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Chemistry > Yr 2 Organic chem > Flashcards

Yr 2 Organic chem Flashcards

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1
Q

What is the molecular formula for benzene?

A

C6H6

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2
Q

What is the experimental evidence for the delocalised structure of benzene?

A

Bond lengths - All the same, when C=C bonds are shorter than C-C bonds. all somewhere between the bond length of a single and double carbon-carbon bond
Enthalpy change of hydrogenation - for Cyclohexene is -120kJ per mole, in Cyclohexadiene it is -240kJ per mole, meaning for the Kekule structure the expected enthalpy change would be -360kJ per mole, but it is actually much less exothermic (-208kJ per mole) - actual structure of benzene is more stable than the Kekulé structure
Resistance to reaction - if contained C=C bonds would decolourise bromine water, but it does not - more resistant to reaction than alkenes, does not react by electrophilic addition

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3
Q

What is a substituent group?

A

An atom or group of atoms that takes the place of another.

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4
Q

What are benzene and substituted aromatic hydrocarbons called?

A

Arenes

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5
Q

What conditions are required for the nitration of benzene and what is the reaction mechanism?

A

50C, conc sulfuric acid catalyst and conc nitric acid

Electrophilic substitution

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6
Q

What is used as a catalyst for the halogenation of benzene?

A

A halogen carrier, e.g. AlBr3

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7
Q

When an acyl chloride reacts with benzene by electrophilic substitution what is formed?

A

An aromatic ketone

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8
Q

Explain how phenols are weak acids

A

They partially dissociate in water to form phenoxide ions and protons. They are more acidic than alcohols but less acidic than carboxylic acids

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9
Q

How can you distinguish between a carboxylic acid and a phenol?

A

Add sodium carbonate - carboxylic acids react to form carbon dioxide gas, phenols do not react and no effervescence occurs

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10
Q

What type of reaction is the reaction of phenol with sodium hydroxide?

A

Neutralisation

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11
Q

What is used to reduce carbonyls?

A

NaBH4 (H- hydride ion)

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12
Q

What are used to produce HCN?

A

NaCN and H2SO4

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13
Q

What is used to detect the presence of the carbonyl group and what is observed?

A

2,4-DNPH, orange precipitate forms

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14
Q

How can the 2,4-DNPH derivative be analysed to identify the carbonyl compound?

A

Impure orange solid is filtered then recrystallised to produce a pure sample of the 2,4-DNPH derivative. The melting point of the purified 2,4-DNPH derivative is determined. The melting point is matched to a database of melting points for 2,4-DNPH derivatives of carbonyl compounds

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15
Q

What is used to determine the presence of an aldehyde? What is observed?

A

Ammoniacal silver nitrate (Tollens’ reagent)

Silver mirror on inside of boiling tube

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16
Q

Why do ketones not form a silver mirror when reacted with tollens’ reagent?

A

They cannot be reduced any further (by Ag+ ions in this case), whereas aldehydes can (to carboxylic acids)

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17
Q

What are the reagents and conditions for esterification?

A

Concentrated sulfuric acid, warm

18
Q

Acid hydrolysis of esters

A

Reflux with dilute sulfuric acid - reverse reaction to esterification

19
Q

Alkaline hydrolysis of esters

A

Reflux with aqueous alkali - forms carboxylate ion and alcohol - irreversible

20
Q

How are acyl chlorides prepared?

A

By reacting carboxylic acids with thionyl chloride (SOCl2)

21
Q

What can acyl chlorides be used to produce?

A

Esters (aliphatic and aromatic), carboxylic acids, primary and secondary amides

22
Q

How do you produce a carboxylic acid from and amide?

A

React it with water (HCl is second product)

23
Q

How do you form a primary amide from an acyl chloride?

A

React with ammonia

CH3COCl + 2NH3 –> CH3CONH2 + NH4+Cl-

24
Q

How do you form a secondary amide from an acyl chloride?

A

React with an amine

CH3COCl + 2CH3NH2 –> CH3CONHCH3 + CH3NH3+Cl-

25
Q

Why would an acid anhydride be used over an acyl chloride?

A

Less reactive so are useful for laboratory reactions where acyl chlorides may be too reactive

26
Q

Give an example of a tertiary amine

A

Trimethyl amine

27
Q

How do amines act as bases?

A

The lone pair on the N atom can accept protons (H+ ions) in aqueous solution to form dative covalent bonds (___ammonium ions)

28
Q

Show the reaction of ethylamine with hydrochloric acid. What type of reaction is this?

A

CH3CH2NH2 + HCl –> CH3CH2NH3+Cl-

Neutralisation reaction

29
Q

How are primary amines prepared?

A

CH3CH2Cl + NH3 –> CH3CH2NH3+Cl-
CH3CH2NH3+Cl- + NaOH –> CH3CH2NH2 + NaCl + H2O
Ethanol is used as a solvent to prevent substitution of haloalkane by water to produce alcohols - excess ammonia in ethanol

30
Q

How are aromatic amines produced?

A

C6H5NO2 + 6[H] –> C6H5NH2 + 2H2O
1 Sn/conc HCl (reducing agent)
2 excess NaOH(aq)

31
Q

What do you need to remember when amino acids are esterified?

A

The NH2 amine group is protonated, so a proton must be involved in the reactants of the equation

32
Q

Where are optical isomers found in organic chemistry?

A

In molecules that contain a carbon atom that is a chiral centre you fucking moron bitch.
A chiral carbon atom is bonded to four different atoms or groups of atoms

33
Q

What are optical isomers?

A

Non-superimposable mirror images with a chiral centre

34
Q

What does acid hydrolysis of polyamides produce?

A

Dicarboxylic acid and diammonium salt

35
Q

What does alkaline hydrolysis of polyamides produce?

A

Dicarboxylate salt and diamine

36
Q

How do you calculate number of optical isomers?

A

2 to the power of n (n being the number of chiral carbon atoms)

37
Q

What is the reaction mechanism for the conversion of haloalkanes into nitriles and what is required?

A

Nucleophilic substitution

Ethanol is required as a solvent

38
Q

How are nitriles reduced (to amines) and what is the catalyst?

A

By reacting them with hydrogen in the presence of a nickel catalyst

39
Q

How are nitriles hydrolysed to carboxylic acids?

A

Heating with dilute aqueous acid (HCl)

40
Q

Minimum volume of hot solvent added (recrystallisation)

A

Yes.

Chemistry (7 decks)

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