Topic 6 - Organic I Flashcards
Homologous series
A series of compounds with the same functional group and similar chemical properties (e.g, alkanes)
Functional group
The group of atoms responsible for the characteristic reactions of a particular compound (e.g. COOH for carboxylic acids)
Empirical formula
the simplest whole number ratio of atoms of each element in a compound
Molecular formula
the true number of atoms of each element in a compound
General formula
All members of a homologous organic series follow the general formula e.g. CnH2n+2 for alkanes
Structural formula
shows the structural arrangement of atoms within a molecule without the bonds
Displayed formula
shows every atom and every bond in an organic compound
Skeletal formula
Shows only the bonds in a compound and any non-carbon atoms. The vertices are carbon atoms and hydrogen is assumed to be bonded to them unless stated otherwise.
Addition
reactants combine to form a single product
Substitution
one functional group is replaced by a different one
Elimination
reactions in which two atoms, or groups of atoms, are removed from a molecule to form a new product
Oxidation
when a species loses at least one electron and gains oxygen
Reduction
when a species gains at least one electron and loses oxygen
Hydrolysis
a reaction which uses water to break down a compound
Polymerisation
a reaction in which many small molecules (monomers) join together to form a long, repeating molecule (polymer)
Isomers
molecules with the same molecular formula but a different arrangement of atoms within the molecule
Position isomers
when the functional group of the molecule is in a different position on the carbon chain (e.g., propan-1-ol vs propan-2-ol)
Functional group isomers
isomers that have the same molecular formula but different functional groups (e.g. propanal vs propanone)
Stereoisomerism
molecules with the same molecular and structural formula but a different arrangement of atoms in space
E isomer
groups are on opposite sides of the double bond
Z isomer
groups are on the same side of the double bond
CIP Priority Rules
The first atom directly bonded to the carbon with the double bond with the highest Ar is given the higher priority
these groups are used to determine if it is the E or Z isomer
cis- trans- isomerism
a special case of E-Z isomerism
can only be used when there are hydrogen atoms to compare the two other groups to
General formula for alkanes
CnH2n+2
An alkane is which type of hydrocarbon?
saturated, as they do not contain double bonds
Fractional distillation
- mixture of hydrocarbons is vapourised and enters the fractionating column
- vapours rise, cool and condense
- products are collected for different uses
- short-chain hydrocarbons that have lower boiling points rise higher up the column before reaching their boiling point (and vice versa)
Reforming
the processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion
Cracking
the breaking down of long chain hydrocarbons into smaller, more useful molecules
Pollutants that form during combustion of alkane fuels
- carbon monoxide (toxic)
- oxides of nitrogen and sulfur (acidic)
- carbon particulates
- unburned hydrocarbons
Alternative fuels
- biofuels
renewable fuels
comes from living matter
biodiesel - made from refining renewable fats and oils
bioethanol - fermentation
carbon neutral
Homolytic fission
breaking a covalent bond so that each atom takes an electron from the bond to form two free radicals
Heterolytic fission
breaking a covalent bond so that the more electronegative atom takes both the electrons from the bond to form an anion, leaving behind a cation
Limitations of FRS
- collisions are uncontrollable, so FRS cannot be used to make one particular product
- more collisions are inevitable even after two propagations happen, causing further substitutions to happen
General formula for alkenes
CnH2n
Alkenes are what kind of hydrocarbon?
alkenes and cycloalkenes are unsaturated hydrocarbons, as they contain a C=C double bond
π bond
a covalent bond formed when p orbitals of two carbon atoms overlap with each other (formed above and below the plane of the molecule)
σ bond
a covalent bond formed from the end to end overlap of atomic orbitals
Electrophile
a chemical species which is attracted to electrons
Relative stability of carbocation intermediates
tertiary > secondary > primary > methyl
In a tertiary carbocation, where the positively charged carbon is attached to three alkyl groups, there is maximum electron donation to stabilise the positive charge.
Bromine water test
alkenes cause bromine water to change from orange-brown to colourless as C=C bond can ‘open up’ to accept bromine atoms to become saturated
Hydrogenation of alkenes
- hydrogen
- nickel catalyst
- 160 degrees
electrophilic addition whereby alkanes are produced
used in manufacture of margarine from unsaturated vegetable oils
Halogenation of alkenes
- halogens add across the double bond
- each carbon atom bonds to one halogen atom
- electrophilic addition
Hydrogen halides and alkenes
- halogenoalkanes formed
- electrophilic addition
Reaction of alkenes with steam
- forms alcohols
- steam hydration
- 300˚
- 60-70 atom
- phosphoric acid catalyst
Reaction of alkenes with potassium manganate
- shake alkene with acidified potassium manganate(VII)
- purple solution decolourised, oxidised alkene to diol
e.g. ethene -> ethane-1,2-diol
Disposal of polymers
- recycling
- incineration to release energy
- use as feedstock for cracking
How to limit problems caused by polymer disposal
- developing biodegradable polymers
- removing toxic waste gases by incineration of plastics
Nucleophile
an electron-rich species that can donate a pair of electrons
Halogenoalkanes
- contain polar bonds since halogens are more electronegative than carbon
- electron density is drawn towards hydrogen, forming 𝝳+ and 𝝳- regions
Halogenoalkanes -> alcohols
- halogenoalkanes react with aqueous KOH or NaOH
- nucleophilic substitution
- hydroxide ion acts as nucleophile
Halogenoalkanes and silver nitrate
- broken down using silver nitrate and ethanol
- water acts as nucleophile, which leads to breakdown of halogenoalkane, releasing halide ions into the solution
- halide ions react with silver ions to form silver precipitates
Halogenoalkanes -> nitriles
- react with KCN to form nitriles
- nucleophilic substitution
- CN- acts as nucleophile
- reaction adds one carbon atom
Halogenoalkanes -> amines
- react with alcoholic ammonia (e.g. ethanolic NH3)
- nucleophilic substitution
- Ammonia is nucleophile
Halogenoalkanes -> alkenes
- react with ethanolic potassium hydroxide (KOH) to produce alkenes
- elimination
- hydroxide ion acts as base
Relative reactivity of halogenoalkanes
tertiary > secondary > primary
Trend in reactivity of chloro-, bromo- and iodoalkanes in terms of bond enthalpy
C-I
weakest bond, lowest bond enthalpy, bond breaks easier, react faster
the larger the halogen, the longer the C-X bond, so the lower the bond enthalpy
Alcohol + oxygen products
carbon dioxide + water
Alcohol + halogenating agents
- nucleophilic substitution
- -OH group is replaced by a halogen, producing a halogenoalkane
Alcohol -> choloroalkanes
- PCl5
- can be used to test for alcohols as white fumes produced turn damp blue litmus paper red
Alcohol -> bromoalkanes
- 50% concentrated sulfuric acid + potassium bromide
- potassium bromide reacts with sulfuric acid to form HBr
- this then reacts with the alcohol to produce the bromoalkane
CH3CH2OH + HBr -> CH3CH2Br + H2O
Alcohol -> iodoalkanes
- red phosphorus and iodine
- phosphorus reacts with iodine to produce phosphorus (III) iodide
- this then reacts with the alcohol to form the iodoalkane
2P + 3I2 -> 2PI3
3CH3CH2OH + PI3 -> 3CH3CH2I + H3PO3
Oxidation of alcohols
primary alcohols -> aldehydes -> carboxylic acids
secondary alcohols -> ketones
tertiary -> not oxidised
potassium dichromate (VI) in dilute sulfuric acid
alcohols -> alkenes
- concentrated phosphoric acid
- elimination
- dehydration (water removed from alcohol)
Fehling’s solution colour change
- gently warm
- aldehyde present = red precipitate
- no aldehyde = remains blue
Heating under reflux
- vertical Liebig condenser
- continuously boil and evaporate mixture
- vapours evaporate, condense and return to the flask for further heating
Distillation
- pear-shaped flask heated
- liquid with lower boiling point will evaporate first
- it rises out of the flask into tubing surrounded by condenser
- condenser cools and condenses vapour back into liquid
- liquid is collected in separate flask
Extraction with solvent in separating funnel
- pour mixture in separating funnel
- add water
- shake funnel
- separate organic and aqueous layer
- collect in two different containers
Drying with anhydrous salt
- add anhydrous salt
- will absorb moisture and water present, drying and purifying compound
- common salt is sodium sulfate
