Alkanes Flashcards
What are the suffixes related to number of carbon atoms?
(C1) = meth (C2) = eth (C3) = prop (C4) = but (C5) = pent (C6) = hex (C7) = hept (C8) = oct (C9) = non (C10)=dec
How are alkanes named?
identify longest chain
identify name + location of side chains
input grammar
What are the main physical properties of alkanes?
At RTP, straight chain alkanes with:
- c1-4 are gases,
- c5- 17 are liquids,
- c17-etc are solids.
Alkanes are soluble in non polar solvents not aqueous solutions
Alkanes are the least dense of all organic molecules
When does BP increase with alkanes and why?
with increasing number of carbon atoms
due to weaker intermolecular bonds
What effect does branching of alkanes have on BP?
dramatic decrease in BP
What occurs during complete combustion and what is required for it?
Complete combustion occurs when a hydrocarbon is converted to CO2 and H2O.
This requires excess oxygen.
Which halogens take part in alkane radical substitution?
Fluorine, Chlorine and Bromine
What are the steps in radical substitution of alkanes?
Nucleophile attacks electron deficient carbon at C-X bond
Nucleophile donates 2 electrons to form new dative covalent bond
C-X bond breaks heterolytically forming a halide ion (leaving group)
What alters the stability of a free radical produced during the radical substitution process?
The ability of the compounds to stabilise an unpaired electron.
The stability order is tertiary compound > secondary compound > primary compound.
What is ring strain and what does it cause?
Cyclic alkanes are strained compounds.
Ring strain results from bending of bond angles in greater amounts than normal.
This strain causes cyclic compounds of 3 or 4 carbons to be unstable so not found often in nature. (Usual angle is 109.5°)
What are carbon bond angels in cyclopropane, cyclobutane and cyclopentane?
60° in cyclopropane,
90° in cyclobutane,
108° in cyclopentane.
What is ESR?
Electron shell repulsion
Molecules and atoms are always trying to minimise this.
