chapter 13 (alkenes) Flashcards
alkenes are unsaturated hydrocarbons, what does that mean
they have at least one C=C double bond
the general formula of alkenes
CnH2n
sigma bond
overlap of atomic orbitals directly between bonding atoms
pie bond
sideways overlap of p orbitals above and below the C-C bond sigma bond
how many bonds are used in the formation of sigma bonds
three
how many pie and sigma bonds does a C=C double bond have
1 sigma and 1 pie
does the pie bond permit rotation about the C=C double bond
no, it restricts it
stereoisomers
they have the same structural formula AND molecular formula but different arrangements of atoms in 3D space
name the two different forms of stereoisomerism
E/Z isomerism
optical isomerism
requirements for E/Z isomerism to occur
the presence of a carbon to carbon double bond
two different groups should be attached to each of the carbons in the double bond
in E/Z isomerism the atoms attached to the carbons of the double bond are given priority based on…
their atomic number
z isomer
an isomer where the groups of higher priority are on the same side of the double bond
z isomer
an isomer where the groups of higher priority are on the same side of the double bond
e isomer
an isomer where the groups of higher priority are diagonally placed across the double bond
requirements for a cis-trans isomerism to occur
there should be a C=C double bond
two different groups should be attached to each carbon of the double bond
one of the attached groups on each carbon must be the same
cis isomer
trans isomer
for cis isomerism, identical groups are on the same side of the C=C double bond
in trans isomerism, identical groups are placed diagonally on the C=C double bond
why are alkenes more reactive than alkanes
because the pie electrons of the double bond are more exposed than the sigma bonds as they are outside of the double bond.
so the pie bonds break readily and alkenes undergo reactions relatively easily
addition reaction
when two reactants join together to form one product
name four addition reactions that alkenes may undergo
halogenation reactions
hydrogenation reactions
reaction with hydrogen halides
hydration reactions
what happens in hydrogenation reactions of alkenes
catalyst required for such reactions to take place
alkene reacts with hydrogen to form an alkane
a nickel catalyst
what happens in halogenation reactions of alkenes
alkene reacts with a halogen to form a dihaloalkane
test for the presence of a C=C double bond in an alkene
add bromine water dropwise
if a C=C bond is present, the bromine water decolorises from orange
what happens in the reaction of alkenes with hydrogen halides
alkenes react with hydrogen halides to form a haloalkane
if the alkene is unsymmetrical in it’s reaction with hydrogen halides, then how many possible products are formed
2
what happens in the hydration reaction of alkenes
what catalyst is required in the reaction
alkenes react with steam to form alcohol
a phosphoric acid catalyst
if the alkene is unsymmetrical in a hydration reaction, then how many possible products are formed
2
which has a higher bond enthalpy between a sigma and a pie bond, and what does this indicate
a sigma bond has a higher bond enthalpy than a pie bond and this shows that a pie bond is weaker than a sigma bond. it breaks more readily
electrophile
an electron acceptor
in the electrophilic addition of alkenes to hydrogen halides, what causes the double bond in the alkene to break
the attraction between the partially positive hydrogen atom in the hydrogen halide and the electron pair in the pie bond
in electrophilic addition of alkenes, the electrophile breaks by
heterolytic fission
the major product is formed via the…………….
most stable carbocation intermediate
the two ways that we determine the stability of a carbocation intermediate
the more alkyl groups attached to the carbocation intermediate, the more stable it is
or
the fewer hydrogen atoms attached to the carbocation intermediate, the more stable it is
polymer
consists of many monomers joined together to make a long chain
benefits for sustainability of processing waste polymers
waste polymers can be used as fuel by incinerating them to produce heat, which in turn generates heat to power turbines to produce electricity
feedstock recycling: reclaiming monomers from waste polymers which can be used as raw materials for the production of new polymers
recycling
PVC recycling
environmental benefits of developing biodegradable and photodegradable polymers
bioplastics are made from plant-based materials, so they are renewable and sustainable
biodegradable polymers
polymers that are broken down by bacteria into water, carbon dioxide and biological compounds
photodegradable polymers
polymers that contain bonds which are weakened by absorbing light
