4.1 Basic concepts and hydrocarbons Flashcards
homologous series definition
series of organic compounds having the same functional group, with each successive member differing by CH2
functional group definition
group of atoms responsible for the characteristic reactions of a compound
alkyl group definition
of formula CnH2n+1
aliphatic definition
compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
alicyclic definition
aliphatic compound arranged in non-aromatic rings with(out) side chains
aromatic definition
compound containing a benzene ring
benzene ring definition
functional group where carbon atoms are bounded to each other by alternating single and double bonds
saturated definition
containing only single bonds
unsaturated definition
containing multiple carbon-carbon bonds and aromatic rings
structural isomers definition
another compound with the same molecular formula but with different bonds between them
general formula definition
simplest algebraic formula of a member of a homologous series
e.g. CnH2n+2
structural formula definition
minimal detail showing arrangement of atoms in a molecule
displayed formula definition
relative position of atoms and the bonds between them
skeletal formula definition
simplified organic formula
shown by removing hydrogen atoms from alkyl chains
just carbon skeleton and associated functional group
structural isomer definition
compounds with same molecular formula but different structural formulae
types of covalent bond fission
heterolytic fission
homolytic fission
heterolytic fission definition
one bonding atom receives both electrons from bonded pair
forms cations and anions
homolytic fission definition
each bonding atom receives one electron from bonded pair
forms 2 radicals
radical definition
species with an unpaired electron
“curly arrow” uses
movement of an electron pair
shows heterolytic fission or formation of covalent bond
alkane definition
saturated hydrocarbon
contains single C-C bonds and C-H bonds as sigma bonds
free rotation of sigma bond
reaction mechanism definition
how a reaction takes place
addition reaction definition
two reactants join together to form one product
substitution reaction definition
atom or group of atoms is replaced by a different atom or group of atoms
elimination reaction definition
removal of a small molecule from a larger one
effect of chain length on boiling point
longer chain length = larger surface area = more surface contact possible between molecules = greater London forces = more energy required to overcome forced
effect of branching on boiling point
more branches = less surface points of contact between molecules = fewer London forces
also branches get in the way and prevent molecules from getting closer together as straight chain molecules
why alkanes don’t react with most common reagents
C-C and C-H sigma bonds are strong
C-C bonds are non-polar
electronegativity of C and H are very similar (can be considered non-polar)
complete combustion of alkane
alkane + oxygen -> carbon dioxide + water
incomplete combustion of alkanes
alkane + oxygen -> carbon monoxide + water + carbon particulates
reaction of alkanes and halogens
alkane + halogen -> haloalkane + hydrogen halide
only in the presence of sunlight
radical substitution definition
substitution reaction involving free radicals as a reactive intermediate
alkane substituion method
initiation -homolytic fission of halogen molecules form radicals (1 step)
propagation - radicals attack alkane (2 steps)
termination - two radicals combine to form molecule and reaction end (3 steps)
limitation of radical substitution
many products formed
have to separate desired product from everything else
alkene definition
unsaturated hydrocarbon
contains double bond
how double bond prevents rotation of carbon atoms
contains sigma bonds (direct overlap of orbitals directly between bonding atoms)
contains pi-bonds (sideways overlap of adjacent p-orbitals above and below bonding atoms)
pi-bond restricts rotation and locks bonding atoms in place
shape around double bond
trigonal planar
three regions of electron density
repeal each other as much as possible
no lone pairs
stereoisomer definition
same structural formula, different arrangement of atoms in space
why stereoisomerism occurs
rotation restricted around double bond
groups attached to each carbon atom fixed relative to each other
cis-trans isomerism requirements
has double bond
each carbon in double bond attached to two different groups (one must be hydrogen on each carbon)
E/Z isomerism requirements
C=C double bond
different groups attached to each carbon atom of C=C bond
how to predict E/Z isomerism
higher atomic number of group = higher priority
highest priority groups on same side = Z
highest priority groups on opposite sides = E
Cahn-Ingold-Prelog (CIP) rules
bond enthalpies in C=C
sigma bond = 347 kJ mol^-1
pi bond = 265 kJ mol^-1
why alkenes are more reactive than alkanes
double bond made up of sigma bond and pi bond
pi bond’s electrons more exposed (on outside of double bond) so breaks more readily
hydrogenation of alkenes
alkene + hydrogen -> alkane
requires nickel catalyst
423 K
halogenation of alkenes
alkene + halogen -> haloalkane
room temperature
used as test for unsaturation
hydration of alkenes
alkene + steam -> alcohol
requires phosphoric acid catalyst
2 possible products if unsymmetrical alkene (use Markownikoff)
addition reaction of alkenes with hydrogen halides
alkene + hydrogen halide -> haloalkane
room temperature
2 possible products if unsymmetrical alkene (use Markownikoff)
electrophilic addition
addition reactions that form saturated compounds
electrophile definition
(group of) atom(s) attracted to electron rich-centre
accepts electron pair
usually positive ion or has partial positive charge
mechanism of reaction between but-2-ene and hydrogen bromide
hydrogen bromide polar molecule as bromide more electronegative
electron pair in pi bond attracted to partially positive hydrogen atom (breaks double bond)
bond forms between hydrogen atom and carbon atom (forms carbocation)
H-Br bond breaks (heterolytic fission) and forms bromide anion
bromide anion reacts with carbocation (opposite charges), forms addition product
mechanism of reaction between propene and bromine
bromine approaches alkene
pi bond electrons causes induced dipole in bromine
pi bond electrons attracted to partial positive end of bromine (breaks double bond)
bond formed between carbon atom of double bond and bromine atom (forms carbocation)
Br-Br bond breaks (heterolytic fission), forming bromide anion
carbocation reacts with bromide anion (oppositely charged) to form addition product
Markownikoff’s rule
in a hydrogen halide + alkene reaction, most stable carbocation (the one with the most alkyl groups attached) will be formed for the halide ion to bond to
carbocation stability
more alkyl groups (R) = more stable
alkyl groups push electrons towards positively-charged carbocation
positive charge is spread out between alkyl groups, making ion more stable
repeat unit of polymer
double bond opens up
square brackets
put “n” at bottom left of right bracket (shows large number of repeats)
environmental concerns of waste polymers
polymers more readily available, cheap to purchase and convenient than better alternatives e.g. glass bottles
not very reactive, non-biodegradable so stays and impacts environment (wildlife)
recycling benefits
conserves finite fossil fuels
decreases waste going to landfill
why polymers have to be sorted
mixed polymers renders product useless (different properties)
why PVC hard to recycle
high chlorine content and additives
when burnt, hydrogen chloride (corrosive) and toxic dioxins produced
how PVC is recycled
solvents dissolves polymer, high-grade PVC recovered by precipitation from solvent, solvent used again
PVC grinded and reused to manufacture new products
why polymers can be used as fuel
derived from fossil fuels
have high stored energy value
fossil fuels incinerated, generating steam to drive a turbine producing electricity
feedstock recycling definition
chemical and thermal processes that reclaim monomers, gases or oil from waste polymers
product similar to ones produced from crude oil refineries
able to handle unsourced and unwashed polymers
biodegradable polymers
broken down by microorganisms into water, carbon dioxide, biological compounds
made from starch or cellulose
monomer
molecule that can be bonded to other identical molecules to form a polymer
compostable polymers
degrade and leave no visible or toxic residues
photodegradable polymers
contain bonds that are weakened by absorbing light to start the degradation
