4.1 key concepts Flashcards
What is meant by a homologous series?
A series of organic compounds having the same functional group but with each successive member differing by CH2
What is meant by a functional group?
A group of atoms responsible for the characteristic reactions of a compound
What is meant by a saturated compound?
Only contains carbon – carbon SINGLE bonds
What is meant by an unsaturated compound?
A compound contain DOUBLE bonds
What is meant by aliphatic?
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non - aromatic rings
What is meant by alicyclic?
An aliphatic compound arranged in non-aromatic rings with or without side chains
What is meant by aromatic?
A compound containing a BENZENE ring
Name all the alkane/alkene stems from compounds with 1-10 carbon atoms joined together
1 - Meth 2- Eth 3 - Prop 4 - But 5 - Pent 6 - Hex 7 - Hept 8 - Oct 9 - Non 10 - Dec
What is the functional group for alkanes?
C-C
What is the functional group for alkenes?
C=C
What is the functional group for a haloalkane?
C-X
X = halogen
What is the functional group for an ester?
-COO
What is the functional group for an alcohol?
-OH
What is the functional group for an aldehyde?
-CHO
What is the functional group for a ketone?
-CC=OC
What it the general formula for an alkane?
CnH2n+2
What it the general formula for an alkene?
CnH2n
What is the general formula for a cycloalkane?
CnH2n+2
What is the general formula for an alkyl chain?
CnH2n+1
What are the names of the side chains containing carbon? (alkyl groups)
Methyl Ethyl Propyl Butyl Pentyl
What is the ending of an alkane?
-ane
What is the ending of a alkene?
-ene
What is the ending of an alcohol?
-ol
What is the ending of a carboxylic acid?
-anoic acid
What is the ending of an ester?
-yl anoate (double check)
What is the ending of an aldehyde?
-al
What is the ending of a ketone?
-one
Rules you need to follow when naming organic compounds?
1) Count the carbons in the LONGEST chain
2) Find the main functional group
3) Number the functional group so it is as LOW as possible
4) Any - side chain, other functional groups are given numbers . If there is more than 1 then put in them in ALPHABETICAL order
5) If there are more than one identical side chain use:
di - 2
tri- 3
tetra - 4
What is the nomenclature naming order?
Prefix then Stem then Suffix
What are the different names for halogenoalkanes?
Iodo
Fluro
Bromo
Chloro
What is a structural isomer?
Compounds with the same molecular formula but different structural formulae
What are 3 different types of structural isomers?
Chain length isomer - Same molecular formula but different longest chain lengths (could be due to branching)
Positions of the functional group on the chain - Same molecular formula but different position of the functional groups
Different functional group completely - Same molecular formula but different functional group
When using the skeletal formula, what is the best thing you can do?
Label all the corners with a C, you’ll never get confused with this
Describe the boiling point between isomers
- “straight” chain isomers have high boiling points than branched chain isomers. The greater the degree of branching, the lower the boiling point. This is because branching decreases the effectiveness of intermolecular attractive forces which reduces surface contact. As surface contact decreases less energy has to be put in to separate the molecules.
Boiling point also may vary between isomers containing different functional groups
What is meant by homolytic fission?
Where a covalent bond breaks EVENLY and each bonded atom receives one electron from the bonded pair forming two radicals.
What is meant by heterolytic fission?
Where a covalent bond breaks UNEVENLY and both electrons go to the more electronegative atom (out of the bonded atoms) This creates 2 ions, 1 positive and 1 negative
What is a radical?
A highly reactive species with one or more unpaired electrons
What is a curly arrow?
Shows the movement of an electron pair during a reaction
What is the process called that turns alkanes into haloalkanes?
Free radical subsitution
What conditions are required in free radical substitution?
Reagents - Halogen and alkane
Conditions - UV light
Outline each step of a free radical subsitution reaction
Initiation = X2 (and UV light) → 2X•
Propagation = X• + CH4 → CH3 • + HX
CH3• X2 → X• + CH3X
Termination = X• + X• → X2
CH3• + CH3• → C2H6
CH3• + X• → CH3X
What happens during initiation?
2 radicals, made via homolytic fission using UV light
What happens during propagation?
1 radical and 1 non-radical react together creating a chain reaction (radicals are used and regenerated)
What happens during termination?
2 radicals reaction together to form a non-radical. (mixture of products)
Mixture of products - If there is sufficient halogen etc chlorine, every halogen will eventually be replaced.
Problems with this could be low percentage yield and its expensive
Are alkanes saturated or unsaturated and why? What this this mean?
Saturated as they single - single bonds. This means that alkanes are fairly unreactive as the strong sigma bonds requires a lot of energy to break down
What is a π bond?
A covalent bond resulting from the formation of a 2 p orbitals by side-to-side overlap
Name some characteristics of π bonds
- Side-to- side overlap
- Lower bond enthalpy
- Electron density above and below bonding atoms
- Low electron density
- Weaker than sigma bonds
What is a σ bond?
A covalent bond resulting from the formation of a molecular orbital by the end-to-end overlap of atomic orbitals
Name some characteristics of σ bonds
- Can occur by: s and s end to end overlap p and p end to end overlap s and p end to end overlap - It is between bonding atoms and nuclei - End to end overlap - Higher bond enthalpy - Electron density is between bonding atoms - High electron density - Stronger than pi bonds
What is the shape of an alkane and why?
An alkane has the shape of a tetrahedral due to its 4 bond pairs. This means it has a bond angle of 109.5. It has this bond angle due to the shape keeping repulsive forces to a minimum
Describe the boiling point of alkanes
Increases with more carbon atoms in the formula
The more atoms there are, the greater the induced dipole dipole forces between molecules. Greater intermolecular forces means MORE ENERGY is needed to separate molecules. The more energy needed means higher boiling point
Note: As chain length increases, boiling point increases
What affect does branching have on the boiling point of alkanes?
The greater the degree of branching, the lower the boiling point. This is because branching decreases the effectiveness of intermolecular attractive forces which reduces surface contact. As surface contact decreases less energy has to be put in to separate the molecules.
State and explain the solubility of alkanes in water and organic compounds
Alkanes are insoluble in water due to their non-polar bonds.
A substance will dissolve if there is enough energy released when new bonds are made between the substance and the water to make up for what is used in breaking the original attractions.
Alkanes are soluble in organic compounds
When an alkane dissolves in an organic solvent, you are breaking Van der Waals forces and replacing them by new Van der Waals forces. The two processes more or less cancel each other out energetically - so there isn’t any barrier to solubility.
Why is complete combustion of alkanes good?
It can make useful fuels such as kerosene, petrol and Naphtha
What products are produced in complete combustion and what conditions are needed?
Condition - Excess oxygen
Product - ALWAYS CO2 and H20
Why is incomplete combustion bad?
It produces carbon monoxide which is a toxic gas which can cause death
What products are produced in incomplete combustion and what conditions are needed?
Conditions - Limited oxygen
Products - Carbon monoxide or soot and H20
In a single bond how many sigma and pi bonds are there?
Sigma - 1
Pi - 0
In a double bond how many sigma and pi bonds are there?
Sigma -1
Pi - 1
In a triple bond how many sigma and pi bonds are there?
Sigma -1
Pi - 2
Are alkenes saturated or unsaturated?
Unsaturated. This means that they are reactive as the C=C bond can break due to the weak pi bond.
What is shape in alkenes called and why?
Trigonal Planar with a bond angle of 120 due to ???
What is a stereoisomer?
Organic compounds with the same molecular formula and structural formula but having a different arrangement in space
What forms can a stereoisomer come in?
Either cis (Z) or trans (E)
What is cis-trans isomerism?
Cis-trans isomerism is a special type of E/Z isomerism where substituents on each carbon atom are the same
What is meant by Cis?
Groups/atoms are on the same side of the double bond
What is meant by Trans?
Groups/atoms are on OPPOSITE sides across the double bond
When will stereoisomerism not occur?
Once you get two similar atoms/groups attached to one end of a C=C
When can E/Z isomerism occur?
Only in alkenes!
When will E/Z isomerism NOT occur?
- In alkanes
- Where the atoms attached to one carbon in the double bond are the same
What is meant by E?
The priority groups are on different sides
What is meant by Z?
The priority groups are on the same side
What are Cahn - Ingold Prelog rules?
1) Locate the C=C double bond in the molecules and REDRAW it to show the substituents.
2) Focus on 1 carbon atom and assign the PRIORITY of each substituent based on its relative atomic mass. The highest relative atomic mass is GIVEN priority. Then assign priority to the second carbon atom
3) If the highest priority groups are on the SAME side of the C=C double bond, then the isomer is Z
If the highest priority groups are on DIFFERENT sides of the C=C double bond, then the isomer is E
Why do C=C bonds have restricted rotation and what does it mean?
C=C bonds have restricted rotation so the groups on either end of the bond are “FROZEN” in one position
NOTE: It isn’t easy to flip the two. This produced 2 possibilities. The 2 structures CANNOT interchange easily so the different
Describe the reactivity of alkenes
Alkenes are reactive due to the pi bond which has a low bond enthalpy which means not much energy is needed to break the bond. The pi bond is always broken first. This means that alkenes are reactive.
What is the process called that turns alkenes into alkanes?
Hydrogenation (Addition of hydrogen)
What conditions are required in hydrogenation?
Reagent - Hydrogen
Conditions - Nickel catalyst - finely divided. (Finely divided as it increase the surface area which will increase the rate of reaction
Outline the general equation for hydrogenation
Alkene + Hydrogen (g) → Alkane
Outline the equation for hydrogenation for ethene to ethane
Ethene (g) + Hydrogen (g) → Ethane (g)
C2H4 (g) + H2 (g) → C2H6
What do we use hydrogenation for?
Margarine manufacture
What is the process called that changes alkenes into alcohols?
Direct hydration (Adding water (g))
What conditions are required for direct hydration?
Reagent - Steam (330 degrees celsius)
Condition - High pressure (6MPa)
Catalyst - Phosphoric acid (H3PO4)
Outline the general equation for direct hydration?
Alkene + Water ⇌ Alcohol
Outline the equation for direct hydration of ethene to ethanol
Ethene + Water (g) ⇌ Ethanol
C2H4 (g) + H20 (G) ⇌ C2H5OH
What is the process that turns an alkene into a dihaloalkane called?
Electrophilic addition
What conditions are needed for electrophilic addition?
Room temperature
Outline the equation of an alkene reacting with any halogen
C2H4 (g) + X2 → C2H4X2
Where X = Cl, I or Br
Outline the general word equation of an alkene reacting with any halogen
Alkene + Any halogen → Dihaloalkane
What is the general equation for the electrophilic addition of alkene reacting with a halide?
Alkene + Hydrogen Halide → Halogenoalkane
A hydrogen halide is a hydrogen halogen e.g. Hydrogen Bromide , HBr
What is equation for the electrophilic addition of ethene reacting with HBr?
C2H4 (g) + HBr (g) + ROOM TEMP → C2H5BR
What reagent and condition is required in this reaction?
Condition - Room temperature
Reagent = Hydrogen bromide: It is electrophilic because the H is slightly positive so it makes the Br slightly negative.
Electrophilic addition can only take place in polar molecules
Provide examples of electrophiles
(insert)
Provide examples of electrophiles
H2SO4 - Sulphuric acid X2 - (Where X is either Cl, F. Br or I) NO2+ - Nitronium ion H+ - Hydrogen ion H-X (Where X is a halogen)
What is a curly arrow?
Shows the movement of an electron pair during a
When looking at reaction mechanism what must you always show?
- Reaction name
- Conditions and Reagents
- Curly arrow
- Partial charges
- Intermediate (Carbocation)
Show the weakest to strongest carbocation
Weakest
Primary carbocation
Secondary carbocation
Tertiary carbocation
StrongestWhat is meant by primary carbocation?
When the carbon ion is attached to 1 other carbon atoms
What is meant by secondary carbocation?
When the carbon ion is attached to 2 other carbons atoms
What is meant by tertiary carbocation?
When the carbon ion is attached to 3 other carbon atoms
How is the minor product formed?
Via primary carbocation
How is the major product formed?
Via either secondary or tertiary carbocation (Tertiary more preferable if it available)
What does Markownikoff’s rule state?
When a compound HX (hydrogen halide) is added to an unsymmetrical alkene such as propene, the hydrogen becomes attached to the carbon with MOST HYDROGENS ATTACHED to it already
Describe methyl carbocation
C+ attached to 3 other carbons
Describe primary carbocation
C+ attached to 1 carbon and 2 hydrogens
Describe secondary carbocation
C+ attached to 2 carbons and 1 hydrogen
Describe tertiary carbocation
C+ attached to 3 carbons ad NO hydrogens
What 2 types of products called using Markownikoff’s rule?
Minor product
Major product
How do you know if the product is a major product?
In forming, two possible isomeric products, one of the carbocation intermediates will be MORE STABLE than the other and that isomer will be the MAJOR PRODUCT, sometimes the only product formed
How do you know if the product is a minor product?
In forming, two possible isomeric products, one of the carbocation intermediates will be LESS STABLE than the other and that isomer will be the MINOR PRODUCT, sometimes the only product formed
Again, what is the most important rule for Markownikoff’s rule?
The HYDROGEN will always add to the carbons tom that ALREADY has the MOST hydrogen atoms attached. This will form our MAJOR product
Out of the hydrogen halides (HF,HI,HCl and HBr) which one is the most reactive?
HI is the most reactive as it has the most outer shells. This means that the outermost electron is less attracted to the nucleus so is lost easier than the other halides., making it the most reactive
What is meant by addition polymerisation?
When an alkene undergoes a addition reaction with itself forming a long hydrocarbon chain
Name 3 ways you can dispose polymers
- Reuse
- Landfill
- Incineration
Outline the process of reusing plastics
- Can be recycled by remoulding them (melted down and then remoulded into something new). These can be created into smaller monomer units.
- However a problem with recycling is that we need to separate these plastics out and not all plastics can be recycled so there is a COST aspect to this aswell.
- Furthermore, energy is needed to be put in to melt the plastic and remould them so its not completely environmentally friendly
Outline the process of landfill
Burying the waste in a big hole in the ground.
- This is very expensive.
- These plastics are too difficult to recycle as they are very stable and unreactive
- This form of disposal is used for some plastics that are difficult to separate from other waste
Outline the process of incineration
- Plastics are mainly organic and can be burned to produce electricity. They contain a large number of carbons which releases carbon dioxide during combustion.This is a greenhouse gas and is linked to global warming and climate change
- Depending on the plastic other toxic chemicals like HCl (from PVC) can be made .These gases can be removed by using gas scrubbers. This contains a base Calcium oxide that neutralises the acidic gas
Biodegradable plastics
- To have a biodegradable plastic it must be able to be broken down by environmental conditions or microorganism
- Sometime a biodegradable polymer like plant starch is mixed with an addition polymer
- This means over time the polymer can be broken down making the polymer chain smaller and the material biodegradable
- However there is concerns over the small pieces of addition polymers may still cause hazards to the ecosystem
Photodegradable plastics
- Photodegradable plastics break down chemically using energy with wavelengths similar to light
- Addition polymers can have bonds (ester bonds) within the structure that are weakened by absorption of light
- Addition polymers can have additives that are affected by light which then weakens the polymer.
- Once exposed to light the polymer starts to breakdown in an irreversible process.
However photodegradable plastics in landfill may not be exposed to sufficient light to degrade
Bioplastics
- If only biodegradable plastic is used then it is a bioplastic
- Plant starch can be used to make bin bags
- If the starch is derived from sustainable farming methods then the material could be classified as ‘carbon neutral’
Compostable plastics
- To be fully compostable a plastic must decompose landfill material as quickly as compost would form from grass clippings and other green waste
- The only products should be carbon dioxide, water, inorganic compounds and biomass
- Polylactic acid is an example of this and is used in disposable utensils and drinking cups
