Isomerism Flashcards
What does a mechanism show?
How a reaction happens
What are mechanisms
Mechanisms are diagrams that break reactions down into individual stages by using curly arrows to show which bonds
are made or broken
What happens in order to make or break a bond
Electrons have to move around
How do we show how electrons move around?
A curly arrow shows where a pair of electrons goes during a reaction. Starts at the lone or bond pair
What are Isomers
Two molecules are isomers of one another if they have the same molecular formula but the atoms are arranged differently
What are the two types of isomers you need to know
• Structural isomers
• Stereoisomers
What are structural isomers and give types
• Same molecular formula but different structural formulas
• Chain isomers
• Positional Isomers
• Functional group isomers
Define structural isomers
Different arrangements of the carbon skeleton. Some are straight chains and some are branched in many different ways
Define positional isomers
Same skeleton and atoms or groups of atoms but atom or group of atom is attached to a different carbon atom
Define functional group isomers
Same atoms arranged into different functional groups
What are stereoisomers
Same structural formula but different arrangement in space
Give an example of a functional group with double bonds and the effect of this
• 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
Describe the z-isomer
The same groups either have both above or both below the double bond
Describe the E-isomer
Has the same groups positioned across the double bond
What does E on E-isomer stand for?
‘Entgegen’ which German for opposite
What Z on Z-isomer stand for?
‘Zusammen’ for together
How do we work an E/Z isomer surrounded by 3 or 4 different groups
Using the Cahn-Ingold-Prelog (CIP) priority rules
Describe how to find an E/Z isomer using Cahn-Ingold-Prelog priority rule
• 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
What do you do when the atoms directly bonded to the carbon are the same
• you have to look at the next atom in the groups to work out which has the higher priority
How is the pollutant carbon dioxide formed, what is the problem caused and how can this problem be reduced?
• Complete combustion of fuels containing C
• Greenhouse gas
• Burn less fossil fuels
How is the pollutant carbon monoxide formed, what is the problem cause and how can the problem be reduced
• Incomplete combustion of fuels containing C
• Toxic
• Ensure a good supply of oxygen when burning fuels
How is the pollutant C (soot) formed, what is the problem caused and how can the problem be reduced
• Incomplete combustion of fuels containing C
• blackens buildings, can cause respiratory problems, global dimming
• Ensure a good supply of oxygen when burning fuels
How is water formed, what problem does it cause and how can the problem be reduced
• Combustion of fuels containing H
• Not a problem
• N/A
How is sulfur dioxide formed, what problem does it cause and how can the problem be reduced
• Combustion of S containing compounds in fuel
• Acid rain
• Removes S from fuel before burning, flue gas desulfurization
How is nitrogen dioxide formed, what problem does it cause and how can the problem be reduced
• 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
How is the pollutant unburned hydrocarbons formed, what problem does it cause and how can the problem be reduced?
• Some of the fuel may not actually burn
• Wastes fuel
• Ensure engines are well tuned and there is a good supply of oxygen
What is the difference between cracking and fractional distillation
- 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
Why do larger hydrocarbons have a high boiling point?
Due to the length of their carbon chain which means increased vander waals forces of attraction
Where are flue gases produced from?
Gases produced from chimneys or industrial waste
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
• 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
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)
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
Draw three branched chain isomers of C5H10Br2
Check physical flashcards for answers
Which compound is a structural isomer of Z-but-2-ene
- Butane
- E-but-2-ene
- cyclobutane
-methylbut-2-ene
Cyclobutane
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
- Chloroalkane would have a faster rate of hydrolysis
- C-Cl stronger than C-Br
