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CfE Advanced Higher Chemistry > Synthesis of Aliphatic Molecules (U2,c4/6) > Flashcards

Synthesis of Aliphatic Molecules (U2,c4/6) Flashcards

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1
Q

Why are alkanes not particularly reactive?

A

Their bonds are non-polar.

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2
Q

Under what circumstances can alkanes react with halogens?

A

In the presence of UV light.

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3
Q

What are the three steps in a halogen + alkane chain reaction?

A

Propagation, initiation and termination.

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4
Q

What is homolytic fission?

A

When the bond splits evenly - the same thing happens to both atoms (one electron from the bond goes to one atom, and the other electron goes to the other atom)

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5
Q

What is heterolytic fission?

A

When the bond splits UNevenly - a different thing happens to each atom (one atom gets both electrons and the other gets none)

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6
Q

What are produced by homolytic fission?

A

Free radicals

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7
Q

What are produced by heterolytic fission?

A

Ions

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8
Q

What is an electrophile?

A

Electron-dependant species. Molecules or +ve ions that can accept an electron pair.

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9
Q

What is a nucleophile?

A

Electron-rich species. Molecules or -ve ions that can donate an electron pair.

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10
Q

What is a dative covalent bond?

A

A covalent bond in which Bothe electrons are supplied by the same atom (as in heterolytic fission)

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11
Q

What does a single-headed curly arrow indicate?

A

Movement of a single electron (radical chemistry mechanisms)

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12
Q

What does a double-headed curly arrow indicate?

A

Movement of an electron pair.

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13
Q

What would a curly arrow starting in the middle of a covalent bond indicate?

A

Heterolytic fission is occurring.

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14
Q

What would a curly arrow with the head pointing to a space between two atoms indicate?

A

A covalent bond is being formed between the two atoms.

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15
Q

What forms when an halogenoalkane reacts with an alkali (under reflux)?

What is the nucleophile here?

A

An alcohol.

OH- is the nucleophile.

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16
Q

What forms when an halogenoalkane reacts with an alcoholic alkoxide?

What is the nucleophile here?

A

An ether.

Oxide is the nucleophile.

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17
Q

What forms when an halogenoalkane reacts with ethanoic potassium/sodium cyanide?

What is the nucleophile here?

A

A nitrile.

Cyanide ion (CN) is the nucleophile.

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18
Q

Why is a monohaloalkane reacting with ETHANOLIC potassium//sodium hydroxide different from that with AQUEOUS potassium//sodium hydroxide.

A

The ethanolic solution causes an ELIMINATION reaction to occur, while the aqueous one causes a nucleophilic substitution.

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19
Q

What are the 3 different structural types of Monohaloalkane?

A

Primary, secondary and tertiary.

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20
Q

What are haloalkanes?

A

Subtituted alkanes - where one or more of the hydrogen atoms have been replaced by a halogen atom.

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21
Q

What are the two mechanisms by which a haloalkane undergoes a nucleophilic substitution called?

A

SN1 and SN2.

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22
Q

In an SN1 mechanism, what species is/are involved in the rate-determining step (RDS)?

A

Only the haloalkane

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23
Q

In an SN2 mechanism, what species is/are involved in the rate-determining step (RDS)?

A

Both the haloalkane and the nucleophile.

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24
Q

How many steps are in a SN1 process?

A

Two.

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25
Q

How many steps are in a SN2 process?

A

One.

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26
Q

How do you know which reaction mechanism (SN1 or SN2) a haloalkane will undergo?

A

By looking at what type of haloalkane - primary, secondary or tertiary - you’re dealing with.

27
Q

Describe an SN1 reaction.

A

Step 1 (SLOW): A carbocation (positively charged) intermediate is formed. Step 2 (FAST - RDS): The nucleophile donated electrons to the carbocation.

28
Q

Describe an SN2 reaction.

A

The nucleophile attacks the slightly positive carbon atom, and forms a negative intermediate (transition state), with the halogen ion being removed in the final product (all ONE STEP).

29
Q

How does the boiling point of an alcohol compare to that of a similar alkane? Why?

A

The alcohol’s boiling point is considerably higher, due to hydrogen bonding between molecules because of the OH group.

30
Q

What happens to alcohol boiling point as chain length increases?

A

Boiling point increases.

31
Q

What happens to alcohol solubility as chain length increases?

A

Solubility decreases.

32
Q

Why are shorter chain alcohols soluble in water?

A

The energy released in FORMING H bonds between the alcohol & water molecules is enough to BREAK H bonds between the water molecules. If the chain is too long, it disrupts the H bonding ability between the water and OH.

33
Q

What are the two ways in which alcohols can be prepared?

A
  1. Heating Haloalkanes under reflux with aqueous Na/K Hydroxide (nucleophilic substitution).
  2. Acid catalysed hydration of Alkenes via a carbocation intermediate (addition of water).
34
Q

PART 1:
What is the electrophile in the acid catalysed hydration of alkenes to form alcohols?
What electrons attack it?
What is formed as a consequence?

PART 2:
The carbocation is attacked by a nucleophile. What is the nucleophile?
What is then formed?
What happens next to form the product?

A

PART 1:
The H ion of the acid catalyst.
The electrons of the (electron-rich) double bond attack it. A carbocation (+ve) is formed.

PART 2:
A water molecule.
A protonated alcohol.
The protonated alcohol is a strong acid, and readily loses a proton to give the final product.

35
Q

What is an alkoxide?

A

An alikali metal added to an alcohol.

36
Q

What are the two ways in which alcohols can be dehydrated?

A
  1. Passing the alcohol vapour over hot aluminium oxide.

2. Treating the alcohol with concentrated sulfuric/(ortho)phosphoric acid.

37
Q

What is formed when an alcohol reacts with a carboxylic acid OR acid chloride?
What kind of reaction is this?
What catalyst is used (carboxylic acid only)?

A

An ester.
Condensation / esterification.
Concentrated sulphuric acid.

38
Q

What is formed when an aldehyde is reduced with an aluminium hydride/sodium borohydride catalyst?

A

A primary alcohol.

39
Q

What is formed when a ketone is reduced with an aluminium hydride/sodium borohydride catalyst?

A

A secondary alcohol.

40
Q

What is formed when a primary alcohol is slightly oxidised?

What catalyst is used?

A

An aldehyde.

The catalyst is hot copper (II) oxide or acidified potassium dichromate.

41
Q

What is formed when a secondary alcohol is slightly oxidised?
What catalyst is used?

A

A ketone.

The catalyst is hot copper (II) oxide or acidified potassium dichromate.

42
Q

What kind of substances are alcohol hydroxyl groups found in? Why?

A

Pharmaceutical drugs.

They are involved in H bonding at protein binding sites.

43
Q

What two species can ethers be synthesised from?

A

Haloalkanes and alkoxides.

44
Q

How do the boiling points of ethers compare to those of their isomeric alcohols?
Why is this?

A

They are much lower…

…since there are no OH groups, and therefore no H bonding BETWEEN molecules.

45
Q

Why are smaller ethers soluble in water?

A

H bonds can form between the ether and water molecules.

46
Q

What are the two ways in which alkenes can be prepared?

A
  1. Dehydrating alcohols with aluminium oxide or conc. sulphuric/orthophosphoric acid.
  2. Eliminating hydrogen halides from monohaloalkanes (base-induced).
47
Q

Decribe the two-step mechanism for alkene halogenation (addition of halogens).

A

STEP 1:
The halogen approaches the double bond and becomes polarised, the (e.g.) Br-Br bond breaking heterolytically, creating a cyclic intermediate (+ve with halogen atom attached) and a halide ion.

STEP 2:
The halide ion acts as a nucleophile attacks from the OPPOSITE side of the halogen atom, forming the haloalkane.

48
Q

Decribe the two-step mechanism for alkene hydrohalogenation (addition of hydrogen halides).

A

STEP 1:
The hydrogen halide is already polarised. The electrons of the double bond attack the hydrogen, the (e.g.) H-Br bond breaking heterolytically, creating a halide ion and a carbocation (since the C=C bond breaks and bonds with the H).

STEP 2:
The halide ion attacks the carbocation from either side, forming the product.

49
Q

Decribe the three-step mechanism for alkene hydration (addition of water).

A
  1. The +ve carbocation is formed (H+ lost)
  2. The carbocation undergoes nucleophilic attack by a water molecule to give a protonated alcohol.
  3. The protonated alcohol, which is a strong acid, loses a proton to give the final alcohol.
50
Q

What is Markovnikov’s Rule?

A

When H-X is added onto an unsymmetrical alkene, the MAJOR product is the one where the hydrogen bonds to the carbon atom of the C=C bond that already has the greatest number of H atoms attached to it.

51
Q

What are the two ways in which carboxylic acids can be prepared?

A
  1. Oxidising primary alcohols/aldehydes by heating them with acidified potassium dichromate.
  2. Hydrolysing nitriles, esters or amides by heating them with an acid OR alkali catalyst.
52
Q

How do boiling points of carboxylic acids compare with those of similar alkanes?
Why is this?

A

Boiling points are considerably higher…

…due to H bonds BETWEEN the molecules.

53
Q

What is a dimer?

A

A molecule or molecular complex consisting of two identical molecules linked together.

54
Q

What is a dimer?

A

A molecule or molecular complex consisting of TWO identical molecules linked together.

55
Q

Why are smaller carboxylic acids soluble in water?

A

H bonds can form between the carboxylic acid and water molecules.

56
Q

What is produced when a carboxylic acid reacts with a amine?

A

An amide.

57
Q

What is produced when a carboxylic acid reacts with a metal?

A

A salt and hydrogen gas.

58
Q

What is produced when a carboxylic acid reacts with a metal carbonate?

A

A salt, water and carbon dioxide gas.

59
Q

What are the 3 different structural types of Monohaloalkane?

A

Primary, secondary and tertiary.

60
Q

From where are amines derived?

A

From ammonia, where one or more Hs have been replaced with an alkyl group.

61
Q

Why do primary and secondary amines have higher boiling points than tertiary amines?

A

H bonding only occurs between primary and secondary amines, but not tertiary amines, due to no Hs being directly attached to the highly electronegative N atom.

62
Q

Why are ALL amines soluble in water?

A

They can all form H bonds with water molecules.

63
Q

What is produced when amines react with hydrochloric/sulphuric/nitric acid?

A

A salt is formed.

64
Q

What is produced when amines react with a carboxylic acid?

What is then formed when the product is heated?

A

A salt is formed.

Amides are then produced when the salt is heated, as it loses water.

CfE Advanced Higher Chemistry (7 decks)

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