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AH Chemistry > 3.2 synthesis > Flashcards

3.2 synthesis Flashcards

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1
Q

what happens to the bonds in the reactant molecules when an organic reaction takes place

A

they are broken and bonds in the product molecules are made

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2
Q

what is bond fission

A

the process of bond breaking

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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 is homolytic fission

A

this is when the electrons are separated equally, forming two neutral radicals

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5
Q

what occurs during homolytic fission

A

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 usually occurs

A

when non polar covalent bonds are broken

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7
Q

what do reactions involving homolytic fission tend to result in the formation of

A

a very complex mixture of products, making them unsuitable for organic synthesis

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8
Q

what does heterolytic fission form

A

two oppositely charged ions

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9
Q

when does heterolytic fission form

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 occur in relation to bonds

A

when polar covalent bonds are broken

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11
Q

what can be used to represent the movement of electrons during bond fission and bond making

A

curly arrow notation

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12
Q

what are attacking groups classified as in reactions involving heterolytic bond fission

A

nucleophiles or electrophiles

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13
Q

what are nucleophiles

A

negatively charged ions or neutral molecules that are electron rich, and they are attracted toward atoms bearing a partial or full positive charge. they are capable of donating an electron pair to form a new covalent bond

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14
Q

what are electrophiles

A

these are positively charged ions or neutral molecules that are electron deficient, and they are attracted toward atoms bearing a partial or full negative charge. they are capable of accepting an electron pair to form a new covalent bond

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15
Q

which reaction types can be identified from a chemical equation

A

substitution
addition
elimination
condensation
hydrolysis
oxidation
reduction
neutralisation

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16
Q

how can synthetic routes be devised

A

from a given reactant to final product

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17
Q

what can be deduced by looking at the structural formula

A

the possible reactions of a particular molecule

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18
Q

what is skeletal structural formula

A

neither the carbon atoms or any hydrogen 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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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

what is a monohaloalkane

A

these contain only one halogen atom, can be classified 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

what do monohaloalkanes take part in elimination reactions to form

A

alkenes using a strong base, such as potassium, or sodium hydroxide in ethanol.

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22
Q

what are the nucleophilic substitution reactions that monohaloalkanes take part in

A
  • aqueous alkalis to form alcohols
  • alcoholic alkoxides to form ethers
  • ethanoic cyanide to form nitriles that can be hydrolysed to carboxylic acids
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23
Q

what are the different mechanisms that monohaloalkanes can take part in nucleophilic substitution reactions by

A

Sn1 and Sn2

24
Q

what is the Sn1 mechanism

A

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

25
Q

what is the Sn2 mechanism

A

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

26
Q

what is a steric hindrance

A

the slowing of chemical reactions due to steric bulk. steric iss the arrangement of atoms in space

27
Q

what is inductive stabilisation

A

the stability of a molecule depending on the charge present on the atom and the groups bonded to the atom

28
Q

how can alcohols be prepared

A

from haloalkanes by substitution
from alkenes by acid catalysed hydration
aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride

29
Q
A
30
Q

what makes alcohols polar

A

the hydroxyl groups

31
Q

what are ethers regarded as

A

substituted alkanes in which a hydrogen atom is replaced by an alkoxy functional group

32
Q

what is the alkoxy functional group

A

-OR

33
Q

how can ethers be prepared

A

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

34
Q

why do ethers have lower boiling points than the corresponding isomeric alcohols

A

due to the lack of hydrogen bonding between the molecules

35
Q

why are larger ethers insoluble in water

A

due to their increased molecular size

36
Q

what are examples of soluble ethers

A

methoxymethane and methoxyethane

37
Q

why are ethers commonly used as solvents

A

they are relatively inert chemically and will dissolve many organic compounds

38
Q

how can alkenes be prepared

A
  • dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
  • base induced elimination of hydrogen halides from monohaloalkanes
39
Q

what are the electrophilic addition reactions that alkenes take part 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

40
Q

what does markovnikov’s rule state

A

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. this rule can be used to predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes

41
Q

how can carboxylic acids be prepared

A

by oxidising primary alcohols using acidified permangenate, acidified dichromate, fehling’s solution and tollen’s reagent
hydrolysing nitriles, esters or amides

42
Q

what are examples of reactions involving carboxylic acids

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
43
Q

what are amines

A

organic derivatives of ammonia in which one of more hydrogen atoms of ammonia has been replaced by an alkyl group. they can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom

44
Q

what do amines react with the form salts

A

acids

45
Q

which type of amines display hydrogen bonding

A

primary and secondary

46
Q

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

A

they display hydrogen bonding

47
Q

are amines weak bases, and what does this imply

A

yes, and it means they dissociate partially in solution.

48
Q

how do amines produce hydroxide ions

A

the nitrogen atom has a lone pair of electrons which can accept a proton from water

49
Q

what is the simplest member of the class of aromatic hydrocarbons

A

benzene

50
Q

why are benzene rings stable

A

due to the delocalisation of electrons in the conjugated system - this is why they do not take part in addition reactions

51
Q

how can bonding in benzene be explained

A

in terms of sp2 hybridisation, sigma and pi bonds, and electron delocalisation

52
Q

what is a benzene ring

A

this is when one hydrogen atom has been subsituted by a phenyl group

53
Q

what is the formula for a phenyl group

A

C6H5

53
Q

what is the formula for a phenyl group

A

C6H5

54
Q

what do reactions at benzene rings include

A
  • halogenation by reaction of a halogen using alumium chloride or iron chloride for chlorination and aluminium bromide or iron 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 (35 decks)

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