Ocr Chemistry Module 6

Front 1

What are carbonyls?

Back 1

A structure containing a carbon-oxygen double bond

Front 2

What is special about the bond in carbonyls and why?

Back 2

It is polar due to the difference in electro negativities of the Carbon and Oxygen.

Front 3

How to make an aldehyde from an alcohol

Back 3

Heat a PRIMARY alcohol with acidified (with sulphuric acid (aq)) K2Cr2O7 (potassium dichromate) under distillation so it doesn't continue to be oxidised to a carboxylic acid.

The orange Cr2O7- is reduced to green Cr3+

Front 4

Show the oxidation reaction of ethanol to ethanoic acid

Back 4

CH3CH2OH (l) +[O] -> CH3CHO (l) + H2O (l)

Front 5

Show the oxidation reaction of the secondary alcohol propan-2-ol

Back 5

CH3CHOHCH3 (l) + [O] -> CH3COCH3 (l) +H2O (l)

Heated under reflux with acidified potassium dichromate

Front 6

Which is easier to oxidise out of aldehydes and ketones?

Back 6

Aldehydes

Front 7

How do you oxidise ketones?

Back 7

Use a powerful oxidising agent under vigorous conditions to carboxylic acids but with fewer carbons

Front 8

What happens if aldehydes and ketones are heated with a mild oxidising agent?

Back 8

Aldehyde -> carboxylic acid

Ketone -> no change

Front 9

How to identify a carbonyl compound

Back 9

Formation of orange crystalline precipitate with 2,4-dinitrophenylhydrazine (2,4-DNPH)

Strong peak at 1400-1600 cm-1 in the infrared spectrum

Front 10

How to determine if ketone or aldehyde after 2,4-DNPH?

Back 10

Use Tollen's Reagent, it acts as a mild oxidising agent and will oxidise aldehydes but not ketones.

The silver(I) ion is reduced to silver: Ag+(aq) +e- -> Ag (s)

Positive result for an aldehyde will form a SILVER MIRROR

Front 11

What type of mechanism occurs with both carbonyls?

Back 11

Nucleophilic addition - addition to the polar C=O bond, attack is by nucleophiles at the positive carbon centre.

Front 12

State the reagent, conditions, mechanism and nucleophile for the reduction of carbonyls

Back 12

Reagent: Sodium Tetrahydridoborate (III) NaBH4

Conditions: aqueous or alcoholic solution

Mechanism: Nucleophilic addition

Nucleophile: H- (Hydride Ion)

Front 13

What are aldehydes and ketones REDUCED to?

Back 13

Aldehydes: Primary Alcohols

Ketones: Secondary Alcohols

Front 14

Show reduction equation of ethanal

Back 14

CH3CHO + 2[H] -> CH3CH2OH (NO WATER)

Front 15

Show the reduction equation of propan-2-one

Back 15

CH3COCH3 + 2[H] -> CH3CHOHCH3

Front 16

Draw the mechanism for nucleophilic addition of ethanal

Front 17

State the conditions, nucleophile and product when a carbonyl is reduced by potassium cyanide

Back 17

Heat under reflux

Nucleophile: Cyanide ion CN-

Product: Hydroxynitrile

Front 19

Explain what Kekule's model of benzene was

Back 19

He suggested a PLANAR, CYCLIC structure with ALTERNATING DOUBLE AND SINGLE BONDS.

With three localised double bonds

Front 20

What was wrong with Kekule's model? (3 problems)

Back 20

Benzene doesn't readily undergo electrophilic addition so doesn't have proper C=C bonds.

All bond lengths were similar, when really double bonds are shorter than single ones.

The ring was thermodynamically more stable than expected.

Front 21

Explain the now accepted theory of the structure of Benzene.

Back 21

The six pi electrons making up the double bonds are delocalised around the ring due to sideways overlapping of the p orbitals.

Still gave a PLANAR structure.

More stable, didn't undergo electrophilic addition

Front 22

State the reagents, conditions, type of mechanism and product of nitration of benzene?

Back 22

Reagent: Concentrated Nitric acid

Conditions: Catalyst-conc sulphuric acid, reflux at 55 Celsius

Mechanism: ELECTROPHILIC SUBSTITUTION

Product: Nitrobenzene

Front 23

Show the equation for mononitration of benzene

Back 23

C6H6 + HNO3 -> C6H5NO2 +H2O

Front 24

Draw and explain the mechanism for the nitration of benzene

Back 24

(Google mechanism)

An electron pair leaves the delocalised system to form a bond to the electrophile

This disrupts the stable delocalised system and forms an unstable carbon cation intermediate

To restore stability, the pair of electrons in the CH bond moves back to the ring

Overall there is a substitution of hydrogen

The electrophile is (NO2)+

Front 25

Show how the electrophile for the nitrification of benzene is formed

Back 25

2H2SO4 + HNO3 (reversible arrow) (2HSO4)- + (H3O)+ + (NO2)+

Front 26

Why does the temperature need to be controlled in the nitrification of benzene?

Back 26

The higher temp means there is more chance for more nitronium ions to be substituted on to the benzene.

Front 27

State the reagents and conditions for the halogenation of benzene

Back 27

Reagents: Chlorine

Conditions: Reflux in the presence of a halogen carrier such as Aluminium Chloride

Front 28

State the overall equation for the halogenation of benzene

Back 28

C6H6 +Cl2 -> C6H5Cl +HCl

Front 29

What is the role of the halogen carrier in halogenation of benzene?

Back 29

Chlorine is non polar so not a good electrophile. The halogen carrier polarises the halogen.

Front 30

Show the formation of the electrophile for halogenation of benzene

Back 30

Cl2 + AlCl3 (reversible arrow) (AlCl4)- + Cl+

Anhydrous aluminium chloride is the catalyst

Front 31

Show the reformation of the halogen carrier

Back 31

H+ + (AlCL4)- -> AlCl3 +HCL

Front 32

Compare the electrophilic addition of benzene with alkenes

Back 32

The conditions are much tougher than with alkenes because the delocalised system makes benzene more stable and less reactive