organic chem - alkanes and alkenes Flashcards
3 steps of bromination
- initiation
- propagation
- termination
explain first step of bromination
- initiation - UV light sets off reaction by splitting apart the Br2 molecules, creating 2 Br radicals
explain third step of bromination
- termination - 2 radicals come together and give pairing of electrons, becoming stable
disadvantages of bromination by a means of producing bromoalkanes
- cant control products made
- cant control isomers made
explain second step of bromination
- propagation - chain reactions - Br radical reacts with C-H bond in methane, forming methyl radical and HBr
- methyl radical reacts with Br2 making bromomethane and Br radical
unbranched alkane molecules get bigger - bp?
increase - as attraction increase (London forces increase)
branched alkane molecules get bigger - bp?
decrease - as branches mean molecules cant get close to each other - attraction is less, intermolecular forces are weaker (London forces decrease)
Z isomer
same side of double bond
E isomer
different side of double bond
sis isomer
same side of double bond
trans isomer
different side of double bond
when do you use sis-trans isomerism?
if other group on the carbon is a hydrogen
stereoisomer
atoms in the isomer are in the same order but have different arrangements in space
how do E/Z and cis/trans isomers arise?
restricted movement around C=C bond
when there are different elements around the c=c, which do you take?
highest priority from each side (highest atomic number)
ester functional group
-COOC
aldehyde functional group
-CHO
ketone functional group
C(CO)C
aliphatic
carbons joined In unbranched, straight chains OR branched chains OR non-aromatic rings
aromatic
some or all of carbons found in a benzene ring
alicyclic
carbon atoms joined in a ring (cyclic structures with/without branching)
alkynes
at least 1 C=C bond
amino functional group
NH3
nitrile functional group
CN (triple bond)
empirical formula
simplest ratio of the atoms of each element in a compound
molecular formula
number and type of atoms in each compound
general formula
simplest algebraic formula for the homologous series (eg. CnH2n)
displayed formula
shows relative positions of atoms in a molecule and the bonds between them
structural formula
shows arrangement of atoms in a molecule
skeletal formula
simplified organic formula - removing all C and H atoms and bonds to H atoms
homolytic fission
bond breaks and each atom takes 1 of the electrons from the shared pair
ways of breaking a covalent bond
- homolytic fission
- heterolytic fission
heterolytic fission
bond breaks and one of the atoms take both electrons from the shared pair
conditions for reaction of alkanes and halogens
sunlight - uv radiations provides activation energy
why are alkenes more reactive then alkanes
C=C allows addition reactions to take place much more easily as π bond breaks more easily then σ bond (only bond in alkanes)
bonds in alkenes
σ and π
reaction of alkene -> alkane
HYDROGENATION
conditions for hydrogenation
423K, nickel catalyst - alkene reacted with hydrogen
reaction of alkene -> haloalkane (eq. + conditions)
alkene + gaseous hydrogen halide –(room temp)–> haloalkane
reaction of alkene -> alcohol
HYDRATION
conditions for hydration
alkene + steam –> alcohol
phosphoric acid catalyst
products of oxidisation of primary alcohols
aldehydes -> carboxylic acids
products of oxidisation of secondary alcohols
ketones
why are alcohols soluble
polar molecules due to difference in electronegativity between O and H
boiling point trend down group of haloalkanes
increase - as van Der Waals forces increase in strength due to no. of electrons
solubility of haloalkanes
dissolve in alcohol but not in water
why is the carbon-halogen bond generally polar?
halogen is much more electronegative
nucleophile
a species that DONATES an electron pair to form a chemical bond
pattern as go down group 7 of speed of hydrolysis
increase, as weaker chemical bonds are easier to break
useful properties of CFCs (3)
- stable
- non-flammable
- non-toxic
uses of CFCs
- aerosols
- fridges
- aircon
how do CFCs break down ozone
catalyse the reaction
overall equation of ozone breakdown by CFCs
O3 + O –> 2O2
species responsible for ozone destruction (not CFCs)
Nitrogen oxides
dehydration reaction - example
alcohol –> alkene
hydration reaction - example
alkene –> alcohol
alcohol –> haloalkane reaction - type of reaction
substitution
haloalkane –> alcohol (type of reaction)
hydrolysis
alkene –> haloalkane - type of reaction
electrophilic addition
alcohol –> ketone
oxidation
alcohol –> aldehyde
oxidation
aldehyde –> carboxylic acid
oxidation
alcohol –> carboxylic acid
oxidation
alkene –> dihaloalkane
electrophilic addition
alkane –> haloalkane - type of reaction
free radical substitution
alkene –> alkane
hydrogenation
conditions for hydration
H3PO4 catalyst
300 degrees C
60-70 atm
dehydration conditions
conc. H2SO4
oxidation conditions
K2Cr2O7
H2SO4
heat
alcohol –> haloalkane (substitution) conditions
sodium halide
H2SO4
REFLUX
requirement for H-bonding
must have a H bonded to either O, F or N
London forces
instantaneous dipoles - electrons concentrated on one side of molecule, induces dipoles in neighbouring molecules
dipole-dipole forces
between sigma + and sigma -
compared to alkanes, alcohols are…
less volatile
higher melting points
greater water solubility
why are alcohols less volatile then alkanes
permanent dipole means more attractions between molecules ∴ more energy required to overcome
bonding in alkanes
sigma (σ) - single bonds
saturated hydrocarbon
shape of alkanes
each c atom surrounded by 4 σ bonds - repulsion creates tetrahedral arrangement and bond angle approx 109.5
conditions required for E/Z isomerism
- C=C bond
- different groups on each of the Cs of bond
conditions required for cis-trans isomerism
- same as E/Z
BUT must have H as one of bonded groups
products of unsymmetrical alkene reaction
major + minor
markownikoff’s rule
when unsymmetrical alkene reacts with hydrogen halide, the H of hydrogen halide attaches itself to the atom with most number of H’s bound to it and least number of C’s
why is the major product more stable
more alkyl groups attached
positive electron inductive effect, spreading charge out making carbocation more stable
bioplastics
produced from plant starch
structural isotope
same molecular formula but different structural formula
why are alkanes unreactive
- high enthalpy and low polarity of σ bond
why are alkenes reactive
low bond enthalpy of π bond
as you go down halogens, reactivity of nucleophilic sub of haloalkanes…
- why?
increases - reaction rate increases
- bonds get weaker + break more easily
greater atomic radius, more sheilding, weaker attraction, weaker bonds more easily broken
3 ways chemists can make polymer disposal more environmentally friendly
- make photodegradable polymers
- make biodegradable polymers
- develop ways of sorting AND recycling polymers
2 main ways of making ethanol
+ equations
- fermentation of yeast
C6H12O6 + H2O -> 2C2H5OH + 2CO2 - hydration of ethene
C2H2 + H2O -> C2H5OH
why are there still concerns about ozone depletion
- long residence time of CFCs
- (not just CFCs) - other ozone depleting substances
bond angle and type of molecule in alkenes
planar
120
restricted movement?
atoms attached to the carbons cannot change place
3 methods ensuring polymers are used sustainably
- explain
- combustion - burnt to produce energy
- toxic products - combustion can produce toxic products (HCl) removed and safely disposed of
- feedstock recycling - broken down into monomers to produce new polymers
hydrolysis of haloalkane?
when halogen is replaced by OH group = alcohol
radical
atom/molecule with single unpaired electron
why are alkanes not very reactive
- low bond polarity of sigma bond
- high enthalpy of “”
