A2 Structures, Reactions And Properties Of Commercially Important Organic Compounds Flashcards

1
Q

General formula for alkanes

A

CnH2n+2

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2
Q

Structural isomer

A

Have the same molecular formula but different structural formula.

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3
Q

Chain isomer

A

Molecules with the same molecular formula but different arrangement of carbon atoms.

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4
Q

Naming branched chain alkanes

A

1) find the longest carbon chain (name eg butane)
2) find any side chains and name (eg methyl)
3) number the side chains
Eg 2-methylbutane

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5
Q

Complete combustion

A
  • short chain alkanes are valuable fuels
  • when there is plentiful supply of oxygen it undergoes complete combustion to form carbon dioxide and water.
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6
Q

Uses of Methane and it’s equation for complete combustion

A
  • main constituent of natural gas used for heating and cooking
  • CH4 + 2O2 = CO2 + 2H2O
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7
Q

Incomplete combustion

A

When there is a limited amount of oxygenation carbon monoxide gas, or carbon and water is formed.

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8
Q

Incomplete combustion of methane

A
  • CH4 + 3/2 o2 = CO + 2H2O
  • CH4 + O2 = C + 2H2O
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9
Q

What make’s intermolecular forces stronger (in alkanes) ?

A
  • alkanes have induced dipole dipole forces
  • these get stronger when there are more electrons
  • larger alkane- stronger intermolecular force
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10
Q

How can a change of shape affect the boiling point of alkanes?

A
  • when the surface area of the molecule decreases but the number of electrons stay the same the boiling point decreases.
  • this is because there is less surface contact and weaker intermolecular force.
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11
Q

Formula for alkenes

A

CnH2n

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12
Q

Positional isomerism

A

Molecules with the same molecular formula which have the functional group on different positions in the molecule.

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13
Q

Functional group isomerism

A

Molecules with the same molecular formula but different functional groups.

  • cycloalkanes and alkenes can show functional isomerism. Cycloalkanes have the same formula as alkenes CnH2n
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14
Q

Stereoisomer

A

molecules with the same structural formula but a different arrangement of the atoms in space eg but-2-ene CH3CH = CHCH3

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15
Q

Why do stereoisomers occur?

A
  • double bonds restrict rotation
  • when 2 different groups are attached to the carbons in the double bond
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16
Q

Sp3 hybridisation - methane, CH4

A
  • the s orbitals increases in energy
  • the p orbitals decrease in energy
  • all orbitals contain 1 electron
  • the hybrid orbitals all have the same size and shape.
  • 1s and 3p orbitals combine
  • this makes 4 sp3 hybrid orbitals
  • there are no spare p orbitals
17
Q

What bonds do sp3 hybridisation form?

A

-All hybrid orbitals form sigma bonds (single bonds)
- they do not form double bonds as there are no electrons in p orbitals

18
Q

Sp3 bond angle

A

109.5 degrees

19
Q

Sp2 hybridisation- ethene C2H4

A
  • the s orbital increases in energy
  • the p orbital decreases in energy
  • all orbitals contain one electron
  • the hybrid orbital all have the same size and shape.
  • 1s and 2p orbitals combine
  • this makes 3 sp2 hybrid orbitals
  • there is one spare p orbital
20
Q

What binds do sp2 hybridisation make?

A

As there are 3 hybrid orbitals they form sigma bonds. There are spare p orbital electrons on each carbon which overlap to form pi bond which makes the double bond.

21
Q

Sp hybridisation- ethyne C2H2

A
  • s orbital increases in energy
  • p orbital decrease in energy
  • all orbitals contain 1 electron
  • the hybrid orbital all have the same shape and size
  • 1s and 1p orbitals combine
  • this makes 2 sp hybrid orbitals
  • there are 2 spare p orbitals
22
Q

CH4 + cl2 = CH3Cl + HCl Free radical substitution mechanism

A

Initiation
- A free radical contains a single unpaired electron.

  • Uv light provides the energy needed to break the cl-cl bond (halogen-halogen)
  • both cl have donated one pair of electrons into the covalent bind
  • this is called homolytic fission
  • cl2 = 2Cl•

Propagation
- Cl• + CH4 = HCl + •CH3
- •CH3 + Cl2 = CH3Cl + Cl•
The second propagation reaction forms the desired haloalkane product and generates another chloride radical which can react again and again.

Termination
- this is where the free radicals combine
- Cl• + Cl• = Cl2
- •CH3 + •CH3 = C2H6
- •CH3 + Cl• = CH3Cl

23
Q

Ethanol uses

A
  • as an intermediate in the synthesis of other organic chemicals
  • as a solvent in cosmetics and perfumes
  • manufacture of drugs, detergents and inks
  • alcohol found in alcoholic drinks
24
Q

Producing ethanol from crude oil - hydration

A

Ethene is made when crude oil fractions are cracked to form an alkanes and alkene. Ethene is then hydrated with water in the presence of a concentrated phosphoric catalyst.

Ch2=Ch2 + H2O = CH3Ch2OH

Conditions 450 degrees, 50-100atm pressure

25
Q

Producing ethanol by fermentation

A
  • carbs in plants are converted into sugars which are then fermented into ethanol using enzymes from yeast.
  • C6H12O6 = 2CH3CH2OH + 2CO2

Conditions yeast enzymes , temp 35degrees, no oxygen

Too cold and the rate of reaction is slow
Too high temp enzymes can denature and stop working
No oxygen should be present ethanol can oxidise to ethanoic acid .

26
Q

Hydration of Ethene - pros cons

A

Advantages
- large scale production method
High purity product made
- readily available raw material
- high rate of reaction
- continuous product method

Disadvantages
- high temp and pressure needed which increase costs
- expensive and high tech equipment needed
- crude oil is non renewable

27
Q

Fermentation- pros cons

A

Advantages
- used renewable resources
- low tech method little expense needed
- readily available and renewable raw materials from plant
- low cost

Disadvantages
- slow rate of reaction
- impure ethanol made needs distilling
- causes food prices to rise if crops are used to produce alcohol instead of food
- batch production method- less efficient

28
Q

Explain why oil companies need to crack “heavy fractions”

A

As smaller chain molecules are higher in demand

29
Q

State the type of cracking that produces a high percentage of alkenes and give 2 conditions

A

Thermal cracking
Conditions - high temp and high pressure