4.1.3 - Alkenes Flashcards

1
Q

What are alkenes?

A

Unsaturated hydrocarbons that contain at least one C=C bond made up of a pi bond and a sigma bond

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2
Q

What is the general formula of alkenes?

A

Cn H2n

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3
Q

How is a pi bond formed?

A

Electrons in the adjacent p orbitals overlap above and below the carbon atoms. They can only be made after a sigma bond is formed

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4
Q

What bond restricts the rotation of carbon atoms?

A

pi bond

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5
Q

What is the angle and shape of a double bond?

A

Trigonal planar

120

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6
Q

Are they more or less reactive than alkanes?

Why?

A

More reactive due to high electron density of double bond and the fact that the pi bond is slightly easier to break

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7
Q

What intermolecular forces of attraction do alkenes have?

A

Only london forces due to non polar bonds

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8
Q

Are they soluble in water?

A

No, non-polar bonds

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9
Q

Write an equation for the complete combustion of pent-2-ene

A

CH3CH=CHCH2CH3 + 7.5 O2 -> 5CO2 + 5H2O

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10
Q

What are the types of isomers that can be formed using alkenes

A

E/Z isomers - due to the restricted rotation

Cis-trans isomers - if two of the same substituents at=re attached to each carbon

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11
Q

What is an electrophile?

A

Species that are electron pair acceptors

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12
Q

What is the most stable type of carbocation intermediate? Why?

A

Alkyl groups have a positive inductive effect, so the most stable carbocation is the one bonded to the most other carbon atoms i.e. A tertiary carbocation

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13
Q

Major products will be formed from which kinds of carbocations?

A

Tertiary (or the most stable available)

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14
Q

What conditions are needed for the electrophilic addition of H2O to an alkene? What is this type of reaction called?

A

Steam in the presence of an acid catalyst, using phosphoric acid

Reaction is called hydration

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15
Q

What are the product (s) of the hydration reaction?

A

An alcohol

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16
Q

Draw a mechanism for the addition of water to ethene

A

mechanism

17
Q

What conditions are needed for the electrophillic addition of a hydrogen halide to an alkene?

A

Hydrogen halide gases must be at room temperature

18
Q

Draw a mechanism for the reaction of HBr and ethene

A

mechanism

19
Q

What is the reaction called when a halogen is added to alkene

A

Halogenation

20
Q

How does a molecule with a non-polar bond react as if it is an electrophile?

A

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule

Delta + atom attracted to double bond

21
Q

Draw a mechanism for the reaction between bromine and ethene

A

Mechanisms

22
Q

How can an alkene be converted into alkane?

What is the reaction called and what are the required conditions?

A

Alkene + hydrogen = alkane

Hydrogenation

Conditions = 150 degrees celcius and nickel catalyst

23
Q

What is an addition polymer?

A

Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule

24
Q

What are monomers?

What form do they usually take?

A

Molecules which combine to form a polymer

Usually have a C=C bond which breaks to leave a repeating pattern

25
Q

Draw how you would represent the polymerisation of ethene

A

polymerisation

26
Q

What are the ways in which plastics can be disposed? (6)

A
Landfill
Combustion
Electricity generation
Reuse
Recycle
Organic feedstock
27
Q

What are the disadvantaged of recycling?

A

Plastics must be sorted into different types
Expensive
Labour intensive
Requires high technology

28
Q

How does photodegradable polymers break down?

A

They are broken down chemically using energy with wavelengths similar to light.

Once the break down begins, it is to possible to stop the process

29
Q

Explain what happens in organic feedstock

A

Plastics are separated and broken down into small organic molecules through a series of reaction. The molecules can then be used to produce plastics and in other industries

30
Q

Give a disadvantage of photodegradable polymers

A

May not be exposed to sufficient light