Topic B3 - Alkenes

Question 1

What bonds are present in alkenes?

Answer 1

-sigma bonds
-pi bonds

Question 2

What is the shape of each c–c bond and its bonded hydrogens?

Answer 2

-trigonal planar
-120
-4 bonding pairs
-2 single bonds, 1 double bond
-double bond repels more than single bond

Question 3

Why is pi bond weak?

Answer 3

electron density spread over a wider distance

Question 4

Where is pi bond found?

Answer 4

double carbon-carbon bond

Question 5

What does stereoisomers mean?

Answer 5

same structural formular but a different arrangement of atoms in space

Question 6

How does stereoisomerism arise?

Answer 6

due to rotation around double bond being restricted, so groups around carbon are fixed to each other

Question 7

How do you identify E isomerism?

Answer 7

-ensure both sides of double bond contain 2 different side chains
-assign priority groups (highest atomic number = top priority)
-if top priorities are on different sides, then it is E isomerism

Question 8

How do you identify Z isomerism?

Answer 8

-ensure both sides of double bond contain 2 different side chains
-assign priority groups (highest atomic number = top priority)
-if top priorities are on same side, then it is Z isomerism

Question 9

Addition reactions: with hydrogen conditions

Answer 9

-hydrogen
-nickel catalyst
-423k (temp)

Question 10

Addition reactions: with hydrogen example

Answer 10

propene ——> propane

Question 11

Addition reactions: with steam conditions

Answer 11

-add steam
-phosphoric acid catalyst (or conc. sulfuric acid)

Question 12

Addition reactions: with steam example

Answer 12

propene + steam —-> propan-1-ol or propan-2-ol

Question 13

Addition reactions: with hydrogen halides conditions

Answer 13

-room temperature
-gaseous hydrogen halide

Question 14

Addition reactions: with hydrogen halide example

Answer 14

prop-1-ene + hydrochloric acid —-> 1-chloropropane or 2-chloropropane

Question 15

What is an electrophile?

Answer 15

electron pair acceptor

Question 16

What do curly arrows in an electrophile mechanism show?

Answer 16

movement of electron pairs

Question 17

How do you work out the major product of a reaction?

Answer 17

-more stable carbocation
-more alkyl groups attached to charged carbon atom, means charge is more spread out so ion is more stable

Question 18

What bond breaks during addition polymerisation?

Answer 18

double bond (pi bond)

Question 19

How are waste polymers used for energy production?

Answer 19

-combustion
-incinerated to produce heat
-generates steam to turn turbine

Question 20

How are waste polymers used for organic feedstock?

Answer 20

-chemical and thermal processes reclaim monomers
-materials produced as raw materials for new polymers

Question 21

How is toxic waste removed from waste polymers?

Answer 21

solvents dissolve polymer and precipitation of solvent removes polymer

Question 22

Biodegradable polymers

Answer 22

-broken down by microorganisms to produce carbon dioxide/ water/ biological compounds
-compostable polymers leave no toxic residue (e.g. shopping bags made from plant starch)

Question 23

Photodegradable polymers

Answer 23

bonds weakened by absorbing light