15 - hydrocarbons Flashcards
alkanes
saturated hydrocarbons with the general formula CnH2n+2
saturated hydrocarbons
compound of hydrogen and carbon only in which the C-C bonds are all single covalent bonds, resulting in the maximum number of hydrogen atoms in the molecule
why are alkanes generally unreactive
small electronegativity difference between C and H (almost equal electron sharing)
are alkanes polar or non polar
non polar
what attracts nucleophiles
no partial positive charges on carbon atoms
what attracts electrophiles
areas of high electron density
alkane reactions
. combustion
. substitution by halogens in sunlight
non polar compounds don’t react with polar compounds
they are immiscible
alkane combustion (complete)
alkane + oxygen => carbon dioxide + water
alkane incomplete combustion (when petrol/diesel mixed with air)
alkane + oxygen => carbon monoxide + water
carbon monoxide
. toxic gas
. bonds with haemoglobin in blood
. oxygen can’t bond and can’t be transported
. odourless
road traffic releases what gases?
. carbon monoxide
. acidic nitrogen oxide (contribute to acid rain which kills life and corrodes buildings)
. unburnt hydrocarbons/ VOCs
catalytic converters
. oxidation of carbon monoxide
. reduction of nitrogen oxides
. oxidation of unburnt hydrocarbons
DON’T REDUCE CO2
2CO + 2NO => 2CO2 + N2
2CO + O2 => 2CO2
alkane substitution reaction
alkane + halogen => haloalkane + HCl
INITIATION STEP
Cl2 => UV light => 2Cl
PROPAGATION STEP
CH3CH3 + Cl. => .CH2CH3 + HCl
.CH2CH3 + Cl2 => CH3CH2Cl + Cl.
TERMINATION STEP
2 free radicals reaction, eg
.CH2CH3 + .Cl => ClCH2CH3
.CH2CH3 + .CH2CH3 => CH3CH2CH2CH3
unsaturated hydrocarbons
compounds of hydrogen and carbon only whose molecules contain carbon to carbon double/triple bonds
cracking
the process in which large, less useful hydrocarbon molecules are broken down into smaller, more useful molecules in an oil refinery
lighter factions of crude oil are in
higher demand
ways to make alkenes
. catalytic cracking
. elimination of a hydrogen halide from a halogenoalkane by heating with ethanolic sodium hydroxide
. deydration of an alcohol by using. heated catalyst or concentrated acid
what is dehydration
elimination of a water molecule from a reactant molecules
addition reactions of the alkanes
. hydrogenation (addition of alkenes with hydrogen)
. addition of hydrogen halides
. addition of halogens
. addition of steam (high temp, high pressure, H3PO4 catalyst)
intermediate
a species, such a a a carbocation, which is formed at a particular step of the reaction.
stable enough to react with another substance, but not stable enough to be a product
often a have a partial postive / negative
bromine test
bromine water decolorises if compound is unsaturated
unsaturation test (not br)
alkene + KMnO4 cold => diol
purple to colourless
powerful oxidsing agent
KMnO4
