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AS Chemistry > 4.1.3 - Alkenes > Flashcards

4.1.3 - Alkenes Flashcards

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1
Q

What are stereoisomers?

A

Compounds with the same structural formula but with a different arrangement in space.

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2
Q

What is E/Z isomerism?

A

An example of stereoisomerism, in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group.

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3
Q

What is cis-trans isomerism?

A

A special case of E/Z isomerism in which two of the substituent groups are attached to each carbon atom of the C=C group are the same.

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4
Q

How do you know whether a compound is cis or trans?

A

When both hydrogens are on the same side of the double bond then the molecule is cis.

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5
Q

How can you work out whether something is an E or Z isomerism?

A

If the molecule with the highest atomic number on each side of the double bond is on the same side then it is Z.

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6
Q

How can you remember what Z and E mean?

A

Z = zusammen, E = entgehen.

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7
Q

General formula?

A

CnH2n

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8
Q

What are all alkenes?

A

Hydrocarbons which are unsaturated as they all contain at least one double bond.

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9
Q

What is a double bond made up of?

A

Sigma and pi bond.

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10
Q

When is a sigma bond formed?

A

When two s orbitals overlap.

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11
Q

How do s orbitals over lap?

A

In a straight line.

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12
Q

What does the overlapping of the s orbitals mean?

A

There is the highest possible electron density between the two nuclei.

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13
Q

What does high electron density lead to?

A

A strong electrostatic attraction between the nuclei and the shared pair of electrons.

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14
Q

Due to the strong electrostatic attraction is sigma bonds what does this lead to?

A

Sigma bonds having a high bond enthalpy.

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15
Q

How are pi bonds formed?

A

By the sideways overlap of two adjacent p orbitals.

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16
Q

Why are pi bonds much weaker than sigma bonds?

A

The electron density is spread out above and below the nuclei. Therefore the electrostatic attraction between the nuclei and the shared pair of electrons is weaker.

17
Q

Why do pi bonds have relatively low bond enthalpy?

A

The electrostatic attraction between the nuclei and the shared pair of electrons is weaker.

18
Q

Why can’t C=C bonds rotate?

A

Because of the way the p orbitals overlap to form a pi bond.

19
Q

What is the shape and bond angle of alkenes?

A

Trigonal planar and 120 degrees.

20
Q

How can waste polymers be reused?

A

They can be combusted, turned into organic feedstock or melted and remoulded.

21
Q

Why can waste polymers be combusted?

A

They have a high calorific value, so when burnt in power stations the chemical energy transferred can be used to drive turbines and generate electricity.

22
Q

What are the conditions needed for hydrogenation?

A

150 degrees C and nickel catalyst.

23
Q

What is added in hydrogenation?

A

Hydrogen.

24
Q

What is added in halogenation?

A

A halogen such as Br2 or Cl2.

25
Q

What is test for alkenes?

A

Shake bromine water with an alkene. The solution will turn colourless.

26
Q

What kind of mechanisms are halogenation and hydrogenation?

A

Electrophilic addition.

27
Q

What are electrophiles?

A

Electron pair acceptors.

28
Q

What is added during hydration.

A

Steam

29
Q

What are the conditions for hydration?

A

H3PO4 catalyst, 65atm and 300 degrees C.

30
Q

What are the conditions for hydrohalogenation?

A

Room temperature.

31
Q

What is produced in hydrohalogenation?

A

More than 1 product, a minor and a major one.

32
Q

How can you tell which product is major?

A

The one with the larger carbocation.

33
Q

What is a tertiary carbocation?

A

More stable than primary and secondary and it is connected to three other carbons and then the cation.

AS Chemistry (24 decks)

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