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The functional group contains a double covalent bond which is a
region of high electron density
The sheep around each carbon atom in the carbon carbon double bond is
trigonal planar bond angle 120°
pi bond
forms when p orbitals overlap
presence of a pi bond means there is
restricted rotation about the CC bond
two two or three carbon carbon bonds
diene, triene
Why does EZ isomerism occur
as a result of restricted rotation about the trigonal planar carbon carbon double pond
for an alkene to exhibit EZ isomerism
each carbon atom of the carbon carbon double bond must be bonded to different groups
to be the z isomer
both highest priority groups should be on the same side of the CC bond
highest priority
the atom with the highest atomic number
are alkenes reactive or unreactive and why
they are reactive due to the high electron density of the CC double bond
What kind of reactions do alkenes undergo in which a small molecule is added across the CC group to form a saturated molecule
addition reactions
electrophile
electron pair acceptor
Why do alkenes react with electrophiles
electrophiles are attracted to the high electron density in the carbon carbon double bond
What happens during the reaction
covalent bonds are both broken and formed producing a reactive positively charged intermediate called a carbocation
What is a mechanism
shows the breaking and forming of covalent bonds using curly arrows
curly arrows must be drawn accurately and start from either
a lone pair or a covalent bond
reagent of reaction of alkenes in halogens
X2
conditions
room temp
What is the electrophile in this reaction
the bromine molecule
What does the high electron density do to the BR2 molecule
it induces a dipole
how does the BRBr bondn break
by heterolytic fission
bromine is used
to test the presence of a CC group: orange to colourless
electrophilic addition of concentrated sulphuric acid to alkenes reagent and conditions
reagent: concentrated sulphuric acid
conditions: room temp
What does a sulphuric acid molecule look like
A person cheering
how do organic hydrogens sulfates form an alcohol
they are readily hydrolyzed with warm water
how can alcohols be prepared from alkenes
hydration of alkenes with steam in the presence of a phosphoric acid catalyst
primary carbocation
A carbocation which has one carbon atom directly bonded to the positively charged carbon. only one alkyl group
secondary carbocation
A carbocation which has two carbon atoms directly bonded to the positively charged carbon.
tertiary carbocation
A carbocation which has three carbon atoms directly bonded to the positively charged carbon.
Which is the most stable carbocation
tertiary
Which is the least stable carbocation
primary
positive inductive effect
The tendency of alkyl groups to release electrons which help to stableize the positive charge of carbocation
addition to an unsymmetrical alkene produces
two different organic products, the major product and the minor product
yield of a particular product is related to
stability of carbo cation formed from
explanation for why something is a major product
X is the major product - formed via a secondary carbocation. 2° carbocations have two alkyl groups. 1° carbo cations have only one alkyl group. 2 alkyl groups release more electrons and 2° carbo cations :. The more stable than 1°
when how hydrogen is added across a C=C bond a what is produced
an alkane
hydrogenation of alkanes is important because
it's an important industrial process for example margarine is produced by the hydrogenation of long chain fats or oils which contain CC double ones
how are polymers formed
when many is small molecules called monomers join together to form a very large molecule
alkenes act as monomers in
polymerization reactions- CC double bond breaks allowing monomers to add together
repeating unit
specific arrangement of atoms that occurs in the structure over and over again
polypropylene use
food containers
polyprop 2 enenitrile use
synthetic fibres which are used in blankets, rugs and clothing
polytetrafluoroethene use
Teflon - non-stick pans
polyphenylethene use (polystyrene)
low density so used for packaging
poly 1,1 dichlorothene use
shower curtains, plastic films
properties of poly alkenes
unreactive due to the backbone of single CC bonds so saturated
properties of poly alkenes depend on
the structure and the intermolecular forces between neighbouring polymer chains
polyethylene has
van der Waals between neighbouring chains
The properties of polymers like poly ethylene can be modified by
increasing branching
What is the effect of this
it decreases points of contact so the van der Waals forces are weakened which causes increased flexibility and a lower melting point
polychloroethane properties
rigid and brittle. contains polar CCL bonds therefore has permanent dipole dipole forces between polymer chains.
plasticisers
make polymer more flexible as they force neighbouring chains apart allowing them to slide over each other. get in between neighbouring chains and reduce intermolecular forces.
