Alkenes

Question 1

What is the general formula for alkenes?

Answer 1

CnH2n (same as cycloalkanes)

Question 2

What is the shape around carbon atoms in alkenes?

Answer 2

Trigonal planar

120 degrees

Question 3

What are structural isomers?

Answer 3

Same molecular formula, different structural formula

Question 4

What are stereoisomers?

Answer 4

Same molecular formula and structural formula but a different 3D arrangement

Question 5

What are Pi bonds?

Answer 5

P orbitals on adjacent carbon atoms overlap sideways to form a Pi bond above and below the plane of bonded carbon atoms

Question 6

Definition of localised electrons

Answer 6

Electrons that are spread over 2 atoms or less

Question 7

Definition of delocalised electrons

Answer 7

Electrons that are spread over more than 2 atoms (Eg benzene)

Question 8

How do you work out E/Z isomerism?

Answer 8

Circle the group on each side of the C=C with the highest atomic number
If they are the same side then (Z)
If opposite sides (E)

Question 9

What 2 things do you need in order for something to display E/Z isomerism?

Answer 9

C=C double bond (restricted rotation)

Each carbon in C=C double bond must have 2 different groups

Question 10

What other molecules can display E/Z isomerism even though they don’t have a C=C double bond

Answer 10

Cycloalkanes as they have restricted rotation

Question 11

What do you need in order for there to be Cis/trans isomerism?

Answer 11

C=C double bond

Look for 1 group that is on both sides

Question 12

When are things Cis isomers?

Answer 12

When the group that is on both sides of the C=C is the same side (both bottom/both top)

Question 13

When are things Trans isomers?

Answer 13

When the group that is on both sides of the C=C are different sides (one bottom, one top)

Question 14

What is more reactive sigma or pi bonds?

Answer 14

Pi bond as they are weaker so easier to break/need less energy
Also areas of high electron density so attract positive things.

Question 15

What is the first step of electrophilic addition?

Answer 15

Add dipoles to molecule your’e adding
Draw arrow from
Double bond to delta positive atom
Bond in molecule to delta negative atom

Question 16

What is the second step of electrophilic addition?

Answer 16

Add delta positive atom to organic
Leftover carbon is carbocation (add a +)
Draw negative ion with lone pair of e-
Draw arrow from lone pair to carbocation

Question 17

What is the third step of electrophilic addition?

Answer 17

Draw complete structure

Question 18

What is an electrophile?

Answer 18

Atom/group of atoms that can accept a pair of electrons forming a new covalent bond
They are attracted to areas of lots of electrons

Question 19

When is Markownikov’s rule used?

Answer 19

When 2 or more products can be made

It is all about the stability of the carbocation and how that determines the major product

Question 20

What is the most stable carbocation?

Answer 20

Tertiary

Question 21

What is the least stable carbocation?

Answer 21

Primary

Question 22

Which is the major product, the most stable or the least stable?

Answer 22

Most stable

Question 23

What are polymers?

Answer 23

Chains made of lots of monomers (alkenes)

Question 24

What are made from polymers?

Answer 24

Plastics and fuels

Question 25

What is the reaction called when making a polymer?

Answer 25

Polymerisation

Question 26

How do you name polymers?

Answer 26

Put poly(the name of the alkene used)

Question 27

What happens to viscosity as saturation increases?

Answer 27

It increases