alkanes Flashcards
Which important bonds are freely rotating in organic chemistry
Single C-C and C-H bonds.
What 2 factors affect the boiling points of a homologous series?
- Length of the main chain:
○ Longer ∴ MORE London forces ∴ stronger the
attraction ∴ more energy required to overcome. - Surface area of contact:
○ Greater ∴ MORE London forces ∴ stronger the attraction ∴ more energy required to overcome.
branching reduces this
Give 2 reasons why organic compounds are mostly unreactive
● C-C and C-H have high bond enthalpies.
● Very low bond polarity (essentially nonpolar).
What is incomplete combustion, what does this form, and what does this mean in terms of energy?
● Combustion under limited oxygen forming CO and/or C (soot).
● Produces less energy per mole (as less energy is released from bond making)
What is cracking?
● Converting long chain hydrocarbons to smaller ones.
● High Mr alkane → small Mr alkane + alkene.
Describe the 3 steps of the synthesis of chloroalkanes (using methane)
- Initiation - UV light is supplies enough energy to break Cl-Cl bonds by homolytic fission.
- Propagation - chlorine radicals remove H atoms from methane to form methyl radicals. These react with Cl2 molecules to form a chloromethane and Cl•. The new radical continues the chain reaction.
- Termination - when all radicals meet other radicals.
Give 2 problems with synthesising haloalkanes by free radical substitution
Lots of termination steps lead to impurities (e.g., 2 •CH3 meeting).
Further substitution of termination products.
Describe the process of fractional distillation
Heat the crude oil to the highest boiling point.
Funnel the vapours into a fractionating column which is cooler further up.
Let the hydrocarbons will rise up and condense and their respective b.p.’s.
state the shape and bond angle around each carbon in propene
tetrahedral around CH3 bond angle 109.5
trigonal planar around each C in C=C bond angle 120
