Chapter 26 - Carbonyls

Question 1

How to remember than an aldehyde has a C=O at the end of the carbon chain?

Answer 1

aldehyDe enD

Question 2

Why is a colour change from orange to green observed?

Answer 2

change in oxidation state of the chromium gives the colour change

Question 3

the importance of adding CN to a carbonyl compound?

Answer 3

• inc no. of Cs in a molecule

- hydroxynitriles (product formed) are used in industrial processes

Question 4

all carbonyl compounds contain a ?

Answer 4

C=O

Question 5

Why do we use Brady’s reagent and recrystallise (ect) instead of just measuring the BP of the aldehyde/ ketone ?

Answer 5

BPs can be very similar, melting points of the precipitates have a much larger diff so easier to distinguish using this

Question 6

the proper name for Tollens’ reagent is?

Answer 6

ammonical silver nitrate

Question 7

How do we make Tollens reagent?

Answer 7

• add silver nitrate solution to a test tube
• add a few drops of NaOH, a pale brown precipitate forms
• add dilute ammonia drop-wise until the precipitate dissolves

Question 8

after making Tollen’s reagent?

Answer 8

• add ketone/ aldehyde to the test tube
• place the test tube in a water bath
• DON’T USE A BUNSEN AS ALDEHYDES AND KETONES ARE FLAMMABLE

Question 9

how to get rid of anti-bumping granules?

Answer 9

hot filtration

Question 10

how are liquids always seperated?

Answer 10

distillation

Question 11

how to determine purity of a substance?

Answer 11

• IR
• MS
• Measure BP, compare to data book
• pure substances melt over a narrow range of temps

Question 12

aldehyde vs ketone?

Answer 12

H attached to C=O makes it an aldehyde

Ketones hv carbonyl bond in middle (made from secondary acl)

Question 13

ketone ending?

Answer 13

-one

Question 14

aldehyde ending?

Answer 14

-al

Question 15

what happens when propanal is added to water?

Answer 15

• no mixing

- extra CH2 means molecule has greater SA so more induced dipole forces

Question 16

what happens when propanone is added to water?

Answer 16

mixes

• dipole means H bonds can form w water
• less induced dipole forces than in propanal so easier to overcome

Question 17

what happens when propanal is added to Na2Cr2O7 ?

Answer 17

• Oxidation: propanal + [O] ➡ propanoic acid
• orange ➡ green colour change
• Reduction: 14H+ + Cr2O7 2- + 6e- ➡ 2Cr3+ (green)+ 7H2O

Question 18

what happens when propanone is added to Na2Cr2O7?

Answer 18

stays orange no oxidation occurs

Question 19

what is Tollen’s reagent?

Answer 19

Oxidising agent

Question 20

What happens when propanal is added to Tollens?

Answer 20

• Ox: propanal + [O] ➡ propanoic acid

- Red: Ag++ e- ➡ Ag (silver mirror)

Question 21

what happens when propanone is added to tollens

Answer 21

• clear: precipitate dissolves in ammonia

- doesn’t oxidise; no silver mirror

Question 22

what is Brady’s reagent also known as?

Answer 22

2,4-DNP

Question 23

What does brady’s reagent do?

Answer 23

detects C=O

+ result is orange crystals

Question 24

how to work out which aldehyde/ ketone from Brady’s + result?

Answer 24

• distil orange crystals
• measure BP
• compare to values in databook to identify

Question 25

nucleophile definition?

Answer 25

a species w a lone pair of electrons that can be donated to form a dative covalent bond

Question 26

in organic chemistry?

Answer 26

• Ox: addition of O2

- Reduction: addition of H

Question 27

reduction of carbonyl compounds is?

Answer 27

• the opposite of oxidation

- primary/ secondary alcohols are produced

Question 28

for carbonyl compounds to be reduced there must be ?

Answer 28

• powerful reducing agent - NaBH4 (aq)

- HAS TO BE IN WATER

Question 29

Ketone to 2° alcohol equation?

Answer 29

ketone + 2[H] ➡ 2° alcohol

Question 30

aldehyde to 1° alcohol equation?

Answer 30

aldehyde + 2[H] ➡ 1° alcohol

Question 31

reduction of carbonyl compounds is?

Answer 31

nucleophilic addition (double bond remember)

Question 32

reduction of CCs NA mechanism number of steps and arrows?

Answer 32

3 steps, 4 curly arrows (check for arrow on C=O)

Question 33

Where do the hydride ions come from for the reduction of CCs?

Answer 33

BH4-

Question 34

reaction of CCs w HCN?

Answer 34

• NOT A REDUCTION - CN & H added not just H

- either KCN/ HCN and H2SO4 are the reagents

Question 35

what is the problem w HCN?

Answer 35

• toxic
• low BP - vaporises- dangerous
• so we make it

Question 36

why do we react CCS w HCN?

Answer 36

It can be used to ⬆ the no. of Cs in an organic molecule which is useful for organic synthesis

Question 37

what is produced by the reaction of CCs w HCN?

Answer 37

hydroxynitriles

Question 38

hydrogen cyanide creation?

Answer 38

• happens in situ
• H2SO4 + NaCN ➡NaHSO4 + HCN (weak acid)

HCN reversible ➡H+ CN- nucleophile (has lone pair on C)

Question 39

⭐ be careful when naming hydroxynitriles?

Answer 39

the C of the CN becomes C1

Question 40

HCN + CC ➡ hydroxynitrile: number of steps/ arrows in mechanism?

Answer 40

• 3 curly arrows

- 2 steps

Question 41

when writing mechanism of HCN + CC ⭐

Answer 41

remember to start w formation/ dissociation of HCN

Question 42

the carbonyl bond is made up of?

Answer 42

1 sigma, 1 Pi bond

p orbitals overlap sideways to form the Pi bond