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Chemistry > Module 6-Organic Chemistry And Analysis > Flashcards

Module 6-Organic Chemistry And Analysis Flashcards

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1
Q

Evidence that disproved Kekulés model.(6)

A
  • lack of reactivity (doesn’t undergo electrophilic addition thus doesn’t decolourise Br2 like expected in kekulés model)
  • X-ray diffraction showed the length of the bonds were between that of a single bond and double bond not alternating
  • hydrogenation enthalpies-should Be expected to have 3xhydrogenation of cyclohexane but didn’t suggesting not kekulés model.
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2
Q

What 3 groups are in aromatic compounds where benzene is considered the parent chain hence is in the name?(3)

A
  • alkyl groups with less than 7 carbons, alkylbenzene
  • halogens, C6H6Cl=chlorobenzend
  • nitro groups, nitrobenzene.
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3
Q

How do you name aromatic compounds with an alkyl group containing 7 or more carbons?(1)

A

Phenyl prefix with whatever the chain is secondary.

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4
Q 
What is the IUPAC name for:
benzene carboxylic acid
Phenylamine
Benzenecarbaldehyde.
(3)
Why are they exceptions?
A

-benzoic acid
-phenylamine
-benzaldehyde.
Have strange names for only being one group on a benzene ring.

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5
Q

Reagents and conditions for nitration of benzene and products.(6)
Type of reaction?

A
  • 50 degrees, higher leads to further substitution resulting in dinitrobenzene
  • HNO3 conc
  • H2SO4 conc
  • NO2+ (nitronium ion) electrophile comes from reaction between hno3 and h2so4

H20 and nitrobenzene.
H2SO4 catalyst do reformed with H+

Electrophilic substitution.

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6
Q

Reagents, conditions and products for halogenation of benzene.(4)
Type of reaction?

A
  • halogen carrier, AlX3 (catalyst)
  • X+ eg bromonium ion B+
  • room temp and pressure

-halobenzene and HX

Electrophilic substitution.

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7
Q

Friedel-Crafts Alkylation reagents, conditions and products.(4)
Type of reaction?

A

Haloalkane
Halogen Carrier, AlX3/FeX3

  • alkylbenzene or phenyl___ depending on carbon chain length
  • HX

Electrophilic substitution.

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8
Q

Friedel-Crafts acylation reagents, conditions and products.(4)
Type of reaction?

A
  • acyl chloride
  • AlX3/FeX3 catalyst halogen carrier
  • phenyl___anone
  • HX

Electrophilic substitution.

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9
Q

What’s different between the reactivity of alkenes with arenes?(2)

A

Benzene is quite stable so relatively unreactive due to its delocalised ring structure
This electron density around any cabin is less than that in a double bond in an alkene
When a non polar molecule like bromine approaches there is insufficient pi-electron density to polarise bromine.

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10
Q

Why do benzene reactions tend to be slow?

A

High activation energy in order to temporarily disrupt the delocalised ring structure.

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11
Q

Why is phenol described as a weak acid?(1)

A

Ability to partially dissociate in water to produce the phenoxide ion (C6H5O-) and H+, like a weak acid.
Isn’t as soluble as an alcohol due to presence of non-polar benzene ring.

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12
Q

List the order of acidity of the following compounds, how would you distinguish between the 3:
Phenol
Alcohol
Carb’ acid.(3)

A

Most acid to least:
Carb acid
Phenol
Alcohol

Alcohol won’t react with strong bases eg NaOH or weak bases eg Na2CO3
Phenol reacts with strong bases such as NaOH
Only carb’ acid acidic enough to react with weak bases such as Na2CO3

React with Na2CO3 and CO2 has will be evolved if carb’ acid is present, the phenol and alcohol wouldn’t react, react with a strong base to determine which is alcohol and phenol as alcohol wouldn’t react.

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13
Q

What is the reaction between phenol and NaOH described as, what is produced?(3)

A

Neutralisation
Sodium phenoxide (C6H5O^-Na^+)
And water.

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14
Q

What two observations are there with the bromination of phenol?(2)

A

White ppt of 2,4,6-tribromophenol
Decolourises bromine water-orange to colourless

No halogen carrier required!

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15
Q

How does the nitration of phenol differ from the nitration of benzene?(3)

A

Dilute nitric acid is enough
No conc H2SO4 required
Form a mixture of 2-nitrophenol and 4-nitrophenol.

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16
Q

Why is phenol more reactive than benzene?(4)

A

Lone pair from p orbital in O in OH is fed into pi-system increasing electron density, this increase in electron density therefore makes phenol more susceptible to attack from electrophiles and is sufficient to polarise bromine without requiring a halogen carrier, hence phenol is more reactive.

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17
Q

Which out of NH2(amine) and NO2 (nitro) goes with the following:

A)2,4 directing, activates the benzene ring leading to multiple substitutions eg reaction with bromine results in 2,4,6tribromo—— with no halogen carrier required

B)3 directing, deactivates the benzene ring so to react with bromine requires both a halogen carrier and high temp to result in 3bromo——-.

A

NH2=A

NO2=B

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18
Q

Which groups are 2,4 directing?(5)what do these have in common?

A 
NH2/NHR
OH
OR
R or C6H5
F, Cl, Br, I

All activate the bezene, aside from the halogens

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19
Q

Which groups are 3 directing?(8)what do these have in common?

A 
RCOR
COOR
SO3H
CHO
COOH
CN
NO2
NR3+

All deactivate the benzene ring.

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20
Q

Methyl benzene reacts with bromine to form 2 mono-substituted organic products, what are they and which will be in higher abundance?(2)

A

2-bromomethylbenzene
4-bromomethylbenzene

Technically get “6”bromomethylbenzene but the 6 is the same position as the 2 therefore called 2 and hence twice as much 2bmb would be expected when compared to 4bmb.

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21
Q

What other factor may effect the proportions of substituted isomers?(1)

A

Steric effect-large substituted groups may get in the way thus making one isomer more likely to form.

22
Q

Why is the C=O so different to the C=C bond?(1)

A

C=O is a polar bond as oxygen is more electronegative, this means the C is susceptible to attack from nucleophiles (as opposed to electro hikes which are involved in C=C mechanisms).

23
Q

What reducing agent is usually used to reduce aldehydes and ketones?what conditions?

A

NaBH4, Sodium tetrahydridoborate (III) , warmed and in aqueous solution (aq/H2O)

One [H] required for aldehydes but 2[H] required for ketones if writing an equation.

24
Q

What reagents are used to provide HCN for the nucleophillic addition of aldehydes and ketones?why is HCN not used itself?what is useful about this reaction?what does it produce?

A

H2SO4 and NaCN, HCN is an extremely toxic liquid that boils just above room temp therefore isn’t safe in open lab, even using these reagents is still potentially very hazardous.

Provides a way of increasing carbon chain length!
A cyanohydrin/hydroxynitrile contains CtriplebondN and O-H functional groups.

25
Q

How do you test for a carbonyl compound?state the observation.(2)

A

2,4-dinitrophenylhydrazine (2,4-DNPH) aka Brady’s reagent when dissolved in methanol And h2so4 (as solid 2,4-DNPH as is a contact explosive)
Yellow/orange ppt in presence of carbonyl compound.

26
Q

What test is done to distinguish between aldehydes and ketones?describe how you would carry out such a test and state and explain any observations.(6)

A

Tollens test, ammoniacal silver nitrate has a short shelf life and should be made fresh as follows:
3cm AgNO3 (aq) + NaOH (aq)= Brown ppt of Ag2O
+ dilute NH3 until this ppt dissolves to for a clear solution (ie TOLLENS CREATED)
Using approx 2cm of both tollens and solution to be tested add to test tube and heat at 50 degrees for around 10-15 mins
Silver mirror=aldehyde
No mirror=ketone
This is because the aldehyde is oxidised to carb acid by Ag+ which is itself reduced to Ag (s) whereas a ketone cannot be oxidised hence Ag+(aq) cannot be reduced to Ag(s).

27
Q

Carb’ acids are able to form h bonds with water hence are soluble, this solubility decreases as you increase the carbon chain length as this then has a greater effect over the polarity of the molecule, when is this the case?(1)

A

When carb’ acids have 5+ carbons this is then the case, before this the carb acid is soluble in water.

28
Q

What reagents (put very simply) are used to produce an ester?what are the products?how do you name an Ester?(5)

A

Carb acid, alcohol, warmed conc’ h2So4 (catalyst), Ester and water produced.

Carb acid part used to create ending with suffix -late used eg ethanoic acid used would result in ethanoate ending
Alcohol used/alkyl group attached to O in water is the beginning of the Ester name eg if CH3 group is attached to O of the COO then it would be methyl____.
Eg is propanoic acid and ethanol mixed you would get ethyl propanoate and water.

29
Q

What are the conditions and reagents for acid hydrolysis of an Ester, what is produced?(3)

A

Essentially the opposite of esterification and so fed that reason is a reversible reaction, dilute aqueous acid catalyst used and heated under reflux producing the carb acid and alcohol that originally produced the Ester.

30
Q

What is alkaline hydrolysis of an Ester also known as, how does it differ from acid hydrolysis, what are the reagents, conditions and products?(4)

A

Saponification, is irreversible unlike acid hydrolysis and is when the Ester is heated under reflux with OH^- (aq) to produce the carb acid ion and alcohol
If NaOH is used as the alkali the sodium salt of the carb acid aspect of the Ester is formed eg is methyl ethanoate is hydrolysed using NaOH methanol and sodium ethanoate are formed.

31
Q

How do you prepare an acyl chloride from a carb acid?what is produced?(3)

A

Use SOCl2

Produce acyl chloride, SO2 and HCl which are evolved as gasses, need to use fine cupboard as these are harmful .

32
Q

How do you form an Ester using an acyl chloride?what is produced?(1)

A

Use an alcohol same as a carb acid, only difference is that Hydrogen chloride HCl is formed not H20.

33
Q

What is produced when a acyl chloride is reacted with a phenol?(2)

A

A Phenyl Ester (and HCl) unlike carb acids which are not reactive enough to do so, also don’t require H2SO4 catalyst.

34
Q

What does the reaction of an acyl chloride and water result in, what are the observations of the reaction?(3)

A

A carb’ acid, steamy HCl gas evolved also, violent reaction ensues.

35
Q

What is formed when you react ammonia with an acyl chloride, what is the equation for the reaction between ethanoyl chloride and NH3 and what does the ammonia act as?(4)

A

NH3 acts as a nucleophiles because of the the lone pair on nitrogen, Forms a PRIMARY amide

CH3COCl + 2NH3 —> CH3CONH2 + NH4Cl (ammonium chloride also produced and 2 ammonia’s required).

36
Q

What is formed when a primary amine is reacted with an acyl chloride, write the equation for the reaction between ethanoyl chloride and methyl amine.(4)

A

A SECONDARY amide

CH3COCl + 2CH3NH2 —-> CH3CONHCH3 + CH3NH3+Cl- (methylammonium chloride also produced and notice 2 methyl amines required, N-methylethanamide produced as methyl is on nitrogen).

37
Q

How do amines behave as bases?give examples.(2)

A

The nitrogen has a lone pair so has the ability to accept a proton forming a dative bond, similar to ammonia which forms the ammonium ion the same occurs with amines eg ethyl amine becomes ethylammonium ion.

They form salts in neutralisation reactions with acids similar to ammonia also eg ammonia and HCl results in ammonium chloride where as ethylamine and sulphuric acid results in ethylammonium sulphate (C2H5NH3+)2SO42-.

38
Q

How do you form a primary amine?state conditions.(4)

A

ammonia acts as nucleophiles to a haloalkane forming a haloalkane ammonium salt
Treated with an Alkali eg NaOH to form the amine and NaCl (salt if Cl and Na present) and H20

Ethanol used as solvent to prevent alcohol formation by haloalkane being substituted using water
Excess ammonia used to prevent further substitution.

39
Q

How are secondary and tertiary amines formed?(1)

A

Further substitution occurs as the NH2 on the salt which goes onto form a primary amine still has a lone pair therefore can react further with a haloalkane to form a secondary or tertiary amine in the same way as was the case for a primary amine (by forming the salt then reacting with NaOH).

40
Q

How do you produce an aromatic amine?List any conditions.(3)

A

Reduce nitrobenzene using Tin and conc’ HCl (think TinCl) forming the salt, phenylammonium ions (C6H5NH3+), H+ comes from acid and electrons come from tin(Sn)and excess NaOH to form the phenylamine and H20.
Heated under reflux!

41
Q

How do you esterify an amino acid?what happens to the amino group?(3)

A

React with an alcohol in the presence of an alcohol and H2so4 the same as with a carb acid
This results in the Ester of the AA and alcohol but with the amino group being protonated due to presence of H+ from the acid.

42
Q

What is special about an amino acid?(3)

A

It has both the basic amino group and acidic carboxyl group so reacts with both acids and bases

I’d reacted with HCl the amino group is protonated leaving the Cl-
If reacted with NaOH the sodium salt of the carboxyl group with be formed along with water (like a regular acid base reaction).

43
Q

What is a zwitterion?What is the isoelectric point?How do they react in acidic and basic conditions?(4)

A

The zwitterion is formed when the carboxyl group donates a proton to the amino group of an AA leaving a +ve charge at this end and -ve charge at the carboxyl end, they have no overall charge as the charges balance
The isoelectric point is the pH at which the zwitterion is formed

In basic conditions the NH3+ loses a proton and the AA behaves as an acid due to negative carboxyl ion
In acidic conditions the H+ reacts with the COO- and so the AA behaves as a base due to the NH3+ remaining.

44
Q

What is a chiral centre?what does it produce?(2)

A

A chiral carbon is one in which 4 diff groups are attached to the carbon,, results in optical isomers (enantiomers) which are non superimposable mirror images of one another.

45
Q

What is special about all alpha amino acids apart from glycine?(1)

A

They all have a chiral centre.

46
Q

What is condensation polymerisation?(1)

A

Th joining of monomers with the loss of a small molecule (usually water, or HCl if an acyl chloride is use instead of a carb acid)

47
Q

What is terylene?(3)

A

A condensation polymer (polyester) made from benzene-1,4-carboxylic acid and ethane-1,2-diol
It is often shortened to PET and is used in clothing, bottles and also electrical insulation.

48
Q

How can you make polyesters and polyamides(polypeptides aka protein)?(2)

A

Polyesters made from one monomer with carb acid/acyl chloride group and hydroxyl group or 2 monomers (one diol one diacyl chloride/dicarb acid)

Same for poly amides but need an amine group (NH2) rather than a hydroxyl group.

49
Q

What is nylon an example of and what monomers make it?

A

A polyamide/peptide composed of 1,6-diaminohexane and hexandioic acid.

50
Q

When making condensation polymers, how many water molecules are made for every repeat unit ‘n’?(1)

A

2n-1.

51
Q

How do you hydrolyse polyamides/peptides or polyesters?what is formed for each?(3)

A

Can be hydrolysed using a hot aqueous alkali such as NaOH or hot aqueous acid such as HCl.

Same as Ester hydrolysis for both acidic and alkaline conditions, in H+ get both constituents as before, in OH- get alcohol back and ion of dicarb acid

In the case of polyamides the dicarb is reformed in H+ however the amine groups are both protonated to NH3+.

Chemistry (6 decks)

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