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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
What are electrophiles attracted towards?
Atoms bearing a partial or full negative charge.
26
What are electrophiles capable of?
Accepting an electron pair to form a new covalent bond.
27
What can synthetic routes be devised from, with no more than three steps?
A given reactant to a final product.
28
How can the possible reactions of a particular molecule be deduced?
By looking at the structural formula.
29
What is in a skeletal structural formula?
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.
30
What are haloalkanes (alkyl halides)?
Substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom.
31
What do monohaloalkanes contain?
Only one halogen atom.
32
How can monohaloalkanes be classified?
As primary, secondary or tertiary according to the number of alkyl groups attached to the carbon containing the halogen atom.
33
What do monohaloalkanes take part in to form?
Elimination reactions to form alkenes using a strong base, such as sodium or potassium hydroxide in ethanol.
34
What do monohaloalkanes also take part in?
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
What two different mechanisms can monohaloalkanes take part in nucleophilic substitution reactions by?
SN1 or SN2.
36
What is SN1?
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
What is SN2?
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
How can the reaction mechanisms for SN1 and SN2 reactions be represented?
Using curly arrows.
39
What can be used to explain which mechanism will be preferred for a given haloalkane?
Steric hinderance and the inductive stabilisation of the carbocation intermediate.
40
What are alcohols?
Substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl functional group, –OH group.
41
What can alcohols be prepared from?
Haloalkanes by substitution; Alkenes by acid-catalysed hydration (addition); Aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride.
42
What does the dehydration of alcohols form?
Alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid.
43
What does oxidation of primary alcohols form?
Aldehydes and then carboxylic acids.
44
What does oxidation of secondary alcohols form?
Ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide.
45
How do you form alcoholic alkoxides?
Alcohols react with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers.
46
How do you form esters?
Alcohols reacting with carboxylic acids using concentrated sulphuric acid or concentrated phosphoric acid as a catalyst.
47
How else can you form esters with alcohols?
By reaction with acid chlorides — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed.
48
What can ethers be regarded as?
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
How are ethers named?
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
How can ethers be prepared?
In a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide.
51
What do ethers have due to the lack of hydrogen bonding between ether molecules?
They have lower boiling points than the corresponding isomeric alcohols.
52
Which ethers are soluble in water?
Methoxymethane and methoxyethane.
53
Why are ethers commonly used as solvents?
Since they are relatively inert chemically and will dissolve in many organic compounds.
54
Why are larger ethers insoluble in water?
Due to their increased molecular size.
55
Which two ways can alkenes be prepared?
By: Dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid; Base-induced elimination of hydrogen halides from monohaloalkanes.
56
What do alkenes take part in electrophilic addition reactions with?
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
What does Markovnikov's rule state?
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
What can Markovnikov's rule be used for?
To predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes.
59
How can the reaction mechanisms for the addition of a hydrogen halide and the acid-catalysed addition of water be represented?
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
How can the reaction mechanism for the addition of a halogen be represented?
Using curly arrows and showing the cyclic ion intermediate.
61
How can carboxylic acids be prepared?
 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
What do reactions of carboxylic acids include?
 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
What are amines?
Organic derivatives of ammonia in which one or more hydrogen atoms of ammonia has been replaced by an alkyl group
64
What can amines be classified as?
Primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom.
65
What do amines react with acids to form?
Salts.
66
Why do primary and secondary amines have higher boiling points than isometric tertiary amines?
Primary and secondary amines, but not tertiary amines, display hydrogen bonding.
67
What explains the appreciable solubility of the shorter chain length amines in water?
Primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules.
68
What are amines like ammonia?
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
What is benzene (C6H6)?
The simplest member of the class of aromatic hydrocarbons.
70
What does the benzene ring have?
A distinctive structural formula.
71
What is the stability of the benzene ring due to?
The delocalisation of electrons in the conjugated system.
72
What does the presence of delocalised electrons in the benzene ring explain?
Why the benzene ring does not take part in addition reactions.
73
What can bonding in benzene be described in terms of?
Sp2 hybridisation, sigma and pi bonds, and electron delocalisation.
74
What is the phenyl group?
A benzene ring in which one hydrogen atom has been substituted by another group.
75
What does the phenyl group have the formula?
-C6H5.
76
What can benzene rings take part in?
Electrophilic substitution reactions.
77
What do reactions at benzene rings include?
 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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