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Chem > Extened Organic > Flashcards

Extened Organic Flashcards

1
Q

What is the molecular formula for benzene?

A

C6H6

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2
Q

Give three reasons why the Kekulé structure is not correct.

A

low reactivity - does not undergo electrophilic addition reactions,
carbon to carbon bond lengths all same
less exothermic enthalpy change of hydrogenation than expected

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3
Q

Describe the delocalised model of benzene

A

Planar carbon ring, 120o bond angles around carbons (trigonal planar), C-C & C-H bonds are sigma bonds, one unbonded electron per carbon in p-orbitals that overlap to create a pi bond of delocalised electrons arranged in a ring above & below the carbon ring.

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4
Q

What are the reagents and conditions for the nitration of benzene?

A

benzene + nitric acid at 50oC with sulphuric acid catalyst

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5
Q

What are the equations to show how sulphuric acid acts as a catalyst to create an electrophile?

A

HNO3 + H2SO4 -> NO2+ + HSO4- + H2O
HSO4- + H+ -> H2SO4

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6
Q

Describe the mechanism for nitration of benzene with curly arrows.

A
  1. The curly arrow starts at the delocalised system on the benzene ring and goes to the positive nitronium electrophile.
  2. A dative covalent bond has formed between the electrophile and the benzene ring. A curly arrow starts at the bond between the carbon and the hydrogen and goes to the positive intermediate.
  3. The product formed is nitrobenzene and hydrogen ion which goes on to reform the catalyst.
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7
Q

What are the reagents and conditions for the halogenation of benzene?

A

Halogen (Br2) + halogen carrier catalyst (either AlBr3 or FeBr3)

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8
Q

What are the equations to show how the halogen carrier acts as a catalyst to create an electrophile?

A

Br2 + FeBr3 -> Br+ + FeBr4-
H+ + FeBr4- -> FeBr3 + HBr

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9
Q

Describe the mechanism for halogenation of benzene with curly arrows.

A
  1. The curly arrow starts at the delocalised system on the benzene ring and goes to the positive bromonium/chloronium electrophile.
  2. A dative covalent bond has formed between the electrophile and the benzene ring. A curly arrow starts at the bond between the carbon and the hydrogen and goes to the positive intermediate.
  3. The product formed is a halobenzene and hydrogen ion which goes on to reform the catalyst.
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10
Q

How is phenol different to most alcohols?

A

Phenol is a weak acid (proton donor) and will react with strong bases e.g. sodium hydroxide (unlike most alcohols).

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11
Q

How is phenol different to carboxylic acid?

A

it doesn’t react with weak bases e.g. sodium carbonate (unlike carboxylic acids).

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12
Q

Why does phenol undergo electrophilic substitution more easily that benzene?

A

due to the lone pair on the oxygen atom of the phenol OH group becoming partially delocalised into the ring, increasing the electron density so can attract electrophiles more strongly.

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13
Q

Why does cyclohexene react more readily with bromine than benzene?

A

the higher electron density resulting from the pi-bond being localised between two carbon atoms (C=C) instead of over a ring of 6 carbons.

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14
Q

What is the reaction between phenol and bromine?

A

Phenol + Bromine -> 2,4,6 tribromophenol + Hydrogen bromide
C6H5OH + 3Br2 -> C6H2Br3OH + 3HBr

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15
Q

What are the observations of the reaction between phenol and bromine?

A

Bromine decolourises and white precipitate

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16
Q

What is the reaction between phenol and nitric acid?

A

Phenol + Nitric acid -> 2-nitrophenol or 4-nitrophenol + Water
C6H5OH + HNO3 -> C6H4NO2OH + H2O

17
Q

How does NH2 and OH direct a second substitution?

A

NH2 and OH will direct a second substitution to the 2 or 4 position.

18
Q

How does NO2 direct a second substitution?

A

NO2 will direct a second substitution to the 3 position.

19
Q

What are the oxidation reacts between an alcohol and the oxidising agent?

A

Primary alcohol + [O] -> aldehyde + H2O (distillation)
Primary alcohol + 2[O] -> carboxylic acid + H2O (reflux)
Secondary alcohol + [O] -> ketone + H2O
Tertiary alcohols do not oxidise.

20
Q

What is the reducing agent used to reduce aldehydes and ketones

A

NaBH4 to form primary and secondary alcohols respectively.

21
Q

Describe the nucleophilic addition mechanism of aldehyde/ketone with NaBH4

A
  1. The lone pair of electrons from the hydride ion is attracted and donated to the δ+ carbon atom in the aldehyde/ketone C=O bond
  2. A dative covalent bond is formed between the hydride ion and the carbon atoms of the C=O
  3. The π bond in the C=O breaks by heterolytic fission forming a negatively charged intermediate
  4. The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule.
  5. The intermediate has then been protonated to form an alcohol
22
Q

Describe the nucleophilic addition mechanism of aldehyde/ketone with NaCN/H+

A
  1. The lone pair of electrons from the cyanide ion is attracted and donated to the δ+ carbon atom in the aldehyde/ketone C=O bond
  2. A dative covalent bond is formed between the cyanide ion and the carbon atoms of the C=O
  3. The π bond in the C=O breaks by heterolytic fission forming a negatively charged intermediate
  4. The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen ion to form the product hyrdoxynitrile.
23
Q

What are the observations reacting an aldehyde, ketone or carboxylic acid with Brady’s reagent (2,4-DNPH)

A

Aldehyde + ketone = orange precipitate
Carboxylic acid = no observation

24
Q

How do you find the specific identity after reaction with Brady’s reagent?

A

purifying the orange precipitate by recrystallisation, measuring its melting point and then comparing this to known values in a database.

25
Q

What are the results of tollen’s reagent?

A

Aldehyde = silver mirror
Ketone = no observation

26
Q

Why are carboxylic acids soluble in water

A

Carboxylic acids are soluble in water as they can form hydrogen bonds.

27
Q

How are acyl chlorides made?

A

Acyl chlorides are made when the OH from a carboxylic acid is changed to a Cl (name changed from -oic acid to -oyl chloride) by reacting with SOCl2 (thionyl chloride) – SO2 & HCl gases made too.

28
Q

How are acid anhydrides made?

A

Acid anhydrides are made when two carboxylic acid molecules join together by the removal of H2O.

29
Q

What are the conditions for making an ester?

A

a conc sulphuric acid catalyst

30
Q

What are the general equations for making an ester?

A

carboxylic acid + alcohol -> ester + H2O
acid anhydride + alcohol -> ester + carboxylic acid
acyl chloride + alcohol -> ester + HCl

Chem (2 decks)

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