topic 6: organic 1 mechanisms

Question 1

radical

Answer 1

species with an unpaired electron

Question 2

2 limitations of free radical substitution

Answer 2

• over substitution
• forms a mixture of products

Question 3

oversubstitution

Answer 3

the hydrogens can KEEP getting replaced by chlorine atoms

Question 3

initiation

Answer 3

diatomic molecule forms 2 radicals via homolytic fission using UV light

Question 3

how is a radical formed

Answer 3

homolytic fission of a covalent bond

Question 3

homolytic fission

Answer 3

bond splits evenly; each atom gets 1 of the 2 electrons in a covalent bond

Question 4

propagation

Answer 4

1 radical x 1 non-radical react

Question 5

termination

Answer 5

2 radical react to form a non-radical

Question 5

reagent in FSR

Answer 5

halide

Question 6

condition in FSR

Answer 6

UV

Question 7

how to ensure full over substitution (tetrahaloalkane)

Answer 7

add excess halogen

Question 8

definition of electrophilic addition

Answer 8

addition of an electrophile to a double bond

Question 9

alkene + hydrogen

Answer 9

HYDROGENATION
- nickel catalyst
- alkane formed

Question 10

manufacture of margarine

Answer 10

• uses hydrogenation
• naturally occurring veg oils are unsaturated (c=c)
• converts into a solid margarine

Question 11

oxidising agent

Answer 11

acidified poatssium mangante
(KMnO4)

Question 12

alkene + KMnO4

Answer 12

• oxidisation
• pale purple goes colourless. diol product formed

Question 14

heterolytic fission

Answer 14

most electronegative atom takes BOTH e- in the covalent bond

Question 15

alkene + steam

Answer 15

• acid catalyst
• produces alcohol

Question 16

alkene + halogen

Answer 16

dihalogenoalkane

Question 17

alkene + hydrogen halide

Answer 17

halogenoalkane

Question 18

heterolytic bond fission results in…

Answer 18

formation of IONS

Question 19

which atom is the electrophile

Answer 19

the LESS electronegative one

Question 20

describe formation of Br- with HBr reaction

Answer 20

• H is electrophile
• accepts PAIR of electrons from c=c
• h-br breaks heterolytically forming a Br- ion

Question 21

when can you have 2 diff products

Answer 21

Hydrogen halide + ASYMMETRIC alkene

Question 22

do u have equal amounts of the products?

Answer 22

no

Question 23

primary carbocation

Answer 23

C+ only bonded to ONE alkyl group (eg if its at the end of the molecule)

Question 24

secondary carbonation

Answer 24

C+ bonded to TWO alkyl groups

Question 25

which is more stable of the carbocations

Answer 25

secondary more than primary

Question 26

major product formed from

Answer 26

secondary

Question 27

markovnikoffs rule

Answer 27

the H bonds to the C attached to a greater number of H atoms

Question 28

EXPLAIN markovnikovs rule

Answer 28

• secondary carbocations are more stable
• electrons in alkyl groups can shift towards the positive charge to stabilise it
• ‘positive inductive effect’
• in secondary, positive charge is stabilised by 2 alkyl groups whereas only 1

Question 29

conditions for alkene + steam

Answer 29

• temp of 300 c
• pressure 65 atm
• phosphoric acid catalyst

Question 29

why are pi bonds weaker than sigma

Answer 29

• sigma are formed in the direct overlap of orbitals
• pi from sideways overlap of orbitals
• sideways overlap is left efficient as there is less e- density in the intermolecular space

Question 29

alkene + x solvent

Answer 29

must be non-polar organic

Question 29

state of hydrogen halide

Answer 29

gaseous

Question 29

what happens if u use a polar solvent (water)

Answer 29

• reacts with alkenes
• mixture of products is made
• one with the halide added
• one with OH added

Question 30

why can lots of product be made in free radical substitution with only a bit of UV

Answer 30

A chlorine radical is regenrated for every molecule of product formed