Alkenes Flashcards
What is the general formula for alkenes?
CnH2n (same as cycloalkanes)
What is the shape around carbon atoms in alkenes?
Trigonal planar
120 degrees
What are structural isomers?
Same molecular formula, different structural formula
What are stereoisomers?
Same molecular formula and structural formula but a different 3D arrangement
What are Pi bonds?
P orbitals on adjacent carbon atoms overlap sideways to form a Pi bond above and below the plane of bonded carbon atoms
Definition of localised electrons
Electrons that are spread over 2 atoms or less
Definition of delocalised electrons
Electrons that are spread over more than 2 atoms (Eg benzene)
How do you work out E/Z isomerism?
Circle the group on each side of the C=C with the highest atomic number
If they are the same side then (Z)
If opposite sides (E)
What 2 things do you need in order for something to display E/Z isomerism?
C=C double bond (restricted rotation)
Each carbon in C=C double bond must have 2 different groups
What other molecules can display E/Z isomerism even though they don’t have a C=C double bond
Cycloalkanes as they have restricted rotation
What do you need in order for there to be Cis/trans isomerism?
C=C double bond
Look for 1 group that is on both sides
When are things Cis isomers?
When the group that is on both sides of the C=C is the same side (both bottom/both top)
When are things Trans isomers?
When the group that is on both sides of the C=C are different sides (one bottom, one top)
What is more reactive sigma or pi bonds?
Pi bond as they are weaker so easier to break/need less energy
Also areas of high electron density so attract positive things.
What is the first step of electrophilic addition?
Add dipoles to molecule your’e adding
Draw arrow from
Double bond to delta positive atom
Bond in molecule to delta negative atom
What is the second step of electrophilic addition?
Add delta positive atom to organic
Leftover carbon is carbocation (add a +)
Draw negative ion with lone pair of e-
Draw arrow from lone pair to carbocation
What is the third step of electrophilic addition?
Draw complete structure
What is an electrophile?
Atom/group of atoms that can accept a pair of electrons forming a new covalent bond
They are attracted to areas of lots of electrons
When is Markownikov’s rule used?
When 2 or more products can be made
It is all about the stability of the carbocation and how that determines the major product
What is the most stable carbocation?
Tertiary
What is the least stable carbocation?
Primary
Which is the major product, the most stable or the least stable?
Most stable
What are polymers?
Chains made of lots of monomers (alkenes)
What are made from polymers?
Plastics and fuels
What is the reaction called when making a polymer?
Polymerisation
How do you name polymers?
Put poly(the name of the alkene used)
What happens to viscosity as saturation increases?
It increases
