module 4 - core organic chemistry Flashcards
different ways of presenting molecules
- empircal
- molecular
- displayed
- structural
- general
- skeletal
general formula of alkanes
CnH2n+2
structural formular of butane
CH3CH2CH2CH3
displayed formular of ethanol
H H
/ /
H—-C———C—O—-H
/ /
H H
skeletal formular of butan-2-ol
draw
homologus series
organic compounds that have the same functional group but each successive member differs by CH2
functional group
group of atoms responsible for characteristic reactions of a compound
example of a functional group
COOH
alkyl group general formula
CnH2n+1
aliphatic
compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
alicyclic
aliphatic compound arranged in non-aromatic rings with or without side chains
aromatic
a compound containing a benzene ring
amine displayed formula
H
/
-N
\
H
aldehyde molecular formula
-CHO
difference between saturated and unsaturated hydrocarbons
saturated - single c-c bonds only and saturated with hydrogens
unsaturated - presence of multiple c-c double bonds.
isomerism
where molecules exist with the same molecular formula, with a different structural formula
two types of isomerism
structural
stereo
3 types of structural isomers
position
functional group
chain
how are covalent bonds broken
homolytic fission
heterolytic fission
homolytic fission
bond splits equally - free radicals formed
heterolytic fission
atom receives both electrons from bonding pair
radical
species with unpaired electron
curly arrow represents…
movement of electron pair, showing either heterolytic fission or formation of a covalent bond
why does the boiling point of alkanes increase as the molecule gets bigger
- more electrons
- stronger london forces which require more energy to break
what are alkanes
- saturated hydrocarbons containing single c-c and c-h bonds as σ bonds
what are σ bonds
end on end overlap of the sp2 orbital
bond angle of alkanes
109.5
shape of alkanes
tetrahedral shape
which alkane has a higher boiling point : straight chain or branched
- straight chain alkanes have higher boiling points than branched alkanes
- molecules can get closer making more points of contact for london forces to occur, so more energy is required to break these forces
why are reactions of alkanes limited
due to lack of polarity of alkane σ bonds
what reactions do alkanes go under
combustion reactions
free radical substitution
reactivity of alkanes
- relatively unreactive
- non polar
- very low polarity of σ bonds present
uses of alkanes
fuels - readily available, easy to transport, burns to release no toxic products
incomplete combustion of alkanes can produce …
carbon monoxide
dangers of carbon monoxide
- colourless, odourless + highly toxic.
- binds irreversibly with haemoglobin in rbc to form carboxyhaemoglobin preventing oxygen passing round body.
three steps of free radical substitution
initiation
propagation
termination
what are the only two reactants that can react together in a free radical substitution
a halogen atom and an alkane
reaction of chlorine with methane
full reaction:
CH4(g) + Cl2(g) -> CH3Cl(g) + HCl(g)
initiation:
Cl2 —> (UV) 2Cl*
propagation:
CH4 + Cl* -> CH3* + HCl
CH3* + Cl2 -> CH3Cl + Cl*
termination:
2Cl-> Cl2
2CH3 -> C2H6
Cl + CH3* -> CH3Cl
reaction of bromine with methane
full reaction:
CH4(g) + Br2(g) -> CH3Br(g) + HBr(g)
initiation:
Br2 —> (UV) 2Br*
propagation:
CH4 + Br* -> CH3* + HBr
CH3* + Br2 -> CH3Br + Br*
termination:
2Br-> Br2
2CH3 -> C2H6
Br+ CH3* -> CH3Br
limitations of free radical substitutions
- collisions are uncontrollable so can’t make one particular product
- further substitutions can happen
- if unwanted product is made, expensive separation will be required
- reactions at different positions in a carbon chain
what are alkenes
- unsaturated hydrocarbons containing c-c double bonds
- double bond comprised of a σ bond and π bond
what is a π bond
- sideways overlap of p orbitals
longer chain alkenes =
less volatile than shorter chain cause there’s more electrons, more and stronger london forces, requiring more energy to break
more branched alkenes =
more volatile than less branched - can’t pack closely, less points of contact, less london forces, requires less energy to break
explanation of shape of alkenes
trigonal planar shape 120
- three bonding pair of electrons are in plane of molecule and repel each other (electron pair repulsion)
- The fourth π bonding pair forms double bond in combination with carbon-carbon σ bond
stereoisomerism
compounds with the same structural formula but with a different spatial arrangements
presence of a double bond can create two possible structures. what are they
cis structure
trans structure
how does E/Z isomerism occur
- if the C=C double bond is quite rigid and prevents freedom of rotation
- 2 different atoms or groups on each carbon atom of the double bond
when is E/Z naming applied
when there are 3/4 different substituents
difference between E/Z isomerism and cis/trans isomerism
cis/trans isomerism is used when the groups attached to both the carbons are the same
E/Z isomerism is used when there is 3 or 4 different groups are attached to each carbon
what is the name of the rule used to identify E/Z stereoisomers
cahn-ingold-prelog (cip)
cip rules
- atom with the higher atomic number has the higher priority
- if atoms or groups are the same, next point of connection is considered
name of mechanism in which alkenes react
electrophilic addition
reactivity of alkenes in terms of relatively low bond enthalpy of π bond
- π bond occurs above and below the two nuclei so weaker attraction
- the π electrons are more exposed than the σ bond so they’re more prone to electrophilic attack
4 addition reactions of alkenes
hydrogenation
halogenation
hydrohalogenation
hydration
addition reaction of hydrogen in presence of a suitable catalyst
hydrogenation:
- H2 and Ni catalyst necessary
- 150°C
- alkene -> alkane
addition reaction of halogens to form dihaloalkanes, including qualitative test
halogenation:
- add bromine water to sample
- presence of alkene = orange -> colourless
addition reaction of hydrogen halides to form haloalkanes
hydrohalogenation:
-HX has a permanent dipole
- Hδ⁺ is the electrophile
- Pair of e⁻s attracted from π bond
- Heterolytic fission of H-X bond
- Carbocation formed (C⁺)
- X⁻ now a nucleophile
- single halogen atom added to the molecule
addition reaction of steam in the presence of an acid catalyst
hydration:
- h2o , 300°C
- H3PO4 (catalyst)
- alkene -> alcohol
- industrial prep of alcohol
product of hydrogenation
alkene -> alkane
product of halogenation
dihaloalkane
product of hydration
alcohol
electrophile
electron pair acceptor
- an atom or group of atoms that is attracted to an electron-rich centre and accepts an electron pair
- usually positive ion or contains atom with partial positive charge (δ⁺)
electrophilic addition in alkenes by heterolytic
hx has a permanent dipole
- hδ⁺ is the electrophile
- pair of e⁻s attracted from π bond
- heterolytic fission of H-X bond
- carbocation formed (C⁺)
- x⁻ now a nucleophile
- single halogen atom added to the molecule
rule that predicts formation of a major organic product
markovnikov’s rule
markovnikov’s rule
- halide ion will always add to most stable carbocation
- number of carbon atoms attached to carbocation decides stability
more carbons attached to carbocation =
more stable
conditions needed for polymerisation
high pressure, heat and a catalyst
benefits and limitations of sustainability of processing waste polymers by combustion for energy production
- combustion removes the polymers and can generate power as an additional benefit - thereby saving fossil fuels.
- toxic products of some polymers and polymers that contain chlorine would create HCl as a waste gas which contributes to acid rain
- this process still causes environmental pollution as carbon within polymer can be released as carbon dioxide contributing to global warming
benefits of sustainability of processing waste polymers by use as organic feedstock for production of plastics
- chemical feed-stock recycling breaks down polymers without separating them = forms simple gases that can then be used to manufacture pure, fresh polymers
- waste polymers broken down, by chemical and thermal processes, into monomers, gases and oils
- products are then used as raw materials in production of new polymers and other organic chemicals
limitations of sustainability of processing waste polymers by removal of toxic waste products
- use of landfill sites = not ideal
