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AH Chemistry > 3b- Synthesis > Flashcards

3b- Synthesis Flashcards

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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 are 3 key facts about about homolytic fission?

A
  • results in the formation of two neutral radicals
  • occurs when each atom retains one electron from the sigma covalent bond and
    the bond breaks evenly
  • normally occurs when non-polar covalent bonds are broken
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5
Q

What are 3 key facts about about heterolytic fission?

A
  • results in the formation of two oppositely charged ions
  • occurs when one atom retains both electrons from the sigma covalent bond and
    the bond breaks unevenly
  • normally occurs when polar covalent bonds are broken
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6
Q

What do reactions involving homolytic fusion tend to result in?

A

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

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7
Q

What do reactions involving heterolytic fusion tend to result in?

A

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

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8
Q

Which type of bond fission is better suited for organic synthesis?

A

Heterolytic fission

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9
Q

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

A

Using curly arrow notation

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10
Q

In reactions involving heterolytic bond fission, how are attacking groups classified?

A

Either as electrophiles or nucleophiles

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11
Q

What are nucleophiles?

A

Negatively charged ions or neutral molecules that are electron rich

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12
Q

What are examples of nucleophiles?

A 
Cl-
Br-
OH-
CN-
NH3
H2O
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13
Q

What are nucleophiles attracted towards?

A

Atoms bearing a partial or full positive charge

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14
Q

What are nucleophiles capable of doing?

A

Donating an electron pair to form a new covalent bond

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15
Q

What are electrophiles?

A

Positively charged ions or neutral molecules that are electron deficient

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16
Q

What are examples of electrophiles?

A

H+
NO2+
SO3

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17
Q

What are electrophiles attracted towards?

A

Atoms bearing a partial or full negative charge

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18
Q

What are electrophiles capable of doing?

A

Accepting an electron pair to form a new covalent bond

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19
Q

What are haloalkanes?

A

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

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20
Q

How many halogen atoms does a monohaloalkane have?

A

One

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21
Q

How can monohaloalkanes be classified?

A

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

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21
Q

How can monohaloalkanes be classified?

A

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

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22
Q

How can monohaloalkanes become alkenes?

A

Through elimination reactions using a strong base, such as, potassium or sodium hydroxide in ethanol

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23
Q

What are the 3 nucleophilic substitution reactions monohaloalkanes can undergo?

A
  • form alcohols with aqueous alkalis
  • form ethers with alcoholic alkoxides
  • form nitriles with ethanolic cyanide (chain length increased by 1 carbon atom),
    these nitriles can then be hydrolysed to carboxylic acids
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24
Q

What are the 2 mechanisms that monohaloalkanes can undergo nucleophilic substitution reactions by?

A
  • Sn1

- Sn2

25
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

26
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-centered, trigonal bipyramidial transition state

27
Q

What can be used to explain which mechanism (Sn1 or Sn2) will be preferred for a given haloalkane?

A

Steric hindrance and inductive stabilisation

28
Q

What are alcohols?

A

Substituted alkanes in which one or more of the hydrogen atoms is replaced by a hydroxyl functional group (-OH group)

29
Q

What are the 3 ways in which an alcohol can be prepared?

A
  • from haloalkanes by substitution
  • from alkenes by acid-catalysed hydration (addition)
  • from aldehydes and ketones by reduction using a reduction agent such as lithium
    aluminium hydride
30
Q

How can alcohols become alkenes?

A

Through dehydration reactions using aluminum oxide, concentrated sulfuric acid or concentrated phosphoric acid

31
Q

How can alcohols become aldehydes and then carboxylic acids?

A

Through oxidation of primary alcohols to form aldehydes and then further oxidation to form carboxylic acids

32
Q

How can alcohols form ketones?

A

Through oxidation of secondary alcohols to form ketones, using acidified potassium permanganate, acidified dichromate or hot copper (II) oxide

33
Q

How can alcohols become alcoholic alkoxides and then ethers?

A

By reaction with some reactive metals such as potassium or sodium. This alcoholic alkoxide can then be reacted with a monohaloalkane to form an ether

34
Q

What are the two ways in which an alcohol can form an ester, and which is the more effective way?

A
  • by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst
  • by reaction with acid chlorides

Using acid chlorides is more effective as it gives a faster reaction and does not require a catalyst

35
Q

What part of a alcohol makes it polar?

A

The hydroxyl group, which gives rise to hydrogen bonding

36
Q

What properties of alcohols can hydrogen bonding be used to explain?

A
  • boiling points
  • melting points
  • viscosity
  • miscibility in water
37
Q

What can ethers be regarded as?

A

Substituted alkanes in which a hydrogen atom is replaced with an alkoxy functional group (-OR group)

38
Q

How can ethers be prepared?

A

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

39
Q

Why do ether molecules have a low boiling point compared to corresponding isomeric alcohols?

A

Due to the lack of hydrogen bonding between ether molecules

40
Q

What are the two ethers which are soluble in water?

A
  • methoxymethane

- methoxyethane

41
Q

Why are larger ethers insoluble in water?

A

Due to their increased molecular size

42
Q

What are ethers commonly used as and why?

A

They are commonly used as solvents since they are relatively inert chemically and will dissolve many organic compounds

43
Q

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

A
  • dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
  • base-induced elimination of hydrogen halides from monohaloalkanes
44
Q

What are the 4 electrophilic addition reactions alkenes can take part in?

A
  • react with hydrogen to form alkanes in the presence of a catalyst
  • react with halogens to form dihaloalkanes
  • react with hydrogen halides to form monohaloalkanes
  • react with water using an acid catalyst to form alcohols
45
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

46
Q

What can Markovnikov’s rule be used to predict?

A

What the major and minor products formed during a reaction of a hydrogen halide or water with an alkene will be

47
Q

What are the 3 ways in which a carboxylic acid can 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 Tollen’s reagent
  • hydrolysing nitriles, esters or amines
48
Q

What are the 4 reactions that carboxylic acids can undergo?

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
49
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

50
Q

How can amines be classified?

A

A primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom

51
Q

What do amines form when they react with acids?

A

Salts

52
Q

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

A

Because primary and secondary amines display hydrogen bonding unlike tertiary amines

53
Q

All amines are soluble, however are long or short chain amines more soluble?

A

Short chain amines are more soluble

54
Q

How are amines similar to ammonia?

A

They are both 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

55
Q

What is benzene (C6H6)?

A

The simplest member of the class of aromatic hydrocarbons

56
Q

What is the stability of the benzene ring due to?

A

The delocalisation of electrons in the conjugated system. The presence of delocalised electrons explains why the benzene ring does not take part in addition reactions

57
Q

How can bonding in benzene be described in terms of?

A

sp2 hybridisation, sigma and pi bonds, and electron delocalisation

58
Q

What is a phenyl group?

A

A benzene ring in which one hydrogen atom has been substituted by another group. It has the formula C6H5-

59
Q

What type of reactions can benzene take part in?

A

Electrophilic substitution

60
Q

What are 4 electrophilic substitution reactions that benzene can undergo?

A
  • halogenation by reaction with 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

AH Chemistry (15 decks)

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