Alkenes Flashcards
describe alkenes homologous series
Homologous series of unsaturated hydrocarbons with general formula CnH2n
angles found in alkenes
C=C are planar (120°)
CH3 are tetrahedral (109.5°)
reactivity compared to alkanes and reason pls
More reactive than alkanes due to high electron density (two pairs of electrons)
unsaturated meaning
contains at least one double bond, a centre of high electron density
what type of mechanism for alkenes and why
Electrophilic addition
Occurs due to high electron density so can easily be attacked by electrophiles
electrophile
an electron pair acceptor – needs positive charge e.g. protons, acids (H+)
addition reaction
reaction where two molecules produce one molecule
carbocation
positively charged carbon atom
test for unsaturation
use bromine water if alkene it will turn orange -> colourless
reagent of reaction from alkene into dibromoalkane
bromine (Br2)
conditions for reaction from alkene into dibromoalkane
room temperature, aq
what does alkene and bromine make
dibromoalkene
stages of reaction from alkene -> alcohol
reagent, conditions
- reaction with sulphuric acid
alkene -> alkyl hydrogensulphate
c. H2SO4
room temperature, aq - reaction with wayer (hydrolysis)
alkyl hydrogensulphate -> alcohol
water
warm
what does H2SO4 act as when making an alcohol form alkene
catalyst because it is regenerated at the end
reaction from alkene to bromoalkane reagent and conditions
HBr (for chloroalkane HCl)
room temperature, aq
Markovnikov’s rule
bromine will be added to the carbon with the fewest hydrogens on it as it is the most stable carbocation intermediate to form major product
why could more than one product be produced
Alkene is asymmetrical
Draw out carbocations and identify as primary, secondary and tertiary
State which is the more stable carbocation e.g. secondary more stable than primary
More stable carbocation is stabilized because carbon atoms around carbocation are electron releasing so reduce the charge and stabilises it
reaction that converts ethene -> ethane
conditions (3) and use (1)
hydrogenation of ethene
conditions: nickel catalyst, H2 gas, 140°C
used for the hardening of vegetable oil to form fats in the manufacture of margarine
monomer
a small molecule that can combine with similar molecules to form a long molecule called a polymer
addition polymer
very long molecules made of smaller molecules called monomers are generally unreactive
addition polymerisation
the process where monomer join by single bonds to form 1 large polymer molecule
types of poly(ethene)
low density poly(ethene)
high density poly(ethene)
conditions and structure of low density poly(ethene)
Under high pressures and a trace of oxygen
Polymer chains have random branches so are unable to pack closely together
conditions and structure of high density poly(ethene)
Catalyst, 50°C, slightly high pressure
Polymer chains are straighter without branches so are able to pack closely together
what are biodegradable polymers
able to be broken down by microorganisms
poly(chloroethene) PVC properties and uses
Properties can be modified by a plasticiser
- hard, rigid, tensile strength becomes more flexible and softer
Uses: window frames, pipes
