Isomerism

Question 1

What does a mechanism show?

Answer 1

How a reaction happens

Question 2

What are mechanisms

Answer 2

Mechanisms are diagrams that break reactions down into individual stages by using curly arrows to show which bonds
are made or broken

Question 3

What happens in order to make or break a bond

Answer 3

Electrons have to move around

Question 4

How do we show how electrons move around?

Answer 4

A curly arrow shows where a pair of electrons goes during a reaction. Starts at the lone or bond pair

Question 5

What are Isomers

Answer 5

Two molecules are isomers of one another if they have the same molecular formula but the atoms are arranged differently

Question 6

What are the two types of isomers you need to know

Answer 6

• Structural isomers
• Stereoisomers

Question 7

What are structural isomers and give types

Answer 7

• Same molecular formula but different structural formulas
• Chain isomers
• Positional Isomers
• Functional group isomers

Question 8

Define structural isomers

Answer 8

Different arrangements of the carbon skeleton. Some are straight chains and some are branched in many different ways

Question 9

Define positional isomers

Answer 9

Same skeleton and atoms or groups of atoms but atom or group of atom is attached to a different carbon atom

Question 10

Define functional group isomers

Answer 10

Same atoms arranged into different functional groups

Question 11

What are stereoisomers

Answer 11

Same structural formula but different arrangement in space

Question 12

Give an example of a functional group with double bonds and the effect of this

Answer 12

• Alkenes
• Double bonded carbons and atoms bonded to these carbons lie on the same plane
• They can’t rotate and bend because they are rigid
• Restricted rotation causes stereoisomerism called E/Z isomerism

Question 13

Describe the z-isomer

Answer 13

The same groups either have both above or both below the double bond

Question 14

Describe the E-isomer

Answer 14

Has the same groups positioned across the double bond

Question 15

What does E on E-isomer stand for?

Answer 15

‘Entgegen’ which German for opposite

Question 16

What Z on Z-isomer stand for?

Answer 16

‘Zusammen’ for together

Question 17

How do we work an E/Z isomer surrounded by 3 or 4 different groups

Answer 17

Using the Cahn-Ingold-Prelog (CIP) priority rules

Question 18

Describe how to find an E/Z isomer using Cahn-Ingold-Prelog priority rule

Answer 18

• Assign a priority to the two atoms attached to each carbon in a double bond
• The atom with the highest atomic number on each number is given the highest priority
• Now work out which isomer you have, just look at how the two higher priority groups are arranged

Question 19

What do you do when the atoms directly bonded to the carbon are the same

Answer 19

• you have to look at the next atom in the groups to work out which has the higher priority

Question 20

How is the pollutant carbon dioxide formed, what is the problem caused and how can this problem be reduced?

Answer 20

• Complete combustion of fuels containing C

• Greenhouse gas

• Burn less fossil fuels

Question 21

How is the pollutant carbon monoxide formed, what is the problem cause and how can the problem be reduced

Answer 21

• Incomplete combustion of fuels containing C

• Toxic

• Ensure a good supply of oxygen when burning fuels

Question 22

How is the pollutant C (soot) formed, what is the problem caused and how can the problem be reduced

Answer 22

• Incomplete combustion of fuels containing C

• blackens buildings, can cause respiratory problems, global dimming

• Ensure a good supply of oxygen when burning fuels

Question 23

How is water formed, what problem does it cause and how can the problem be reduced

Answer 23

• Combustion of fuels containing H

• Not a problem

• N/A

Question 24

How is sulfur dioxide formed, what problem does it cause and how can the problem be reduced

Answer 24

• Combustion of S containing compounds in fuel

• Acid rain

• Removes S from fuel before burning, flue gas desulfurization

Question 25

How is nitrogen dioxide formed, what problem does it cause and how can the problem be reduced

Answer 25

• Reaction of N2 in the air with O2 in the at very high temperatures (in engines and furnaces)

• Acid rain

• Use catalytic converters in cars

Question 26

How is the pollutant unburned hydrocarbons formed, what problem does it cause and how can the problem be reduced?

Answer 26

• Some of the fuel may not actually burn

• Wastes fuel

• Ensure engines are well tuned and there is a good supply of oxygen

Question 27

What is the difference between cracking and fractional distillation

Answer 27

• Cracking is the process used to break down large hydrocarbons into smaller hydrocarbons
• Fractional distillation is the process used to separate components of crude oil

Question 28

Why do larger hydrocarbons have a high boiling point?

Answer 28

Due to the length of their carbon chain which means increased vander waals forces of attraction

Question 29

Where are flue gases produced from?

Answer 29

Gases produced from chimneys or industrial waste

Question 30

Explain the differences between structural isomerism and stereoisomerism. Use examples to show how compounds with molecular formula C4H8 exhibit stereoisomerism and the three types of structural isomerism

Answer 30

• Structural isomers: molecules with the same molecular formula but different structure
• Stereoisomers: molecules with the same structural formula but different arrangement of atoms in space
• Stereoisomers lack rotation around C=C
• structures of E and Z-but-2-ene
• structural isomers:
- different c chain e.g methylpropene, but-1-ene, but-2-ene
- different position of functional groups e.g but-1-ene, but-2-ene
- different functional group e.g cyclobutane and but-1-ene, but-2-ene, methylpropene

Question 31

Compounds A,B and C all have the molecular formula C5H10

A and B decolourise bromine water but C does not.

B displays stereoisomerism but A does not

Use this information to deduce a possible structure for each of compounds A,B and C and explain your deductions

State the meaning of the term stereoisomers and explain how they arise in compound B (6 marker)

Answer 31

Stage-1 deduces which compounds are saturated and unsaturated
• States that A and B are unsaturated/do contain C=C/ alkenes
• As they decolourise in bromine water
• States that C is saturated/does not contain C=C/ is a cycloalkane
• As it does not decolourise in water

Stage-2 deduces the structures
• A- pent-1-ene
• 2-methylbut-1-ene
• 3-methylbut-1-ene
• 2-methylbut-2-ene
B- pent-2-ene
C- cyclopentane, methylcyclobutane

Stage-3 can explain the stereoisomerism
• Definition of stereoisomers
• C=C can’t rotate explanation
• How it arises that each C in C=C has two different groups

Question 32

Draw three branched chain isomers of C5H10Br2

Answer 32

Check physical flashcards for answers

Question 33

Which compound is a structural isomer of Z-but-2-ene

• Butane
• E-but-2-ene
• cyclobutane
  -methylbut-2-ene

Answer 33

Cyclobutane

Question 34

A student decides to prepare alcohol A using the same method as in (d) but using the chloroalkane (CH3)2CHCH2CH2Cl instead of bromoalkane. State and explain how the rates of hydrolysis of the chloroalkane and the bromoalkane would differ

Answer 34

• Chloroalkane would have a faster rate of hydrolysis
• C-Cl stronger than C-Br