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Synthesis Flashcards

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1
Q

homolytic fission

A

normally occurs between pure covalent bonds, each atom will have equal share of bonding electrons, forms free radicals

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2
Q

heterolytic fission

A

normally occurs between polar covalent bonds, unequal share of bonding electrons, forms ions

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3
Q

haloalkanes

A

substituted alkanes with one or more halogen atom instead of a hydrogen atom

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4
Q

why do haloalkanes undergo nucleophilic substitution reactions?

A

presence of slight positive charge on carbon atom and polar bond with halogen makes haloalkanes susceptible to nucleophilic attack

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5
Q

monohaloalkanes undergo nucleophilic substitution reactions with:

A
  • alcoholic alkoxides to form ethers
  • aqueous alkalis to form alcohols
  • ethanloic potassium cyanide to form nitriles- end nitrile contains one more carbon than the original haloalkane
  • base induced elimination reactions to form alkenes
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6
Q

carboxylic acid preparation

A

oxidation of primary alcohols or aldehydes by heating them with acidified potassium dichromate
hydrolysis of esters, nitriles or amides by heating in the presence of acid or alkali catalyst

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7
Q

reactions of carboxylic acid

A
  • condensation reactions with alcohols to form esters (sulfuric acid catalyst)
  • reduction with lithium aluminium hydride to form primary alcohols
  • react with amino groups to form amide links
  • formation of salts by reaction with metals or bases
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8
Q

amines

A

derived from ammonia where one or more of the hyrogens are replaced with alkyl groups

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9
Q

properties of amines

A
  • hydrogen bonding in primary and secondary amines (N-H) so higher boiling points than tertiary amines
  • all amines are soluble- can form hydrogen bonds with water
  • weak bases forming alkaline solutions
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10
Q

reactions of amines

A
  • react with hydrochloric acid, sulfuric acid and nitric acid to form salts
  • react with carboxylic acids to form salts, amide are formed if these are heated losing water
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11
Q

reactions of alcohols

A
  • react with reactive alkali metals to form alkoxides
  • form alkenes in dehydration (elimination) reactions of alcohols
  • form esters by reacting with carboxylic acids or acid chlorides
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12
Q

preparation of alcohols

A

heating haloalkanes under refluc with sodium/ potassium hydroxide by nuclophilic substitution
acid catalysed hydration of alkenes
aldehydes/ ketones reacting with lithium aluminium hydride (reduction)

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13
Q

properties of alcohols

A
  • high boiling points due to hydogen bonding
  • small alcohol molecules are miscible in water but larger are insoluble (as non polar end of molecules increases, solubility decreases)
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14
Q

properties of ethers

A
  • lower B.Ps than alcohols because they don’t have hydrogen bonding
  • can form hydrogen bonds with water so small molecules are solutble
  • flammable and when exposed to air form peroxides can be explosive
  • can be used as solvents- chemically inert, volatile
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15
Q

preparation of ethers

A

formed when monohaloalkanes react with alcoholic alkoxides

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16
Q

preparation of alkenes

A
  • dehyration of alcohols using aluminium oxide, concentrated sulfuric acid or phosphoric acid
  • base induced elimination of hydrogen halides from monohaloalkanes
17
Q

markinokov’s rule

A

hydrogen is mainly added to the carbon in the alkene that is already bonded to the most hydrogens in an addition reaction of alkenes

18
Q

alkenes undergo electrophilic reactions in

A
  • halogenation (addition of halogens)

- hydrohalogenation- H already has a slighly positive charge

19
Q

why do alkenes undergo electrophilic reactions?

A

there is high electron density at C=C which attracts electrophiles

20
Q

SN1 reactions

A

substution reactions involving a nucleophile in which 1 species is involved in the rate determining step
involves heterolytic fission forming two ions, one being a carbocation
carbocations formed are intermediate
has 2 steps, first being RDS

21
Q

SN2 reactions

A

substution reactions involving a nucleophile in which 2 species are involved in the rate determining step
has 1 step
two species involved form an unstable trasition state

22
Q

inductive effect

A

alkyl groups are electron donating and push electrons to the positively charged carbocation carbon which increases stability, means tertiary haloalkane is more likely to SN1

23
Q

steric effect

A

alkyl groups are bulkier than H atoms so it is more difficult for nucleophile to attach and form partial bond on central carbon- tertiary haloalkanes are less likely to SN2

24
Q

simplest aromatic compound

A

benzene

25
Q

molecular formula of benzene

A

C6H6

26
Q

how do you know benzene does not have double bonds?

A

does not readily decolourise bromine water

27
Q

shape of benzene

A

linear hexagonal

28
Q

benzene molecular orbitals

A
  • sp2 hybridised
  • three filled sp2 hybrid orbitals form sigma bonds with 2 neighbouring C atoms and a H atom
  • leaves an elctron occupying a p orbital on each carbon atom, each of these orbitals overlap side on with two p orbitals on each side which forms a pi molecular orbital
  • six electrons in the pi orbital are delocalised and shared by all 6 carbon atoms
29
Q

why does benzene undergo substitution reactions rather than addition reactions?

A

delocalised electrons give benzene unusual stability so addition reactions would disrupt the stability of the ring

30
Q

what type of reactions does benzene undergo?

A

delocalised electrons attract electrophiles which can substitute/ replace H atom(s)= electrophillic subtituion reactions

31
Q

electrophilic substitution reaction mechanism with benzene

A
  • electrophile attacks one of the carbon atoms in the ring
  • forms an intermediate with a postive charge that can be stabillised by delocalisation around the ring
  • the intermediate ion then loses the H+ ion to regain aromatic character and restore the system
32
Q

examples of electrophilic substitution reactions in benzne and other aromatic compunds

A

alkylation, nitration, sulfonation, halogenation

33
Q

when one of the hydrogen groups has been substituted in a benzene ring it is known as

A

a phenyl group (C6H5)

Advanced Higher Chemistry (8 decks)

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