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Chemistry A-level > Chapter 13 > Flashcards

Chapter 13 Flashcards

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1
Q

What is the definition of a alkene?

A

Alkenes are unsaturated hydrocarbons which contain C=C double bond comprising of a pie bond and a sigma bond.

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2
Q

What is a pie bond?

A

A pie bond is the sideways overlap of adjacent p-orbitals above and below the bonding atoms.

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3
Q

What is a sigma bond?

A

A sigma bond is the overlap of orbitals directly between the bonding atoms.

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4
Q

What is the shape and bond angle of alkenes? why?

A

It is a trigonal planar and a bond angle of 120 because there are three pairs of electrons which repel each other as far as possible around the central atom.

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5
Q

What are stereoisomerisms?

A

A stereoisomerism are compounds with the same molecular and structural formula, but with a different arrangement of atoms in space.

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6
Q

What are E/Z stereoisomerisms?

A

E/Z stereoisomerisms is an example of stereoisomerisms, this arises due to the restricted rotation about the double bond, when there is two different groups attached to each carbon atom in the bond.

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7
Q

What allows for stereoisomerisms?

A

Restricted rotation of the pie-bond.

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8
Q

What are cis-trans isomerism?

A

A special case of E/Z isomerism where 2 groups are attached to each carbon of the double bond.

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9
Q

How to work out E/Z stereoisomerisms?

A

1) Draw the alkene with the C=C bond at the centre of the molecule.
2) Determine the highest priority substituent on the 1st C=C carbon. The substituent with the greater atomic number is the highest priority.
3) Repeat for the 2nd C=C.
4) If the highest priority substituents are on the same side, it is z-isomer.
5) If the highest priority substituents are on opposite sides, it is E-isomer.

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10
Q

Where are the highest priority substituents on the Z-isomer?

A

The highest priority substituents are on the same side, it is z-isomer.

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11
Q

Where are the highest priority substituents on the e-isomer?

A

the highest priority substituents are on opposite sides, it is E-isomer.

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12
Q

What is the trans-isomer?

A

The same groups are on opposite sides of the bond.

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13
Q

What is the cis-isomer

A

The same groups are on one side of the bond.

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14
Q

What is the reactivity of alkenes? why?

A

The alkenes are relativity reactive because the pie bond is a region of high electron density, and has a relative bond enthalpy.

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15
Q

What are the four examples of alkene addition reactions?

A
  • hydrogen in the presence of a nickel catalyst
  • halogens
  • hydrogen halides
  • stem in the presence of an acid catalyst.
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16
Q

What is hydrogenation of alkenes?

A

When an alkene is mixed with hydrogen and passed over a nickel catalyst, an addition reaction takes to form an alkane. This addition reaction, in which hydrogen is added across a double bond.

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17
Q

What is halogenation of alkanes?

A

Alkanes undergo a rapid addition reaction with halogens chlorine or bromine to form dihaloalkanes at room temperature. The mechanism is electrophilic addition and the type of bond fission is heterolytic.

18
Q

What mechanism is halogenation of alkanes?

A

Electrophilic addition.

19
Q

What bond fission is halogenation of alkanes?

A

Heterolytic

20
Q

How do you test for a C=C bond?

A

Add bromine dropwise. The orange colour will decolourises which indicates a C=C bond.

21
Q

What is the reaction of alkenes with hydrogen halides?

A

Alkenes react with gaseous hydrogen halides at room temperature to form haloalkanes. Alkenes also react with concentration hydrochloric or hydrobromic
acid.

22
Q

What is mechanism for reaction of alkenes with hydrogen halides?

A

Electrophilic addition.

23
Q

What is an hydration reaction of alkenes.

A

Alkenes react with steam, H2O(g), in the presence of a phosphoric acid catalyst, H3PO4, to form alcohols. This reaction produces a 100% atom economy.

24
Q

What is the definition of an electrophile?

A

Electrophilic are electron pair acceptors attracted to high areas of density.

25
Q

What is the electrophilic mechanism?

A

The electron pair in the π-bond is attracted to the partially positive hydrogen atom, causing the double
bond to break. The H-Br bond breaks by
heterolytic fission, with the electron pair going to
the bromine atom. Bromine is more
electronegative than hydrogen, so hydrogen
bromide is polar. HBr = the electrophile. A bromide ion and a carbocation intermediate form. The bromide ion reacts with the carbocation to form the
addition product.

26
Q

What is a carbocation?

A

It contains a positively charged atom.

27
Q

What happen if the akene is unsymmetrical when electrophilic addition happens?

A

Then more than one product can be formed.

28
Q

What is Markownikoff’s rule?

A

The major product forms via the most stable carbocation intermediate. Tertiary carbocation are the most stable then secondary carbocation then primary carbocation- least stable.

29
Q

What are addition polymers?

A

Addition polymers are saturated chains formed from alkene molecules.

30
Q

How are addition polymers named?

A

They are named by placing ‘poly’ in front of the monomer name in brackets.

31
Q

What is a repeat unit of a polymer?

A

It is the set of atoms that are joined together in larger numbers to produce the polymer structure.

32
Q

What is n?

A

The n is the repeating unit represents the no. of monomers.

33
Q

What is recycling?

A

Recycling polymer waster can conserve natural resources. The polymer is tediously and inefficiently sorted before being processed and used to make new materials.

34
Q

What is a promblem with recycling?

A

Some polymers, including PVC are particularly difficult to recycle as the toxic and corrosive additions first need to be removed.

35
Q

What is incineration?

A

The polymer waste is combusted to convert it into heat energy for use in electricity generation.

36
Q

What is the problem with incineration?

A

Incineration can produce toxic gases, e.g HCL which can be removed from incinerator chimneys.

37
Q

What is organic feedstock?

A

The polymer waste is broken down into gases, mainly H2 and CO, or oil. These can be used in other chemical reactions, such as cracking, or as raw materials for new plastics and other chemicals.

38
Q

What is a biodegradable polymer?

A

It is plant-based and can be broken down by microbes.

39
Q

What is a biodegradable polymer?

A

It is oil-based, but can be broken down by absorbing light.

40
Q

What is the benefit of a biodegradable polymer and a biodegradable polymer?

A

These both provide provide renewable and sustainable alternatives to reduce oil use and reduce water.

Chemistry A-level (14 decks)

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