons, the id-id interactions become stronger hence more E required to overcome

Question 4

Talk abt MP of alkanes

Answer 4

zig-zag pattern as imf dependent on size of molecule and how packed they are

Question 5

Explain how to form alkanes

Answer 5

Reagents H2 gas
conditions Ni catalyst with heat or pt/pd at rtp
alkene—> alkane

Question 6

Talk about initiation

Answer 6

Under high temp, heat or UV light. The halogen undergoes homolytic cleavage of Cl-Cl bonds to generate Cl. free radicals. show half arrow in reaction

Question 7

Talk about propogation

Answer 7

During propagation, a cl radical is consumed in one step and generated in another.
e.g. CH3CH3 + Cl –> CH3CH2
CH3CH2 + Cl2 –> CH3CHCl + Cl

Question 8

Talk about termination

Answer 8

Free radicals are consumed but no generated

Question 9

Explain the reactivity of halogens

Answer 9

When the size of the halogen atom increases down the group, there is a less effective overlap of orbitals which causes the C-X and H-X bonds to get weaker. Since delta H becomes more exo, it is easier to sub

Question 10

How to calculate the expected yield of smth. Why are there discrepancies

Answer 10

Look at how many positions around atoms can be formed. There are discrepancies because the secondary and tertiary alkyl groups are more stable and formed preferentially. This is because alkyl groups exert electron donating inductive effect which stabilises carbon radical by increasing electron density on electron deficient C atom

Question 11

Why are alkanes generally unreactive

Answer 11

Due to their similar electronegativities, the alkanes are non-polar and lack electron rich or deficient areas for polar molecules and ions to attack. or C-C and C-H bonds are very hard to overcome so they require alot of energy to overcome