Isomerism Flashcards
What are “structural isomers?”
- Structural isomers have the same molecular formula but a different structural formula.
What are the 3 types of structural isomers?
- Chain
- Position
- Functional group
What are “chain isomers?”
- Same molecular formula but different arrangement of the carbon skeleton.
What are “positional isomers?”
- Same molecular formula but different position of the functional group on the carbon skeleton.
What are “functional group isomers?”
- Same molecular formula but different functional group.
Give 3 examples of different molecules that would be functional group isomers .
Cycloalkanes — alkene
Aldehydes —- Ketones
Alcohols —- ethers
What are “stereoisomers?”
- Same structural formula but different arrangement of atoms in space.
True or False
Molecules with single bonds between carbon atoms cannot rotate.
- FALSE
- Molecules can rotate freely around single C-C bonds.
Can molecules rotate around C=C double bonds
- No.
- Molecules can’t rotate around C=C double bonds (ie. the atoms around the C=C double bond are in a fixed position.)
() - extra info for clarification.
How can you tell if 2 molecules are stereoisomers of each other?
- Can’t twist double bond to turn one isomer into another (as atoms can’t rotate around the C=C double bond.)
- Atoms bonded directly to the double bond are flat/ planar.
What terminology do we use to describe how atoms can’t rotate around the rigid C=C double bond?
- We say there is “restricted rotation” around the C=C double bond.
When do we get E/Z isomerism?
- When you have two different atoms/ groups of atoms attached to the same carbon.
- Restricted rotation about the planar carbon-carbon double bond.
What is meant when we say a molecule is a Z molecule (using E-Z notation?)
- Z: two priority groups are on the same side of the double bond.
What is meant when we say a molecule is a E molecule (using E-Z notation?)
E: the priority groups on opposite sides of the double bond.
When could we call a molecule cis/ trans?
- Cis: two of same groups on same side of double bond.
- Trans: two of the same groups on opposite sides of double bond.
What form of isomerism is E-Z isomerism?
- E-Z isomerism is a form of stereoisomerism.
When are CIP priority rules applied to a molecule?
- CIP rules are applied when deciding if an isomer is E or Z when 2 different groups are bonded to the SAME carbon atom.
How would you determine if a molecule is an E/Z isomer when there are 4 DIFFERENT groups around the C=C double bond?
- Split molecule in half.
- Work out atomic number of first element DIRECTLY BONDED to C=C double bond –> atom with highest atomic number is given higher priority.
- Two higher priority groups same side of double bond: Z
- Two higher priority groups on opposite sides of double bond: E.
What do you do when determing whether molecules are E/Z isomers, 4 different groups around C=C double bond AND element DIRECTLY BONDED to C=C double bond is the same?
- Do normal steps.
- When you reach the two atoms DIRECTLY BONDED to the C=C double bond that have same atomic no, look at the next atom down the chain, if they are still the same, keep going down the chains until one atom’s atomic no is greater than the other atom’s - this will be the higher priority group.
What does CIP priority rules stand for?
Cahn–Ingold–Prelog (CIP) priority rules
What do ethers look like? What would be the name of an ether with two ethy groups?
- Oxygen in middle of carbon chain with carbons on either side of the chain.
- 2 ethyl groups on either side of the O = Ethoxyethane.
How do we name ethers? Prefix/ suffix?
- Prefix: Alkyloxy at the beginning of the name - ie. it would be arranged in alphebetical order (e.g., if there was bromine group, it would be written before an ethyloxy group for EXAMPLE.)
() - extra
When does E-Z isomerism actually occur?
- C=C double bond present.
- Two different groups on EACH side of the molecule (the groups don’t have to ALL be different, just different on each side.)
When does cis/ trans isomerism occur?
- Will occur when there’s an identical group on either side of the C=C double bond.
How should we always display groups attached to carbon atoms?
- Always display them as structural formulae (not molecular!)
How many isomers do each of these molecules have:
1.) C₄H₁₀
2.) C₅H₁₂
3.) C₆H₁₄
Gautum said learning these 3 will be useful for the exam.
1.) 2 isomers
2.) 2 isomers
3.) 5 isomers.
What does E/Z isomerism occur as a result of?
- E/z isomerism occurs as a result of restricted rotation about the planar carbon - carbon double bond.
