4.1 & 2 Flashcards
Homologous series
A series of organic compounds having the same functional group with each successive member differing by CH2
Functional group
A group of atoms responsible for the characteristic reactions of a compound
Aliphatic
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
Alicyclic
An aliphatic compound arranged in a ring or without side chains
Aromatic
A compound containing a benzene ring
Saturated
Single carbon-carbon bonds only
Unsaturated
The presence of multiple carbon-carbon bonds, including double and triple carbon bonds and aromatic rings
Structural isomers
Compounds with the same molecular formula but with different structural formulae
Homolytic fission
In terms of each bonding atom, receiving one electron from the bonded pair, forming two radicals
Heterolytic
In terms of one bonding atom receiving both electrons from the bonded pair
Radical
A species with an unpaired electron
Alkanes
Saturated hydrocarbons containing single C-C and C-H bonds as sigma-bonds (with free rotation)
Sigma-bonds
Overlap of orbitals directly between the bonding atoms
Molecular orbital theory
Covalent bonds are formed by the overlap of atomic orbitals
Why can we draw alkanes in different ways
There is free rotation around these sigma bonds
Why do branched alkanes have low boiling points
Branched alkanes cannot pack together as well as linear alkanes
Less surface area of contact
So induced dipoles are less strong
Lower bp
Why do alkanes have low reactivity
Due to their high bond enthalpy
Not attracted to nucleophiles or electrophiles
C-C and C-H bonds are non polar
No partial charge anywhere
Shape of alkanes
Tetrahedral
Alkenes
Unsaturated hydrocarbons containing a double carbon bond comprising a pi-bond (restricted rotation) and a sigma-bond
Pi-bond
Sideways overlap of adjacent p-orbitals above and below the bonding C atoms
Shape of alkenes
Trigonal planar
Naming of alkenes
Stem, position of double bond, suffix
Stereoisomerism
Same structural formula but diff. arrangement of atoms in space
E/Z isomerism
Stereoisomer
Results from restricted rotation about the double bond
Requires 2 diff. groups to be attached to each carbon atom in the C=C group
Z isomers
Same group attached to both carbons, top and bottom
E isomers
Diff. group attached to both carbons, top and bottom
Formation of pi-bonds
P- orbitals perpendicular to C-C
Overlapping of orbitals
Cis isomerism
Usually Z isomers
Have higher bp
Polar
Have permanent dipole-dipole forces
Trans isomers
Non polar
Usually E isomers
Have higher mp
Pack more efficiently so IM forces maximise potential strength
Why are alkenes reactive
Exposed areas of high electron density that is attractive to electrophiles
Pi-bonds have a low bond enthalpy
Sigma-bonds in alkanes have higher bond
Addition reaction
When a reactant is added to an unsaturated molecule to make a saturated molecule
Breaks pi-bonds and forms sigma-bonds
Hydrogenation
H2 gas at high temp with Ni catalyst
1 mole of H2 per double bond
Alkenes react with:
H2 Halogens Hydrogen halides (HF/HCl/HBr/ HI) Other H-X molecules e.g. H2SO4 Steam
Hydration
Reaction with water
Conditions of hydration
Steam
H3PO4 catalyst
300 degrees
60 atm
Where do curly arrows start
A lone pair
Existing covalent bond
Markownikoff’s rule
H atoms/ least electro-ve atoms join the carbon which already has the most H atoms directly bonded (most stable carbocation)
Most stable carbocation intermediate
Tertiary (3’) - 3 alkyl groups
Secondary (2’) - 2 alkyl groups, 1 H
Primary (1’) - 1 alkyl group, 2 H
What happens when you add an alkyl group
Donate electrons to positive charge and minimise strength
General formula of alcohols
CnH(2n+2)O
Functional group of alcohols
Hydroxyl group: -OH
Naming of alcohols
The no. of the carbon to which the hydroxyl group is attached is written before the -ol
Making ethanol
Ethene (g) + water (g) –> ethanol (l)
Fermentation of sugar - C6H12O6 —> 2C2H5OH + 2CO2
Conditions to make ethanol
Phosphoric acid catalyst - dipole of water isn’t a strong enough electrophile
300 degrees
60 atm
Why does solubility of alcohols decrease with chain length
They behave more like hydrocarbons and the LF’s have a greater influence on solubility than the -OH group
Primary alcohols
OH bonded to C with 1 alkyl group
Secondary alcohols
OH bonded to C with 2 alkyl groups
Tertiary alcohols
OH bonded to C with 3 alkyl groups
Why do alcohols have high mp and bp
Hydrogen bonding
Which alcohols can be oxidised
Primary and secondary alcohol using a suitable oxidising agent e.g. acidified dichromate ions (Cr2O7 ^2-/ H^1)
What is the colour change in acidified dichromate ions when oxidised
Orange to green
Partial/mild oxidation of primary alcohols
Primary alcohol + [O] –> Aldehyde and water
Aldehydes
End in -al
C=OH functional group (always at the end; don’t need numbers)
Conditions of partial/mild oxidation of primary alcohols
K2Cr2O7/H2SO4
Distil immediately
Complete oxidation of primary alcohols
Primary alcohol + 2[O] –> Carboxylic acid + water
Conditions of complete oxidation of primary alcohols
K2Cr2O7/H2SO4
Reflux
Complete oxidation of secondary alcohols
Secondary alcohols + [O] –> Ketone + water
Conditions of complete oxidation of secondary alcohols
K2Cr2O7/H2SO4
Reflux
Ketones
End in -one
C=O carbonyl functional group
Can ketones be oxidised
No
Can tertiary alcohols be oxidised
No
Dehydration reaction
Alcohol –> alkene (in the presence of acid catalyst (conc. H3PO4/ H2SO4)), heated under reflux
Forming halogenoalkanes
Substitution with halide ions in the presence of acid (NaBr/H2SO4)
NaBr + H2SO4 —> HBR + NaHSO4
CH3CHOHCH3 + HBr –> CH3CHBRCH3 + H2O
Nucleophile
Electron pair donor
Examples of nucleophiles
OH ^-
Cl ^-
H2O
Haloalkanes
Compounds in which a halogen has replaced at least one hydrogen (CnH2n+1X)
Classification of haloalkanes
Primary, secondary and tertiary depending on no. of alkyl groups
What dictates the reactions of haloalkanes
The polarity of the C-halogen bond
What happens as a result of the carbon atom on the C-halogen bond being electron deficient
The partial positive charge attracts species with lone pairs (nucleophiles)
Nucleophilic substitution
Nucleophile replaces a halogen
CH3CH2I + OH –> CH3CH2OH + I
Ozone layer
O3
What do CFC’s do
Deplete the ozone layer
O3 + O (oxygen radical) –> 2 O2
Rates of hydrolysis in haloalkanes
Increase from F to I due to the decrease in bond enthalpies so ppt is formed faster in iodoalkanes and slowest in chloroalkane
Heterolytic fission
The breaking of a covalent bond to form an anion and cation as both electrons go to one species
Homolytic fission
The breaking of a covalent bond to form 2 radicals, with each species receiving one electrons
Happens in the presence of UV light
Equipment for reflux
Pear shaped flask Condenser Rubber tubing Stand and clamp Heat source
Why are anti-bumping granules used
So the contents boil smoothly without large bubbles forming, which will cause the glassware to vibrate
Apparatus for distillation
Round bottom or pear shaped flask Condenser Rubber tubing Heat source Stand and clamp Screw cap adaptor Receiver adaptor Thermometer
In samples of organic liquids, how do you identify the organic layer
Add water to the mixture. The layer that gets bigger is the aqueous layer
How to use a separating funnel
Ensure the tap is closed
Pour the mixtures in and put on a stopper before inverting
Allow layers to settle and identify the organic layer
Place conical flask under the separating funnel, remove the stopper and open the tap until the whole lower layer has left
Do the same for the second layer
How to purify products with any acid impurities
Add NaH/CaCO3 (aq) and shake the mixture in the separating funnel
Drying agent
Anhydrous inorganic salt that readily takes up water to become hydrated e.g. CaCl2, CaSO4, MgSO4
Which fragment ion has a m/z of 15
CH3 +
Which fragment ion has a m/z ratio of 29
C2H5+
Which fragment ion has a m/z ratio of 57
C4H9 +
Which fragment ion has a m/z ratio of 43
C3H7 +
Which fragment ion has a m/z ratio of 31
CH2OH
Which fragment ion has a m/z ratio of 45
C2H5O +
Using M and M + 1 peaks
Height of M + 1 peak/height of M peak * 100 = no. of carbon atoms
What does the amount that a bond stretch or bends depends on
Mass of atoms in the bond - heavier atoms vibrate more slowly than lighter ones
The strength of the bond - Stronger bonds vibrate faster than weaker bonds
Advantages of oil companies using cyclic alkanes
Lower boiling point so will burn more efficiently
What is the greenhouse effect of carbon dioxide dependent on
Abundance in atmosphere
Ability to absorb IR
CCS
Reacting CO2 and metal oxides (CaO)
Deep in oceans
CIP priority rules
If both high priority groups are at the top it’s a (Z) isomer
If they are diagonal, (E)
Benefits of developing biodegradable and photodegradable polymers
Reduced dependency on finite resources
Alleviating problems from disposal of persistent plastic waste
Cis-trans isomerism
Special case of E/Z isomerism in which 2 of the substituent groups attached to each carbon of the C=C group are the same
Disposal of waste polymers
Combustion which can produce energy
Use as organic feedstock for production of plastics
Dissolving halogenated plastics (PVC) so toxic HCl isn’t released
What does IR cause
Covalent bonds to vibrate more and absorb energy
Which bonds absorb IR
C=O
O-H
C-H
What is infrared spectroscopy used for
Monitor gases causing air pollution (CO and NO from cars)
Measure ethanol in the breath (breathalysers)
What is the M+1 peak caused by
Small proportion of carbon-13
When do we use cis/trans isomers
When each carbon in the double bond is attached to one H
Why does the bp of cycloalakanes increase
More carbons —> stronger London Forces
More energy need to overcome imf
Why do cycloalkanes get added to straight chain alkanes in petrol
So it burns more efficiently
What is the greenhouse effect of CO2 dependent on
Abundance in atmosphere
Ability to absorb IR
Why do we do reflux
To keep the product reacting in the reaction flask until collection
Liebig condenser
Allows the product to distill off and be collected
Why is ethanol used in the investigation about carbon-halogen bond enthalpy
So the reaction with AgNO3 is slow enough to be observed
What happens to bromine water in the presence of alkenes
Decolourises
Process of mass spectrometry
The IR causes the molecule to become charged and they are then accelerated through a capillary and detected
Heating under reflux
Boiling a liquid in a vertical container to prevent loss of products
How to remove acidic impurities
Shaking with potassium hydrogen carbonate ions
M/z peak of 45
COOH +
Why can cracking produce a variety of alkanes and alkanes w/ diff chain lengths
C-C bonds can break anywhere
Steps in purifying an organic liquid
Allow mixture to cool
(If reflux decant reaction mixture from the anti-bumping granules)
Use a separating funnel and discard aq layer
Dry using an anhydrous salt e.g. MgSO4 then filter off and discard
Redistillation - collect distillate in range just below (and up to) the bp of product
Why are there many products in free radical substitution
More than one C-H bond can be substituted
Lots of termination steps
Termination steps can give products that will also react w/ radicals
Feedstock recycling
Chemical or thermal processes which can use waste polymers to regenerate monomers, oils or gases so that new polymers can be produced
Why are there still concerns about ozone depletion
CFC’s are still being used
Other ozone depleting substances
Miscible with
Soluble in
Purifying a liquid that is miscible with water
Allow mixture to cool
Decant reaction mixture from anti-bumping granules, if reflux
Use separating funnel and keep aq layer
If acid is present use Na2CO3 (aq) until effervescence stops
Redistil
Purifying a solid product
Allow reaction mixture to cool
Filter under reduced pressure and leave impure product to dry
Recrystallise
Filter under reduced pressure, rinse w/ ice-cold water and leave the crystals to dry
Measure mp to assess purity
Repeat 2 previous steps if required
Filtering under reduced pressure
Using a Buchner funnel
Process of recrystallisation
Transfer impure solid to a boiling tube
Dissolve in minimum quantity of hot solvent (usually water)
Filter hot solution to remove any solid impurities
Allow filtrate to cool slowly to room temp, and then in an ice bath
Crystals will form
Determining mp of an organic solid
Ensure sample is dry
Add about 3mm of the sample to a sealed glass capillary tube
Measure mp using a Thiele tube setup
Mp of pure vs impure product
Pure products should have fairly narrow mp range
Impure products will have a LOWER and WIDER mp range
Experiment plan for rate of hydrolysis of haloalkanes
Measure 1cm^3 of each haloalkane and place in separate test tubes
Add 1cm^3 of ethanol solvent to each tube
Place in a water bath at 60 degrees
Once all tt have reached the same temp, add 1cm^3 of aq AgNO3 to one of the test tubes she use a stopwatch to time how long it takes for the ppt to form
Repeat w/ other two solutions
Heating alcohols under reflux
Place 2 cm^3 of acidified dichromate and 1 cm^3 alcohol (in excess) in a pear shaped flask and attach condenser
Heat sol. under reflux w/ a heating mantle
Distillation to form an aldehyde
Place the dichromate, acid and 1’ alcohol (in excess) in a pear shaped flask and attach a condenser
Use thermometer to ensure temp is below 100
Solution will turn green as the aldehyde is produced
-al can’t H bond and has the lowest bp
Collect distillate in the range just below (and up to) the bp of the -al. It will condense in the receiver
Carrying out TLC
Take a TLC plate and draw base line 1cm from one end of plate
Use a capillary tube and spot a small amount of sol onto base line
Prepare chromatography tank
Place the prepared TLC plate in the beaker, making sure that the solvent does not cover the spot
Cover the beaker w/ watchglass
Making a chromatography tank
This can be made from a small beaker w/ watchglass on top
Pour solvent into beaker to a depth of about 0.5 cm
Determining conc using gas chromatography
Measure the peak integration value of desired peak from compound X
Prepare some standard solutions of diff, known conc. of the compound X
Run these through the GC and ensure your peak integration values
Plot a calibration graph of peak integration value vs conc. and plot LOBF
Find the peak integration value and read off corresponding conc.
Limitations of free radical substitution
Further substitution occurs, producing a variety of products
Substitution can occur at different positions in the carbon chain
Produces several by-products lowering atom economy
Bond enthalpy of 1’, 2’ and 3’ haloalkanes
Tertiary has the lowest bond enthalpy so shortest time to react with silver nitrate
How is infrared spectroscopy used in identifying air pollutants
Indentifies bonds in pollutant
Match spectrum to known pollutants
Measures conc of pollutant
Naming esters
Stem is -ol attached to rhs
Suffix is -COOH attached to lhs
