CL 12- alkanes Flashcards
saturated
definition
single C-C bonds only
sigma bond
formation and rotation
formed by the direct overlap of two orbitals
can rotate freely
explain the tetrahedral shape + bond angle around each C atom in alkanes
- each C bonded to 4 other atoms
- 4 bonded pairs of electrons around carbon, which repel each other
- bond angle of 109.5°
explain the variations in boiling points of alkanes with increased C chain length
- boiling point increases
- more electrons and therefore stronger london forces
- which require more energy to overcome
explain the variations in boiling points of alkanes with increased branching
- boiling point decreases
- fewer points of contact between branched molecules compared to straight chains
- which leads to weaker london forces which require less energy to overcome
why are alkanes unreactive
2 reasons
- saturated
- non-polar
complete combustion of propane
C₃H₈ + 5O₂ –> 3CO₂ + 4H₂O
incomplete combustion of propane
C₃H₈ + 3.5O₂ –> 3CO + 4H₂O
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what are the three steps called for this mechanism?
- initiation
- propagation
- termination
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what is the name of this mechanism?
free radical substitution
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what are the conditions required for this mechanism?
UV light
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what would the initiation step be for this mechanism?
Br₂ –> 2Br.
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what would the propagation steps be for this mechanism?
C₂H₆ + Br. –> .C₂H₅ +HBr
.C₂H₅ + Br₂ –> C₂H₅Br + Br.
C₂H₆ + Br₂ –> C₂H₅Br +HBr
what would the three termination steps be for this mechanism?
- 2.C₂H₅ –> C₄H₁₀
- 2Br. –> Br₂
- Br. + .C₂H₅ –> C₂H₅Br
limitations of radical substitution in synthesis
- not a good way to synthesise a haloalkane as the yield of the product is low, due to additional products formed from termination steps
- substitution of the halogen can occur anywhere along the alkane chain, forming lots of different isomers
