Alkanes Flashcards
Saturated or unsaturated?
Saturated
What process is used to separate crude oil into different fractions?
Fractional distillation
General formula for alkanes?
CnH2n+2.
How are sigma bonds formed?
By the overlap of 2 orbitals
Why does boiling point increase as chain length increases?
There is a greater SA of contact
Stronger London forces
Why do alkanes have low reactivity?
C-C and C-H bonds sigma bonds are strong
C-C bonds are non-polar
Electronegativity of C and H is so similar- C-H bonds can be considered to be non-polar
What do curly arrow show?
The movement of the pair of electrons
What bond angle do alkanes have?
Tetrahedral
Bond angle of 109.5 degrees
Polar or non-polar?
Non-polar
Have weak temporary induced dipole-dipole forces between the molecules
Why do branched alkanes have lower boiling points than unbranched alkanes?
Temporary induced dipole-dipole forces can only operate over very short distances between 1 molecule and its neighbouring molecule
More difficult for short, bulky molecules to lie compact compared with long,thin molecules
Unbranched alkanes- Greater London forces as there is a larger SA
Why is the C-H bond stronger than the C-C bond?
The hydrogen atom only consists of one shell therefore the distance between the nuclei is shorter
There is a greater force of attraction to the nuclei and the pair of electrons around them
What is free-radical substitution?
A hydrogen atom gets substituted by a halogen (chlorine/bromine)
What is required for free radical substitution to occur?
UV light
What happens in the initiation step?
The halogen bond
Either Cl-Cl or Br-Br is broken by UV energy to form 2 radicals
What happens to the radicals in the propagation stage?
These radicals create further radicals in a chain reaction
How is the reaction terminated?
When 2 radicals collide with eachother in a termination stage
What is homolytic bond fission?
The breaking of a covalent bond with one of the bonded electrons going to each atom- forming 2 radicals
What is a radical?
A very reactive species with an unpaired electron
What is heterolytic fission?
The breaking of a covalent bond with both electrons going to the more electron negative atom- forming a cation and an anion
What is a substitution reaction?
A reaction in which an atom/group of atoms is replaced with a different atom/group of atoms
In the initiation stage, the UV light breaks which bond?
The weakest bond
Limitations: further substitution?
If a halogen radical collides with a haloalkane molecule, further H atoms can be substituted- to give a mixture of products
