10.2

Question 1

reactions of alkanes

Answer 1

❏ Combustion with O2 → complete forms CO2 and H2O, incomplete also
forms CO and C
❏ Substitution with halogens in presence of UV light to form haloalkane
❏ Mechanism of the chlorination of methane (free radical
substitution), homolytic fission = each atom retains an electron
forming 2 free radicals (reactive, unpaired electrons)
❏ Initiation = produce Cl free radical
❏ Propagation = free radical on each side
❏ Termination = 3 ways to get rid of free radicals

Question 2

Reactions of Alkenes

Answer 2

❏ Hydrogenation with Ni(s) catalyst and 150oC → add hydrogen to
saturate
❏ Halogenation to produce dihalogeno cmpds by adding halogen (quickly
at SATP, no UV radiation, loss of colour of reacting halogen)
❏ Addition of hydrogen halides to produce halogenoalkanes, HI>HBr>HCl
(quickly in soln at SATP)
❏ Hydration reactions with concentrated H2SO4 catalyst in presence of H2O as steam → adding
water to produce alcohols (ethanol is an important industrial
solvent)
❏ Polymerization → produce addition polymers (addition
reactions with itself), monomer to polymer

Question 3

Reactions of Alcohols

Answer 3

❏ Combustion to produce CO2 and H2O (complete), longer
hydrocarbon chain = more energy released
❏ Oxidation with acidified solution of potassium dichromate(VI) and heat with distillation or reflux,
orange to green from Cr(VI) to Cr(III), write +[O] or H+/Cr(VIO, heat above arrow, oxidizing
agents selectively oxidize C atom attached to the -OH group, distillation/reflux = boiling processes
❏ Primary alcohol → (distillation) aldehyde → (reflux) carboxylic acid
❏ Secondary alcohol → (reflux) ketone
❏ Tertiary alcohol → no reaction
❏ Esterification with concentrated H2SO4 react carboxylic acid + alcohol to produce ester + water
(type of nucleophilic substitution), methanoic acid + ethanol → ethyl methanoate + H2O

Question 4

Reactions of Halogenoalkanes

Answer 4

❏ Nucleophilic substitution → substitute a nucleophile (loves
+ve), e- rich species that is attracted to e- deficient parts of a
molecule, halogenalkanes react with alkalis to from alcohol
and a salt, ex. chloromethane + NaOH → methanol + NaCl

Question 5

Reactions of Benzenes

Answer 5

❏ Electrophilic substitution → substitute an electrophile (loves
-ve) such as NO2+, H+, to protect stability of arene ring
❏ With concentrated H2SO4, 50oC for nitric acid HNO3 (subs in NO2, remainder as H2O)
❏ With AlCl3 in dry ether for Cl2 (subs in Cl+ and remainder as HCl)

Question 6

A free radical contains an unpaired electron and so is

Answer 6

very reactive.

Question 7

Homolytic fission occurs when

Answer 7

a bond breaks by splitting the shared pair of electrons between the two products. It produces two free radicals, each with an unpaired electron.
X : X → X* +

Question 8

Alkanes are

Answer 8

saturated hydrocarbons and undergo substitution reactions.

Question 9

Alkenes are

Answer 9

unsaturated hydrocarbons and undergo addition reactions.

Question 10

A nucleophile is

Answer 10

an electron-rich species that is attracted to parts of molecules that are electron deficient.

Question 11

An electrophile is

Answer 11

an electron-deficient species that forms a bond by accepting
an electron pair. electrophiles are positive ions or have a partial positive charge.