C12 - alkanes

Question 1

free radical substitution steps

Answer 1

1) Initiation
UV light causes homolytic fission, and produces free radicals
2) Propagation
free radical + molecule form a different free radical and a different molecule
3) termination
All free radicals produces react together
usually 3 possible products

Question 2

What are alkanes?

Answer 2

• main components of crude oil
• most stable organic compounds
• mainly used as fuels (react with O2 and generate heat)

Question 3

complete combustion of alkanes

Answer 3

alkane reacts with excess oxygen and burns completely to form CO2 and H2O

Question 4

incomplete combustion of alkanes

Answer 4

limited oxygen supply
toxic gas carbon monoxide (CO) or soot (Just C) formed

Question 5

are alkanes or alkenes more reactive? Why?

Answer 5

alkenes more reactive

unreactive sigma bond in alkanes (allows crude oil deposits to remain in the earth)

pi bond in alkanes more reactive

Question 6

Structural isomers have different boiling points. Why do branched isomers have a lower boiling point?

Answer 6

• molecules further apart sue to branching
• less surface contact
• less/weaker London forces
• lower boiling point

Question 7

what is a sigma bond?

Answer 7

a single covalent bond

Question 8

Why is a sigma bond so unreactive?

Answer 8

C-C non polar

C-H have similar electronegativity so
also non-polar

v. strong sigma bonds

Question 9

limitations of free radical substitution

Answer 9

1) further substitution:
more free radicals could collide with products
2) substitution at different positions on the carbon chain:
for longer carbon chains there will be a mixture of monosubstituted isomers
e.g. bromine could bind to 3 different positions on pentane

Question 10

fractional distillation

Answer 10

can separate crude oil components with different boiling points