Module 4 - Chapters 11-13 P2 Flashcards
what are organic compounds?
Any compounds containing carbon
saturated hydrocarbons
single carbon-carbon bonds only (more saturated with hydrogen)
unsaturated hydrocarbons
one or more carbon-carbon double or triple bonds (less saturated with hydrogen)
compound with a triple bond
alkyne
general formula of alkane
CnH2n+2
general formula of alkyl
CnH2n+1
general formula of alkene
CnH2n
general formula of alcohol
CnH2n+1 OH
general formula of carboxylic acids
CnH2n O2
general formula of ketones
CnH2nO
definition of homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH2
Functional group
part of the molecule largely responsible for the molecule’s chemical properties
what functional group does an amine group have?
NH2
name three classifications of hydrocarbons
aliphatic, alicyclic and aroMATic (not aroMANtic)
aliphatic hydrocarbons
carbon atoms arranged in chains (branched or unbranched)
alicyclic hydrocarbons
carbon atoms joined in a ring (cyclic) structure (branched or unbranched)
aromatic hydrocarbons
some or all of the carbon atoms are found in a benzene ring (C6H6)
general formula of alkyne
CnH2n-2
general formula of cycloalkane
CnH2n
prefix for naming carbon chain with 12 carbon atoms
Dodec
prefix for naming carbon chain with 20 carbon atoms
Eicos
functional group of aldehyde
CHO (O double bonded to C), functional group is always on carbon 1 for aldehydes
suffix (ending) for aldehydes
-al
functional group for ketones
C(CO)C (chain of 3 carbons and O double bonded to middle one)
suffix (ending) for ketones
-one
functional group for carboxylic acids
COOH (one O double bonded to C and one bonded as part of OH to carbon)
suffix (ending) for carboxylic acids
-oic acid
functional group for esters
COOC (one O double bonded to C, other O single bonded to two Cs)
suffix (ending) for esters
-oate
functional group for acyl chloride
COCl (O double bonded to C)
suffix (ending) for acyl chlorides
-oyl chloride
suffix (ending) for amines
-amine
functional group for nitriles
CN (N triple bonded to C)
suffix (ending) for nitriles
nitrile
molecular formula
shows the number and type of atoms of each element present in a molecule, doesn’t show the bonding
definition for empirical formula
the simplest whole-number ratio of the atoms of each element present in a compound
displayed formula
shows the relative positioning of all of the atoms in a molecule and the bonds between them, each line represents a pair of shared electrons
structural formula
shows the arrangement of the atoms in a molecule by showing clearly which groups are bonded together
skeletal formula
a simplified organic formula with all of the carbon and hydrogen labels removed along with any bonds to hydrogen atoms, this just leaves a carbon skeleton and any functional groups
definition of structural isomers
molecules with the same molecular formula but different structural formula
what are the three types of structural isomers?
chain, positional, functional group
chain isomerism
when the carbon atoms are moved on the original carbon chain to form structural isomers
positional isomerism
when the basic carbon skeleton remains unchanged but important groups (such as functional groups) are moved around on that skeleton
functional group isomerism
when molecules containing different functional groups have the same molecular formula, functional groups can be changed (e.g. ketones/aldehydes)
what are the components of crude oil?
petroleum gases, petrol (gasoline), kerosene (paraffin), diesel, lubricating oil, heavy fuel oil, bitumen
use of petroleum gases
used in domestic fuel
use of petrol/ gasoline
cars
use of kerosene/ paraffin
aircraft
use of diesel
cars
properties of small molecules in crude oil
low bpt, light in colour, easy to ignite, not viscous
properties of large molecules in crude oil
high bpt, dark in colour, difficult to ignite, thick/viscous if liquid (bitumen = solid at room temp)
why does increase in chain length in hydrocarbons in crude oil increase bpt?
london forces increase because more electrons are present and increasing chain length increases surface contact
why does branching of alkanes decrease bpt?
- results in decreased points of surface contact between molecules so london forces decrease.
- branching also prevents molecules packing together as easily so molecules are further away and intermolecular forces decrease
what type of covalent bond bonds each carbon in an alkane?
sigma bonds ( σ) , formed by the overlapping of orbitals with each overlapping orbital containing one electron
why is it not possible for alkanes to have stereoisomers?
the sigma bond allows free rotation of atoms around the molecule
why do alkanes have a low reactivity?
- the sigma bonds are very strong (high bond enthalpy)
- C-C bonds are non-polar
- C-H bonds are considered non-polar due to the similar electronegativity of C and H
combustion
when alkanes react with oxygen to form carbon dioxide and water, heat is also produced
why are alkanes used as fuels?
- readily available
- easy to transport
- easy to burn in a plentiful supply of oxygen without releasing toxic products
composition of natural gas
typically 80% methane with varying proportions of ethane, propane and butane
alkane which is a component of petrol
heptane
incomplete combustion
in a limited supply of oxygen, hydrogen atoms always oxidised to water but carbon may form carbon monoxide or soot (soot = singular carbon atoms)
carbon monoxide
colourless, odourless, highly toxic
what are the two types of fission to break covalent bonds?
homolytic and heterolytic fission
homolytic fission
each of the bonded atoms takes one of the shared pair of electrons from the bond, each atom becomes a radical so the products are the same
radical
has a single unpaired electron
diradical
has two unpaired electrons
heterolytic fission
one of the bonded atoms takes both of the electrons from the bond, positive and negative ions are formed so the products are different
name three types of reactions
addition, substitution, elimination
addition reaction
two reactants join together to form one product
substitution reaction
an atom or group of atoms is replaced by a different atom or group of atoms
elimination reaction
the removal of a small molecule from a larger one, one reactant molecule forms two products
photochemical reaction
alkanes react with halogens in the presence of UV light because the UV provides the initial energy for a reaction to take place
name the stages of free radical substitution
initiation, propagation, termination
initiation
a chlorine molecule is broken down into 2 free radicals by homolytic fission, a superscript dot alongside an atom shows it is a radical (no dot required for diradical)
important point to remember about initiation
the products don’t have to be the same element - just the same type of radical
propagation
chain reactions, one of the reactants and one of the products is always a free radical. always happens in two steps
propagation reactions to learn
CH4 + Cl’ = CH3’ + HCl
CH3’ + Cl2 = CH3Cl + Cl’
(continued)
CH3Cl + Cl’ = CH2Cl’ + HCl
CH2Cl’ + Cl2 = CH2Cl2 + Cl’
(or the chlorine radical in step 2 could react with methane again as in step 1)
termination
two radicals collide to form a molecule with all electrons paired, all free radicals are removed from the system
problems with free radical substitution
- further substitution can occur, may not result in the desired products
- position of substitution cannot be controlled so a mixture of mono-substituted isomers will be formed
how the products of further substitution can be controlled
using an excess of certain chemicals
why do alkenes have lower bpts than alkanes?
double bond puts a kink in the chain so the chains cannot pack together as closely (decreasing surface contact so decreasing london forces)
what is the other type of covalent bond (other than sigma) in alkenes?
pi bond, formed by the overlap of two p orbitals
why is the pi bond weaker than the sigma bond?
electrons are further from the nucleus in the pi bond
why can stereoisomers be formed with alkenes?
the pi bond restricts rotation of atoms around the molecule
key point about double bonds and drawing in 3D
only counts as one area of electron density
definition of stereoisomerism
when molecules have the same molecular and structural formulae but a different arrangement in space
types of stereoisomerism
E-Z, cis-trans
rules for E-Z isomerism
- must have a C=C double bond
- different groups must be attached to EACH CARBON atom in the double bond
Z isomers?
groups (same or with highest priority) on the same side of the molecule
E isomers?
groups (same or with highest priority) on different sides of the molecule
rules for cis-trans isomerism
- must have C=C double bond
- two different groups must be attached to EACH CARBON but one of the groups must be hydrogen
cis isomers?
hydrogen atoms on the same side of the molecule
trans isomers?
hydrogen atoms on different sides of the molecule (diagonal)
Cahn-Ingold-Prelog priority rule
priority is assigned to one of the groups on each carbon, two highest priority groups used to determine if E or Z.
- ATOMS directly attached to the double bond are assessed for priority by highest atomic number,
- if atomic numbers are the same then all atoms attached to that atom are listed from highest to lowest atomic number.
- compare the lists element by element and the list with the element with the highest atomic number is given priority
- double bonded atoms are counted twice in the list
types of addition reactions with alkenes
hydrogenation, halogenation, hydration
hydrogenation
hydrogen is added across the double bond, if enough hydrogen is present all of the double bonds are always broken. occurs with a nickel catalyst
hydrogenation of unsaturated fats forming trans double bonds
formed during the process of the pi bond breaking and reforming
unsaturated fats v saturated fats mpt
unsaturated fats have a lower mpt because they have a greater number of C=C bonds causing kinks in the chain so more difficult to pack together
hydrogenation of vegetable oils
naturally-occurring vegetable oils in the cis configuration so more difficult to pack together due to kinks in the chain. mpt increases when hydrogenated so solidify, some cis isomers become trans
halogenation
halogens added across a double bond, alkenes react with gaseous hydrogen halides to form haloalkanes
testing for alkenes/unsaturation
bromine water added across double bond, de-colourises if added across double bond so if bromine water decolourises then double bond(s) are present (the molecule is unsaturated)
hydration
alkenes react with steam to form alcohols in the presence of a phosporic acid catalyst or concentration sulfuric acid. the steam adds across the double bond, forming hydroxide groups to form an alcohol
why are alkenes more reactive than alkanes?
the pi bond is weaker than a sigma bond
what is electrophilic addition?
alkenes forming saturated compounds in addition reactions
why do electrophiles attack the double bond in alkenes?
has high electron density due to electrons in pi bond
definition of electrophiles
electron pair acceptors (usually a positive ion or slightly positive molecule)
key points to remember about drawing the reaction mechanisms in electrophilic addition
- curly arrows from the lone pair of electrons in the bond
- bond breaks by heterolytic fission in non alkene molecule (e.g. HBr)
- negative atom remaining = nucleophile
- electrophile (hydrogen) hydrolyses the double bond
- remaining carbon = carbocation (positive)
nucleophile
attacks the carbocation (have an electron pair so opposite of electrophile)
why are curly arrows used?
show movement of electrons, head of the arrow must point to where electrons will be when new bond formed
rate of reaction of electrophilic addition as you go down group 17
rate of reaction increases because atomic radius increases so strength of hydrogen-halide bond decreases. less energy required to break bond so rate of reaction increases
Markovnikoff’s rule
determines the major product (most abundant) of the two isomers formed. when a hydrogen halide reacts with an unsymmetrical (not the same on both sides) alkene the hydrogen attaches to the carbon with the greatest number of hydrogens
types of carbocations in Markovnikoff’s rule
primary, secondary, tertiary
primary carbocation
positive carbon only attached to one alkyl group (charge at end of chain)
secondary carbocation
positive carbon attached to two other alkyl groups
tertiary carbocation
positive carbon attached to three alkyl groups
why Markovnikoff’s rule works
- most stable carbocations are more abundant as products
- secondary and tertiary carbocations are more stable because the positive charge can be decreased by the electrons on the alkyl groups.
- electron-donating/ electron pushing effect
- more alkyl groups = charge more spread out
electron-donating/ electron pushing effect
alkyl groups have an electron-donating/ electron pushing effect away from them (to the carbocation) due to the other end of the bond attracting the electrons more strongly,
therefore the movement of electrons towards the positive charge decreases the charge and the charge becomes more spread out
why are more stable carbocations more abundant as products?
less activation energy is required to form more stable carbocations so most of the mechanism occurs to form the most stable carbocations
definition for activation energy
the minimum energy needed before a reaction will occur
markscheme answer for explaining the most abundant carbocation formation
“The secondary (or tertiary) carbocation formed in this reaction is more energetically stable than the primary (or secondary) one which would be formed if the addition was the other way around, and so less activation energy is needed.”
definition for polymerisation
an alkene (monomer) undergoing addition reactions with itself to form a polymer
conditions required for polymerisation
200°C, 200atm, a small amount of oxygen free radical as an initiator
definition for repeat unit
the specific arrangement of atoms in the polymer molecule that repeats over and over again
difference between addition polymers and copolymers
addition polymers = one type of monomer
copolymers = two types of monomers in the same chain, alternating
key point about drawing polymerisation equations
ALWAYS DRAW EVERYTHING VERTICALLY
what type of bonds are between polymer chains?
london forces
how are alcohols bonded in polymers?
hydroxyl groups bond by hydrogen bonding due to slight dipoles on oxygen and hydrogen. bonding of two hydroxyl groups together is stronger than a hydroxyl group and a hydrogen
chain length determining properties of polymers
longer chains have stronger polymers as more london forces (more electrons)
side groups determining properties of polymers
polar side groups (e.g. hydroxyl) form stronger attraction between chains
branching determining properties of polymers
branching forms weaker polymers because can’t pack together as well, unbranched polymers = more crystalline and stronger.
stretching plastic organises chains more closely so temporarily stronger before intermolecular bonds broken
cross-linking determining properties of polymers
increases mpt because chains more difficult to separate
high density poly(ethene)
linear chains, strong, high density
low density poly(ethene)
branched chains, weak, flexible, low density
uses of poly(ethene)
plastic supermarket bags, shampoo bottles, children’s toys
PVC
poly(chloroethene) aka poly(vinyl chloride)
uses of PVC
gutters, records and windows
uses of tetrafluoroethene
non-stick pans, electrical/cable insulation
types of phenyl(ethene)
expanded, not expanded
other name for phenyl(ethene)
poly(styrene)
uses of expanded phenyl(ethene)
cups, packaging materials, thermal insulation
uses of not expanded phenyl(ethene)
toys, yoghurt pots
thermoplastics
no cross-linking, weak attraction between chains so low mpt, easy to mold when heating
thermosets
extensive cross-linking, strong attraction between chains so polymer keeps shape upon heating
methods of disposal of waste polymers
- recycling
- PVC recycling
- combustion for energy production
- feedstock recycling
recycling +/-
+ conserves finite fossil fuels
+ decreases waste to landfill
- discarded polymers must be sorted by type (unusable if mixed)
PVC recycling +/-
- high chlorine content and additives present so disposal and recycling hazardous
- releases HCl gas when burned (gas corrosive) and other pollutants (toxic dioxins) - can be removed from the waste gases by passing gas through alkali/carbonate
+ solvent reused
recycling
sorted, chopped into flakes, washed, dried, melted, cut into pellets, used by manufacturers
PVC recycling
solvents dissolve the polymer, PVC recovered from precipitation from solvent
combustion for energy production +/-
+high stored energy level
-pollutants
why can some polymers only be used in combustion?
polymers derived from petroleum/natural gas are difficult to recycle
feedstock recycling +/-
+ able to handle unsorted and unwashed polymers
what is feedstock recycling?
chemical and thermal processes to reclaim monomers/gas/oils from waste polymers, products = raw materials
what are bioplastics?
produced from plant starch, cellulose, plant oils and protein. conserves oil reserves because not oil based
what can be used as a starting material in the production of bioplastics?
sugar cane
biodegradable polymers
- broken down by microorganisms into water, CO2 and biological compounds
- composed of starch or cellulose or contain additives to change polymer structure to be broken down by microorganisms
compostable polymers
degrade and leave no visible or toxic residues
alternative to alkene-based polymers
compostable polymers based on poly(lactic acid)
examples of using compostable polymers
- bags made from plant starch used as bin liners for food waste so bag and waste can be composted together
- plates, cups and food trays made from sugar cane fibres to replace expanded polystyrene
photodegradable polymers
a type of oil-based polymer used when plant-based alternatives aren’t possible.
contain bonds weakened by absorbing UV light to start degradation. light-absorbing additives could be added
