Chemistry- Organic Chemistry Flashcards
Define Homologous series
Family of chemicals with the same functional group or general formula
What is the difference between alkanes and alkenes?
Alkane:
- CnH2n+2
- Saturated hydrocarbons
- Single carbon bond (sigma bond)
Alkene:
- CnH2n
- Unsaturated hydrocarbon
- Double carbon bond (pi Bond)
What are the main products produced by thermal cracking?
High percentage of small alkenes such as Ethene
Also forms one or more small alkanes and one alkene molecule (naptha)
What are the conditions used during thermal cracking?
- Very high temperatures (400-900 degrees)
- High pressure (70 atmospheres = 7000KPa)
- No catalsyt
What are the conditions used during catalytic cracking?
- High temperature (450 degrees)
- Slight pressure (1 atmosphere)
- A ZEOLITE catalyst is also used which is silicon dioxide + aluminium oxide in a honeycomb structure to increase Surface Area
What are the products produced from catalytic cracking?
- Branched Alkanes (fuels)
- Cycloalkanes (fuels)
- 2-methlyheptane (petrol)
- Aromatic hydrocarbons
What is Isomerism?
2 or more compounds have the same molecular formula but different arrangement of atoms.
Isomers may have different physical and chemical properties (dependant on the type of isomerism)
What are the 2 main types of isomerism?
What kind of Isomers come under each type?
structural isomers -Chain
- Positional
-Functional group
Sterioisomerism - Geometrical
- Optical
What are general structural isomers?
Have the same molecular formula but their structural formulas are different.
What is chain isomerism?
Same molecular formula and functional group but their arrangement of the carbon atoms in the chain are different.
What are positional isomers?
Same molecular formula and functional group but the position of the functional group is different.
What are functional group isomers?
Same molecular formula but their functional group is different.
Eg. CH3CH2CH2CHO Butanal
Eg. CH3CH2COCH3 Butanone
What are geometric isomers?
Have the same structural formula but the bonds are arranged differently in space.
Geometric isomers often occur with a double bond.
When do geometric isomers occur?
When there is a double bond between 2 carbon atoms which have 2 different groups on them resulting in E and Z isomers.
How do you name geometric isomers?
If two atoms with the greatest atomic numbers are on the same side of the double bond it is a Z isomer. If they are on opposite sides then it is an E isomer.
E (trans) = Opposite side of c=c double bond
Z (cis) = Same side of c=c double bond.
What is an electrophile?
An atom which is electron deficient and therefore is attracted towards an electron dense area of another molecule during an organic reaction.
An electron pair acceptor
How can alkanes (unreactive) be attacked?
By very reactive free radicals.
What is a Haloalkane?
A group of chemical compounds derived from alkanes with one or more halogens bonded to them.
What mechanism do you use to show the formation of haloalkanes?
Free radical substitution.
What are the steps in doing a free radical substitution mechanism?
1) Initiation
2) Propergation
3) Termination
This reaction is a chain reaction process.
What is Ozone and what is its structure?
O3 but there is a dative covalent bond within the structure resonating between the 3 oxygen molecules.
Why is the Ozone layer important to the earth?
Ozone filters out harmful UV radiation from the sun.
What were CFC’s used for? (chloroflourocarbons)
Refrigerants
aerosols
What is the problem with having CFC’s in the atmosphere?
UV light can break the C-Cl bonds creating free radicals of .Cl Which may react with with the O3 causing a chain reaction and a constant overall reaction of 2O3 —–> 3O2.
What are haloalkanes susceptible to attack from?
Nucleophiles.
What is a nucleophile?
A species which can be electron pair donors.
:OH- Hydroxide ion
:CN- Cyanide ion
:NH3 Ammonia molecule (no charge)
What are free radicals?
A uncharged molecule which is highly reactive and difficult to control.
What are the conditions for an electrophilic addition reaction?
- Alkenes
- High electron dense region for electrophiles to attack
- Pi bond is broken
- Electrophiles (electron pair acceptor)
Hydrogen halides (H-Br)
H2SO4 Sulphuric acid
Bromine
What rule is needed when reacting a hydrogen halide to an alkene?
Markovnikov’s Rule:
The hydrogen bonds to the carbon with the most hydrogens.
The addition of hydrogen causes the carbo-cation on a neighbouring carbon. This is more stable energetically and therefore the activation energy for this reaction is lower.
What are the conditions needed for a nucleophilic substitution reaction to occur?
- Nucleophile (OH-/CN-/NH3)
- Aqueous conditions of ethanol
- Heat but not as much as in elimination
- Conc excess ammonia
What happens to the reactivity of the carbon halogen bond down the group?
Down a group the rate of reaction increases as the strength of the carbon halogen bond decreases (becomes less polar). Each halogen (except iodine) is more electronegative than carbon and therefore the electron pair in the C-X bond is pulled towards the halogen leaving the carbon slightly positive.
What are the conditions needed for free radical substitution reaction?
UV light.
Draw the Initiation, Propergation and Termination steps for the free radical substitution between Chlorine and methane.
Initiation:
CL2 ——> 2Cl.
Propergation:
CH4 + Cl. —–> .CH3 + HCL
.CH3 + Cl2 ——-> CH3Cl + Cl.
Termination:
Cl. + Cl. —-> Cl2
.CH3 + .CH3 —–> C2H6
.CH3 + .Cl —-> CH3Cl
What conditions are needed for elimination reactions?
- Concentrated OH- (KOH/NaOH Conc)
- Dissolved in alcohol
- Heat
Forms Alkenes.
What reagents are used in free radical substitution?
Cl2
Br2
What reagents are used in electrophilic addition?
Br2
Hydrogen Halides (H-Br)
H2SO4
What reagents are used in nucleophilic substitution?
:OH-
:CN-
:NH3
What reagents are used in Elimincation reactions?
Conc :OH-
