M4 - Alkenes

Question 1

Alkenes are which kind of hydrocarbons?

Answer 1

Unsaturated

Question 2

What is the systematic name of hydrocarbon A?

Answer 2

3-methylhex-2-ene

Question 3

Name compound C: CH₃CH₂CH=CHCH₂CH₂OH

Answer 3

Hex-3-en-1-ol

Question 4

What is the general formula and the suffix used for naming alkenes?

Answer 4

C_nH_2n
-ene

Question 5

What prefixes are used when there is more than one alkene group, and any other addtions we might need to make to the name?

Answer 5

• Use ‘di-‘, ‘tri-‘, ‘tetra-‘, etc.
• Add an ‘a’ after the stem
  For example, octa-1,4-diene

Question 6

How do you determine the parent chain when naming organic compounds?

Answer 6

Find the longest C chain that includes the alkene group.

Question 7

What is the rule for numbering the parent chain in alkene naming?

Answer 7

Give the lowest number possible for the alkene group.

Question 8

Define the term structural isomers?

Answer 8

Compounds with the same molecular formula but different structural formulae.

Question 9

Define the term stereoisomers?

Answer 9

Compounds with the same structural formula but with different arrangement of atoms in space.

This includes E/Z and cis/trans isomers.

Question 10

How should alkyl groups be named in the alkene naming process?

Answer 10

Name and number any alkyl groups, listing them in alphabetical order if multiple, for example, 2-ethyl-3-methylheptane.

Question 11

What prefix is used for naming cyclic alkenes?

Answer 11

‘cyclo-‘

This indicates the presence of a closed ring of carbon atoms.

Question 12

What is the major product formed from the electrophilic addition of HBr to propene?

Answer 12

2-bromopropane

It is formed from a secondary carbocation intermediate which is more stable.

Question 13

What is Markownikoff’s Rule?

Answer 13

This leads to the formation of a more stable carbocation intermediate

Question 14

What are the five main reactions of alkenes?

Answer 14

1. Halogenation e.g. bromination / chlorination
2. Hydrogenation
3. Hydration
4. Addition of a Hydrogen Halide

Each reaction has specific reagents and conditions.

Question 15

What is the chemical test for an alkene functional group?

Answer 15

• Add bromine water
• Solution turns from orange to colourless

This indicates the presence of a C to C double bond.

Question 16

What are the problems associated with the disposal of addition polymers?

Answer 16

• Non-biodegradable
• Burning produces toxic gases

Question 17

What are some sustainable ways to process waste polymers?

Answer 17

• Recycled (to make other plastic materials)
• Combustion for energy production
• Use as an organic
• Removal of toxic waste products

Question 18

How can polymers minimize environmental damage?

Answer 18

• Develop biodegradable polymers
• Develop photodegradable polymers

Question 19

What are the Cahn-Ingold-Prelog (CIP) Priority Rules?

Answer 19

Atoms attached to carbon atoms of the double bond are given priority based on atomic number

This helps in determining E/Z isomerism

Question 20

What is the criteria for a compound to be a Z isomer?

Answer 20

The groups of higher priority are on the same side (zee zame zide) of the double bond.

Question 21

What is the criteria for a compound to be a E isomer?

Answer 21

The groups of higher priority are on diagonally opposite sides of the double bond.

Question 22

What criteria must be met for cis/trans isomers?

Answer 22

• Must have a carbon-carbon double bond, has restricted rotation
• Each carbon must have two different groups attached
• Two groups must be identical (often a H, one on each C of the C=C)

This includes common examples like 2-butene

Question 23

Define the term electrophile

Answer 23

An electron pair acceptor

Electrophiles are essential in electrophilic addition reactions.

Question 24

Draw a labelled diagram to show the formation of the π-bond.

Answer 24

• (sideways) overlap of p orbitals ✓
• (labelled) diagram on right showing π-bond ✓

Question 25

Explain what is meant by the terms **σ-bond** and **π-bond.**

Answer 25

* **σ-bond:** Overlap of orbitals between (bonding) atoms ✓ * **π-bond**: Sideways overlap of (adjacent) p-orbitals ✓

Question 26

How many **σ- and π-bonds** are in one molecule of **buta-1,3-diene?**

Answer 26

* σ-bonds = 9 * π-bonds = 2

Question 27

**Propene, C₃₆**, has **different bond angles and shapes** around the carbon atoms. The displayed formula of a propene molecule is shown below. Predict the **bond angles and the names of the shapes** around the C atoms 1 and 2 above, and **explain why the bond angles and shapes are different.** **[5]**

Answer 27

* C1 = 109.5° & tetrahedral ✓ * C2 = 120° & trigonal planar ✓ * In C1/109.5°, 4 bonded pairs/bonding regions/bonds ✓ * In C2/120°, 3 bonded regions/bonds ✓ * Electron pairs/bonded pairs repel (as far apart as possible) ✓

Question 28

What is the number of **σ-bonds** in the molecule below?

Answer 28

9

Question 29

What is the **mechanism for addition reactions?**

Answer 29

Electrophilic Addition

Question 30

Compound **D,** shown below, reacts with hydrogen bromide by **electrophilic addition.** A mixture of two organic compounds, **E and F,** is formed. Outline the mechanism of the reaction between **compound D** and **hydrogen bromide** to form either compound E or compound F. Include curly arrows and relevant dipoles. **[3]** Which of **E or F** is the **major organic product?** Explain your answer. **[1]**

Answer 30

SEE MECHANISM ATTACHED **(3 MARKS)** FOR: * Curly arrow from C=C bond to H of H–Br ✓ * Correct dipole shown on H–Br **AND** curly arrow showing the breaking of H–Br bond ✓ * Correct carbocation **AND** curly arrow from Br^- to C⁺ of carbocation ✓ * 2-bromo-2-methylpentane **AND** (the) carbocation intermediate (in the formation of 2-bromo-2-methylpentane) is more stable (than the carbocation in the formation of the other product) ✓

Question 31

What **criteria** must be met for **E/Z isomers?**

Answer 31

* Must have a carbon-carbon double bond, has restricted rotation * Each carbon of the C=C must have two different groups attached

Question 32

Outline the **reaction mechanism** for the reaction of **(CH₃)₃CCH=CH₂ and bromine.** Include curly arrows and relevant dipoles, the structure of the product and the name of the mechanism **[4].**

Answer 32

Question 33

The chemists decide to use **compound E**, shown below, as the monomer. Draw a section of the polymer formed, *showing two repeat units,* and suggest why this polymer is likely to be soluble in water **[2].**

Answer 33

* OH/alcohol groups form hydrogen bonds with water ✓

Question 34

The **repeat unit** of an addition polymer is shown below.

Answer 34

A

Question 35

Which **structure** shows a section of **poly(propene)?**

Answer 35

D

Question 36

**Compound C** *(shown below)* forms an addition polymer E. Write a balanced equation for this reaction. Show displayed formulae. **[2]**

Answer 36

Question 37

Disadvantage of using combustion as a method for the disposal of waste polymer, **poly(1,1-dichloroethene) [1].**

Answer 37

Formation of HCl/products of combustion cause acid rain *OR* Formation of CO₂/gases that cause global warming / greenhouse gases *OR* Formation of CO ✓

Question 38

Hex-2-ene shows **E/Z isomerism.** Draw the **skeletal formulae** of E-hex-2-ene and Z-hex-2-ene **[2].** State and explain the **features** of a hex-2-ene molecule that **lead to E and Z isomers [2].**

Answer 38

* (carbon-carbon) double bond does not rotate OR has restricted rotation ✓ * Each carbon atom of the double bond attached to (two) different groups / atoms ✓

Question 39

Answer 39

C

Question 40

Complete the **flowchart** to show the missing reagents, catalysts and the structures of organic products **[4].**

Answer 40

Question 41

Complete the **flowchart** to show the structures of the organic products of these reactions **[3].**

Answer 41