Alkenes Flashcards
Alkenes:
What are Alkenes?
Unsaturated HC
Alkenes: Bonds in Organic Molecules
When are Covalent Bonds formed?
When atomic orbitals from diff atoms overlap
↳ electrons are shared
Alkenes: Bonds in Organic Molecules
Why is a Covalent Bond formed?
Nuclei of the atoms are attracted by electrostatic attraction to the bonding electrons
Alkenes: Bonds in Organic Molecules
What are Sigma Bonds?
(σ-bond)
Single Covalent bonds in organic mol
Alkenes: Bonds in Organic Molecules
How is a Sigma Bond formed?
When 2 orbitals overlap in a straight line between 2 atoms
Alkenes: Bonds in Organic Molecules
Why do Sigma Bonds have a High Bond Enthalpy?
There’s a strong electrostatic attraction between the nuclei & shared electrons
↳ they’re the strongest Covalent Bond
Alkenes: Bonds in Organic Molecules
Why are Sigma Bonds strong?
There is a high electron density between the nuclei & shared electrons
Alkenes: Bonds in Organic Molecules
What is a Double Covalent bond made up of?
- Pi Bond
- Sigma Bond
Alkenes: Bonds in Organic Molecules
How is a Pi Bond formed?
2 lobes of 2 orbitals overlap sideways
↳ 1 above & 1 below
Alkenes: Bonds in Organic Molecules
Why are Pi Bonds weaker?
They have a low electron density between the nuclei & shared electrons
↳ spread out above & below
Alkenes:
Why can’t double bonds rotate?
They’re arranged to be Trigonal Planar
Alkenes: Stereoisomerism
What is Stereoisomerism?
Compounds with the same structural formula but different arrangement in space
Alkenes: Stereosiomerism
Where is the C=C located in an Alkene?
In the longest chain
Alkenes: Stereosiomerism
When is E/Z used?
When each carbon have 2 different groups attached to them
Alkenes: Stereosiomerism
What is an E-Isomer?
When the same priority groups positioned diagonally
Alkenes: Stereosiomerism
What is an Z-Isomer?
When the same priority group are on the same side of the double bond
Alkenes: Stereosiomerism
What are Priority Groups?
Compound w a higher atomic number are given higher priority
Alkenes: Stereosiomerism
Why are Priority Groups used?
- To figure out the name of the molecule
- To figure out which E/Z isomer it is
Alkenes: Stereosiomerism
How do u work out the Priority Group if the C is directly bonded to 2 other C?
The group bonded w more C has higher priority
Alkenes: Stereosiomerism
What do u look for in Cis-Trans Isomers?
How identical groups are positioned
Alkenes: Stereosiomerism
When do you use Cis-Trans Isomerism?
When there’s at least 1 common group on the compound
Alkenes: Stereosiomerism
What is Cis Isomerism?
(same)
When the identical groups are on the same side of the double bond
Alkenes: Stereosiomerism
What is Trans Isomerism?
(different)
When the identical groups are on opposite sides of the double bond
Alkenes: Reaction of Alkenes
What is Electrophillic Addition?
When the double bond opens up & atoms are added to the C atoms
Alkenes: Reaction of Alkenes
What does the C=C contain?
Its rich in electrons : it attracts electrophiles (something that is + or δ+)
Alkenes: Reaction of Alkenes
What is Hydrogeneration?
Alkene + Hydrogen → Alkane
Adding hydrogen to C=C bond produces an alkane
* Margerene is made
Alkenes: Reaction of Alkenes
What is Steam Hydration?
Alkene + Water → Alcohol
Adding steam to an alkene to form an alcohol
* 300°C
* 60 atm
* Phosphoric Acid Catalyst
Alkenes: Reaction of Alkenes
Alkenes are Oxidised by Acidified Potassium Manganate (VII)
The purple colour of K becomes decolourised making a diol
↳ alcohol that has 2 OH groups
Alkenes: Reaction of Alkenes
Halogens React w Alkenes to form Dihalogenoalkanes
(Beginning)
- Alkene moves towards Br
↳ causing them to repel - But if pushing force > repulsion
↳ Br becomes polarised → e- from Br moves to the 2nd Br : induces a polar bond
Alkenes: Reaction of Alkenes
Halogens React w Alkened to form Dihalogenoalkanes
(Intermediate)
- C=C breaks as its attracted to Br
- Br bond is broken
Alkenes: Reaction of Alkenes
Halogens React w Alkenes to form Dihalogenoalkanes
(End)
- Place Br by a C atom
↳ C has 4 bonds - Add a + to the other carbon
↳ creating a C+ cation - But there’s still a free Br-
↳ attaches to C+
Alkenes: Alkenes undergo Addition with Hydrogen Halides
How are Halogenoalkanes formed?
(equation)
Alkenes: Markownikoff & Carboncation Stability
How do you workout if a Carboncation is Primary,Secondary or Tertiary?
- Locate C+ cation
- Look for how many alkyl groups are attached to it
Alkenes: Markownikoff & Carboncation Stability
What is an Alkyl Group?
(R)
An alkane w one less H
Alkenes: Markownikoff & Carboncation Stability
What is a Primary Carboncation?
C+ cation is only 1 attached alkyl group
Alkenes: Markownikoff & Carboncation Stability
What is a Secondary Carboncation?
C+ cation is attached to 2 alkyl groups
Alkenes: Markownikoff & Carboncation Stability
What is a Tertiary Carboncation?
C+ cation is attached to 3 alkyl groups
Alkenes: Markownikoff & Carboncation Stability
How would you stabilise a Carboncation?
By donating electrons through attaching more alkyl groups
The more alkyl groups, the more stable : the longer that reaction as + & + make bonds quicker
Alkenes: Markownikoff & Carboncation Stability
How would you determine which product is Major/Minor?
Major: Most stable product
Minor: Less stable product
Alkenes: Polymers
Whats a Monomer?
A small unit
Alkenes: Polymers
What is a Polymer?
Long chains
Alkenes: Polymers
What is Addition Polymerisation?
monomer → repeat unit → polymer
When the alkene double bond breaks & joins together into polymers
Alkenes: Different methods for Disposing Polymers
How are Waste Plastics Buried?
Landfill only when the plastic is difficult to separate or recycle
Alkenes: Different methods for Disposing Polymers
What is an Advantage of Burying Waste Plastics?
Easily removed
Alkenes: Different methods for Disposing Polymers
What is a Disadvantage of Burying Waste Plastics?
Space used for vegetation is used up
Alkenes: Different methods for Disposing Polymers
How are Waste Plastics Reused?
- Many plastics are made from non-renewable sources so they’re reused
- Some are re-moulded into others
↳ cracked into monomers or used as feedstock
Alkenes: Different methods for Disposing Polymers
What are the Advantages of Cracking Waste Plastics?
Forms alkenes
↳ new useful plastics
Alkenes: Different methods for Disposing Polymers
What are the Disadvantages of Cracking Waste Plastics?
High heat is needed for cracking → higher costs
↳ other chemicals released
Alkenes: Different methods for Disposing Polymers
What are the Advantages of Remoulding?
New objects are formed
Alkenes: Different methods for Disposing Polymers
What are the Disadvantages of Remoulding?
Time consuming
Alkenes: Different methods for Disposing Polymers
How are Waste Plastics Burned?
Last Resort: heat generated can be used for electricity
↳ releases toxic gases such as HCl
Alkenes: Different methods for Disposing Polymers
What are the Advantages of Burning Waste Plastics?
Heat is given off
Alkenes: Different methods for Disposing Polymers
What are the Disadvantages of Burning Waste Plastics?
Non-reusable source used e.g oil
↳ releases emissions
Alkenes: Sustainability
What is Sustainability?
Saving something for the long term usage
Alkenes: Sustainability
How to ensure the Design of Suitable Polymers?
- Use molecules that are safe & environmentally friendly
- Use renewable where possible
- Use minimum amount of energy
- Limit waste products
Alkenes: Sustainability
What are Biodegradable Polymers?
Polymers that break down naturally
Alkenes: Sustainability
What are the Advantages of using Renewable Materials?
- They won’t run out
- They’re carbon neutral
