Organic Reactions SL

Question 1

Addition reactions

Answer 1

occurs when two reactants combine to form a single product
characteristic of unsaturated compounds

Question 2

Substitution reactions

Answer 2

occurs when one atom or group of atoms in a compound is replaced by a different atom or group
characteristic of saturated compound and aromatic compounds

Question 3

Addition/elimination

Answer 3

occurs when two reactants join together and in the process small molecule is lost
reaction occurs between a functional group in each reactant
also called a condensation reaction

Question 4

Homolytic fission

Answer 4

when a covalent bond breaks by splitting the shared pair of electrons between the two products
produces two free radicals, each with an unpaired electron

Question 5

Heterolytic fission

Answer 5

is when a covalent bond breaks with both the shared electrons going to one products
produces two oppositely charged ions

Question 6

Combustion reactions of the alkanes

Answer 6

when alkanes burn
the products of combustion depend on the amount of oxygen available

Question 7

Free radical substitution of alkanes

Answer 7

also called halogenation
as alkanes are saturated
a halogen takes the place of a hydrogen atom in the alkane
1. initiation
presence of UV light
known as photochemical homolytic fission
Cl2 -> Cl. + Cl.
2. propagation
used and produces free radicals
there are many possible propagation steps which all allow for the reaction to continue
often called chain reactions
Cl. + CH4 -> CH3. + HCl
CH3. + Cl2 -> CH3Cl + Cl.
CH3Cl + Cl. -> CH2Cl. HCl
3. termination
removes free radicals by causing them to react together and pair up their electrons
Cl. + Cl. -> Cl2
CH3. + Cl. -> CH3Cl
CH3. + CH3. -> C2H6

Question 8

Alkene reaction with hydrogen

Answer 8

called hydrogenation
alkene + Ni catalyst -> alkane

Question 9

Alkene reaction with chlorine

Answer 9

alkene + chlorine + Ni catalyst -> dihaloalkane

Question 10

Reactions with bromine

Answer 10

is the standard test fo the presence of a double or triple bond between carbon atoms
a solution of bromine changes from orange to colourless if the molecule is unsaturated

Question 11

Alkene reaction with hydrogen halides

Answer 11

alkene + HX (X = halogen) -> haloalkane

Question 12

Alkene + water

Answer 12

known as hydration
converts the alkene to alcohol
achieved using concentrated sulfuric acid as a catalyst and heat

Question 13

Addition polymerisation of alkenes

Answer 13

polymers are formed when small molecules (monomers) bond together to give long chains of carbon atoms and very high molar masses

Question 14

Classification of alcohols

Answer 14

primary - the OH is attached to 1 R group (end of carbon chain)
secondary - it is attached to 2 R groups (at a branch of carbon chain)
tertiary - attached to 3 R groups

Question 15

Combustion of alcohols

Answer 15

form carbon dioxide and water
amount of energy released per mole of alcohol increases as we go up the homologous series
in limited supply of O it forms CO and H2O

Question 16

Oxidation of primary alcohols

Answer 16

oxidised by acidified potassium permanganate and acidified potassium dichromate
when oxidised potassium permanganate changes from purple to colourless and potassium dichromate changes from orange to green
primary alcohol + heat -> aldehydes + heat -> carboxylic acid
the carboxylic acid and aldehyde are obtained through different methods
- to isolate aldehyde, heat up the solution and distil out the vapour as fast as it is formed
-to obtain the carboxylic acid heat and reflux, attach a condensing tube to your flask so that vapors condense before they escape

Question 17

Oxidation of secondary alcohols

Answer 17

oxidised by acidified potassium permanganate and acidified potassium dichromate
when oxidised potassium permanganate changes from purple to colourless and potassium dichromate changes from orange to green
secondary alcohol + heat -> ketones

Question 18

Oxidation of tertiary alcohols

Answer 18

this reaction can not occur

Question 19

Esterification

Answer 19

alcohols react with carboxylic acids to form esters in a condensation reaction with concentrated sulfuric acid as a catalyst and heat
carboxylic acid + alcohol -> ester + water

Question 20

Nucleophilic substitution reactions of halegenoalkanes

Answer 20

the polarity in halegenoalkanes is due to the fact that the halogen atom is more electronegative than carbon
therefore it is said to be electron deficient and so are attracted to nucleophiles (electron rich species)
discussed more later

Question 21

electrophilic substitution reactions of benzene

Answer 21

delocalised electrons in benzene give it special stability
addition reactions are not favorable so substitution reactions occur where one or more of the hydrogen atoms is replaced by an incoming group
the arene ring is conserved
electrophiles are attracted to the electron rich benzene ring