reactions of alkenes

Question 1

what shape is a cycloalkane

Answer 1

ring

Question 2

what shape is an aliphatic alkene

Answer 2

straight chain

Question 3

if you have an aliphatic alkene and a cycloalkene and they are in the same series what does this mean in terms of their reactions

Answer 3

same series = similar reactions

Question 4

why are alkenes so reactive in terms of bond enthalpy

Answer 4

it takes less energy to break a double bond into a single bond as you are easily only breaking the Pi bond

Question 5

why do all alkenes have a trigonal planar shape

Answer 5

there are 3 regions of electron density around c atoms which repel each other equally to reduce repulsion

this gives a trigonal planar shape with 120 degrees and all atoms in the same plane

Question 6

why are alkenes insoluble in polar solvents

Answer 6

alkenes are non polar so have no overall dipole

Question 7

why do alkenes have a lower boiling point than alkanes in terms of electrons

Answer 7

2 less hydrogens, less electrons causing weaker vdw which require less energy to overcome

Question 8

when an alkene undergoes an addition reaction what does it form

Answer 8

1 product from 2 molecules

unsaturated alkene becomes a saturated product

Question 9

what type of catalyst is needed for the hydrogenation of ethene

Answer 9

nickel catalyst

Question 10

give 2 examples of types of alkene addition reaction

Answer 10

hydrogenation
halogenation

Question 11

explain the result of the reaction between bromine water and an alkene

Answer 11

alkene decolourises bromine water

Question 12

what is the IUPAC name for the product formed when

ethene reacts with bromine water

Answer 12

1,2- dibromoethane

Question 13

define electrophiles

Answer 13

Electron pair acceptor in an organic mechanism that is attracted to electron dense areas

Question 14

to be an electrophile what properties does the element have to have

Answer 14

polar
OR
positive charge
OR
induced dipole

Question 15

in the electrophilic addition between ethene and bromine

why is bromine an electrophile

Answer 15

bromine has an induced dipole

Question 16

define heterolytic fission

Answer 16

breaking of a covalent bond where both bonding electrons go to 1 atom

Question 17

define mechanism

Answer 17

sequence of steps to show the path taken by electrons in a reaction

Question 18

define carbocation

Answer 18

an organic ion in which a carbon atom has a positive charge

Question 19

name the 3 types of carbocation

Answer 19

primary
secondary
tertiary

Question 20

what happens in terms of stability when the number of alkyl groups on the positively charged carbon atom

Answer 20

stability of carbocations increases as the number of alkyl groups on the positively charged carbon atom increase

Question 21

why does stability of molecules increase when there are more alkyl groups on the positively charged carbon atom

Answer 21

• alkyl (R groups) contain a greater electron density than hydrogen atoms
• this density is attracted towards and reduces the positive charge on the carbon atom which has a stabilising effect

Question 22

what is Markonikov’s rule

Answer 22

when a compound Hx (halide) is added to an unsymmetrical alkene
the hydrogen becomes attached
to the carbon with the most hydrogen already attached to it