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chemistry - 4.2 Flashcards

1
Q

What happens when an organic reaction takes place?

A

Bonds in the reactant molecules are broken and bonds in the product molecules are made.

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2
Q

What is the process of bond breaking known as?

A

Bond fission.

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3
Q

What are the two types of bond fission?

A

Homolytic and heterolytic.

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4
Q

What does homolytic fission result in?

A

The formation of two neutral radicals.

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5
Q

When does homolytic fission occur?

A

When each atom retains one electron from the sigma covalent bond and the bond breaks evenly.

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6
Q

When does homolytic fission normally occur?

A

When non-polar covalent bonds are broken.

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7
Q

What do reactions involving homiletic fission tend to result in?

A

The formation of very complex mixtures of products, making them unsuitable for organic synthesis.

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8
Q

What does heterolytic fission result in?

A

The formation of two oppositely charged ions.

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9
Q

When does heterolytic fission occur?

A

When one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly.

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10
Q

When does heterolytic fission normally occur?

A

When polar covalent bonds are broken.

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11
Q

What do reactions involving heterolytic fission tend to result in?

A

Far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis.

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12
Q

How can the movement of electrons during bond fission and bond making be represented?

A

Using curly arrow notation.

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13
Q

What does a single-headed arrow indicate?

A

The movement of a single electron.

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14
Q

What does a double-headed arrow indicate?

A

The movement of an electron pair.

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15
Q

What does the tail of the arrow show?

A

The source of the electron(s).

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16
Q

What does the head of the arrow indicate?

A

The destination of the electron(s).

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17
Q

What do two single-headed arrows starting at the middle of a covalent bond indicate?

A

Homolytic bond fission is occurring.

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18
Q

What does a double-headed arrow starting at the middle of a covalent bond indicate?

A

Heterolytic bond fission is occurring.

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19
Q

What does an arrow drawn with the head pointing to the space between two atoms indicate?

A

That a covalent bond will be formed between those two atoms.

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20
Q

In reaction involving heterolytic bond fission, what are attacking groups classified as?

A

Nucleophiles or electrophiles.

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21
Q

What are nucleophiles?

A

Negatively charged ions or neutral molecules that are electron rich, such as Cl−, Br−, OH−, CN− , NH3 and H2O.

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22
Q

What are nucleophiles attracted towards?

A

Atoms bearing a partial or full positive charge.

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23
Q

What are nucleophiles capable of?

A

Donating an electron pair to form a new covalent bond.

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24
Q

What are electrophiles?

A

Positively charged ions or neutral molecules that are electron deficient, such as
H+,NO+ and SO3.

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25
Q

What are electrophiles attracted towards?

A

Atoms bearing a partial or full negative charge.

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26
Q

What are electrophiles capable of?

A

Accepting an electron pair to form a new covalent bond.

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27
Q

What can synthetic routes be devised from, with no more than three steps?

A

A given reactant to a final product.

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28
Q

How can the possible reactions of a particular molecule be deduced?

A

By looking at the structural formula.

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29
Q

What is in a skeletal structural formula?

A

Neither the carbon atoms, nor any hydrogens attached to the carbon atoms, are shown. The presence of a carbon atom is implied by a ‘kink’ in the carbon backbone, and at the end of a line.

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30
Q

What are haloalkanes (alkyl halides)?

A

Substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom.

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31
Q

What do monohaloalkanes contain?

A

Only one halogen atom.

32
Q

How can monohaloalkanes be classified?

A

As primary, secondary or tertiary according to the number of alkyl groups attached to the carbon containing the halogen atom.

33
Q

What do monohaloalkanes take part in to form?

A

Elimination reactions to form alkenes using a strong base, such as sodium or potassium hydroxide in ethanol.

34
Q

What do monohaloalkanes also take part in?

A

Nucleophilic substitution reactions with:
— aqueous alkalis to form alcohols
— alcoholic alkoxides to form ethers
— ethanolic cyanide to form nitriles (chain length increased by one carbon atom) that can be hydrolysed to carboxylic acids.

35
Q

What two different mechanisms can monohaloalkanes take part in nucleophilic substitution reactions by?

A

SN1 or SN2.

36
Q

What is SN1?

A

A nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate.

37
Q

What is SN2?

A

A nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state.

38
Q

How can the reaction mechanisms for SN1 and SN2 reactions be represented?

A

Using curly arrows.

39
Q

What can be used to explain which mechanism will be preferred for a given haloalkane?

A

Steric hinderance and the inductive stabilisation of the carbocation intermediate.

40
Q

What are alcohols?

A

Substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl functional group, –OH group.

41
Q

What can alcohols be prepared from?

A

Haloalkanes by substitution;
Alkenes by acid-catalysed hydration (addition);
Aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride.

42
Q

What does the dehydration of alcohols form?

A

Alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid.

43
Q

What does oxidation of primary alcohols form?

A

Aldehydes and then carboxylic acids.

44
Q

What does oxidation of secondary alcohols form?

A

Ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide.

45
Q

How do you form alcoholic alkoxides?

A

Alcohols react with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers.

46
Q

How do you form esters?

A

Alcohols reacting with carboxylic acids using concentrated sulphuric acid or concentrated phosphoric acid as a catalyst.

47
Q

How else can you form esters with alcohols?

A

By reaction with acid chlorides — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed.

48
Q

What can ethers be regarded as?

A

Substituted alkanes in which a hydrogen atom is replaced with an alkoxy functional group, –OR, and have the general structure R’ – O – R’’, where R’ and R’’ are alkyl groups.

49
Q

How are ethers named?

A

As substituted alkanes. The alkoxy group is named by adding the ending ‘oxy’ to the alkyl substituent, and this prefixes the name of the longest carbon chain.

50
Q

How can ethers be prepared?

A

In a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide.

51
Q

What do ethers have due to the lack of hydrogen bonding between ether molecules?

A

They have lower boiling points than the corresponding isomeric alcohols.

52
Q

Which ethers are soluble in water?

A

Methoxymethane and methoxyethane.

53
Q

Why are ethers commonly used as solvents?

A

Since they are relatively inert chemically and will dissolve in many organic compounds.

54
Q

Why are larger ethers insoluble in water?

A

Due to their increased molecular size.

55
Q

Which two ways can alkenes be prepared?

A

By:
Dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid;
Base-induced elimination of hydrogen halides from monohaloalkanes.

56
Q

What do alkenes take part in electrophilic addition reactions with?

A

Hydrogen to form alkanes in the presence of a catalyst;
Halogens to form dihaloalkanes;
Hydrogen halides to form monohaloalkanes;
Water using an acid catalyst to form alcohols.

57
Q

What does Markovnikov’s rule state?

A

That when a hydrogen halide or water is added to an unsymmetrical alkene, the hydrogen atom becomes attached to the carbon with the most hydrogen atoms attached to it already.

58
Q

What can Markovnikov’s rule be used for?

A

To predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes.

59
Q

How can the reaction mechanisms for the addition of a hydrogen halide and the acid-catalysed addition of water be represented?

A

Using curly arrows and showing the intermediate carbocation. The inductive stabilisation of intermediate carbocations formed during these reactions can be used to explain the products formed.

60
Q

How can the reaction mechanism for the addition of a halogen be represented?

A

Using curly arrows and showing the cyclic ion intermediate.

61
Q

How can carboxylic acids be prepared?

A

 oxidising primary alcohols using acidified permanganate, acidified dichromate and hot copper(II) oxide
 oxidising aldehydes using acidified permanganate, acidified dichromate, Fehling’s solution and Tollens’ reagent
 hydrolysing nitriles, esters or amides

62
Q

What do reactions of carboxylic acids include?

A

 formation of salts by reactions with metals or bases
 condensation reactions with alcohols to form esters in the presence of concentrated sulfuric or concentrated phosphoric acid
 reaction with amines to form alkylammonium salts that form amides when heated
 reduction with lithium aluminium hydride to form primary alcohols

63
Q

What are amines?

A

Organic derivatives of ammonia in which one or more hydrogen atoms of ammonia has been replaced by an alkyl group

64
Q

What can amines be classified as?

A

Primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom.

65
Q

What do amines react with acids to form?

A

Salts.

66
Q

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

A

Primary and secondary amines, but not tertiary amines, display hydrogen bonding.

67
Q

What explains the appreciable solubility of the shorter chain length amines in water?

A

Primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules.

68
Q

What are amines like ammonia?

A

Weak bases and dissociate to a slight extent in aqueous solution. The nitrogen atom has a lone pair of electrons which can accept a proton from water, producing hydroxide ions.

69
Q

What is benzene (C6H6)?

A

The simplest member of the class of aromatic hydrocarbons.

70
Q

What does the benzene ring have?

A

A distinctive structural formula.

71
Q

What is the stability of the benzene ring due to?

A

The delocalisation of electrons in the conjugated system.

72
Q

What does the presence of delocalised electrons in the benzene ring explain?

A

Why the benzene ring does not take part in addition reactions.

73
Q

What can bonding in benzene be described in terms of?

A

Sp2 hybridisation, sigma and pi bonds, and electron delocalisation.

74
Q

What is the phenyl group?

A

A benzene ring in which one hydrogen atom has been substituted by another group.

75
Q

What does the phenyl group have the formula?

A

-C6H5.

76
Q

What can benzene rings take part in?

A

Electrophilic substitution reactions.

77
Q

What do reactions at benzene rings include?

A

 halogenation by reaction of a halogen using aluminium chloride or iron(III) chloride for chlorination and aluminium bromide or iron(III) bromide for bromination
 alkylation by reaction of a haloalkane using aluminium chloride
 nitration using concentrated sulfuric acid and concentrated nitric
acid
 sulfonation using concentrated sulfuric acid

advanced higher chemistry (36 decks)

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