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Carbonyls Flashcards

1
Q

what is the structure of the carbonyls?

A

carbonyl compounds contain the carbonyl functional groups (c=o)

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2
Q

what are the carbonyl compounds sub-divided into?

A
  • aldehydes
  • ketones
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3
Q

what is the structure of aldehydes?

A

contain the carbonyl functional group attached at the end of the chain of carbon atoms and have one or more hydrogen atoms directly attached to the carbonyl functional group.

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4
Q

how do you name the aldehyde?

A

To name an aldehyde use the name of the alkane but change the end -e to –al.
When naming aldehydes, the carbon bonded to the oxygen is carbon number 1.

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5
Q

what is the structural formula of ketones?

A

Ketones contain the carbonyl functional group in the middle of the carbon chain, (between two carbon atoms), so do not have a hydrogen atom attached directly to the functional group.

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6
Q

how do you name a ketone?

A

use the name of the alkane but change the end -e to -one

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7
Q

what carbonyl function group is it, and what is the angle?

A

The carbonyl functional group is a planar group, with a bond angle of approximately 120°.

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8
Q

what is the double bond of the carbonyl made of?

A

The double bond is made up of a single sigma (σ) bond (end-on overlap of atomic orbitals)
and a pi (π) bond (side-on overlap of p-orbitals), in exactly the same way as an alkene double bond.

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9
Q

in the carbonyl group, the oxygen atom…

A

is much more electronegative than carbon. which causes the carbonyl group to be polar

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10
Q

what is the oxygen and carbon atom polar represented by?

A

the idol

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11
Q

what bond of the carbonyl functional group and angle?

A

Trigonal Planar with a bond angle of 120 degrees

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12
Q

what is different between esters and carboxylic acids?

A

Esters & carboxylic acids contain the carbonyl group but are not carbonyl compounds

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13
Q

what are the only carbonyl compounds?

A

The ONLY carbonyl compounds are aldehydes & ketones

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14
Q

what are aldehydes formed from?

A

1o alcohols

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15
Q

what is the Reagent to form aldehydes?

A

potassium dichromate and conc sulfuric acid

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16
Q

what is the conditions to form aldehydes?

A

Distillation

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17
Q

what colour shows the the formation of aldehydes?

A

Dichromate goes from orange to green

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18
Q

what are ketones formed from?

A

2o alcohols

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19
Q

what Reagant forms ketones?

A

potassium dichromate and conc sulfuric acid

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20
Q

what conditions forms ketones?

A

Reflux

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21
Q

what colour shows the formation of ketones?

A

Dichromate goes from orange to green

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22
Q

what is the equation to show formation of aldehydes?

A

RCH2OH + [O] –> RCHO + H2O

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23
Q

what is the equation to show formation of Ketones?

A

RCHOHR’ + [O] –> RCOR’ + H2O

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24
Q

what is the identification/test for carbonyl compounds?

A

2,4-dinitrophenylhydrazine (2,4-DNPH) solution can be used to identify the presence of a carbonyl functional group.

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25
what is the positive test result for carbonyl compounds?
The positive test for a carbonyl is the formation of an orange/red precipitate when a few drops of the carbonyl compound is added to the 2,4-DNPH solution.
26
what can you use to identify an actual carbonyl?
We can use the product of the reaction with 2,4,DNPH (the orange crystals) along with a data base to identify the actual carbonyl.
27
what is the method for identifyind a specific carbonyl compound by melting point?
1. Add 2.4-DNPH 2. Purify the orange crystals formed by recrystallisation 3. Measure the melting point of the purified crystals 4. Compare the melting point to a data base of melting points
28
what is the key difference between an aldehyde and a ketone?
The key difference between an aldehyde and a ketone is the presence of a hydrogen atom attached to the carbon-oxygen double bond in the aldehyde.
29
if ketones don't have a hydrogen, what does this mean?
it can't be easily oxidised
30
what does the presence of hydrogen atoms mean?
The presence of that hydrogen atom makes aldehydes very easy to oxidise.
31
what are very strong oxidising agents that oxidise ketones ?
acidified potassium manganate(VII) solution (potassium permanganate solution)
32
how are the ketones oxidised?
they do it in a destructive way, breaking carbon-carbon bonds.
33
colour shown by these compounds: MnO4-(aq) → MnO2(s) / Mn2+(aq)
purple → brown ppt / colourless solution
34
what do you observe in the oxidation of aldehydes to carboxylic acid with acidified potassium dichromate conc H2SO4/K2Cr2O7 ?
Orange to green solution
35
what is the equation for the acidified potassium dichromate conc H2SO4/K2Cr2O7?
Cr2O72- → 2Cr3+ Orange green RCHO + [O] → RCOOH
36
what do you observe in the oxidation of aldehydes to carboxylic acid with Tollens' Reagent/[Ag(NH3)2]+. / ammoniacal silver nitrate solution?
Colourless solution to a grey precipitate (ppt) of silver/a silver mirror.
37
what is the equation for the Tollens' Reagent/ [Ag(NH3)2]+. / ammoniacal silver nitrate solution?
Ag+(aq) → Ag(s) RCHO + [O] → RCOOH
38
what are the observations in the oxidation of aldehydes to carboxylic acid with Fehling's / Benedict's solution Cu2+(aq) in an alkaline solution ?
The blue solution to a dark red ppt of Cu2O(s)
39
what is the equation for the Fehling's / Benedict's solution Cu2+(aq) in an alkaline solution?
Cu2+(aq) → (Cu+)(s) as Cu2O RCHO + [O] → RCOOH
40
if you add 2,4-DNPH, and there is no reaction what does this mean?
NOT a ketone or an aldehyde
41
if you add 2,4-DNPH, and there is orange crystals/solid what does this mean?
Carbonyl compound (aldehyde or ketone)
42
if you add tollens or fehlings and there is no reaction, what does this mean?
its a ketone
43
if you add tollens or fehlings and there is a Silver mirror / brick red ppt, what does this mean?
aldehyde
44
what do aldehydes reduce to?
primary alcohols
45
what do ketones reduce to?
secondary alcohols
46
what is the reagant used for reduction of carbonyl compounds?
NaBH4(aq)
47
what is the conditions used for reduction of carbonyl compounds?
aqueous solution & warm
48
what is the equations used for reduction of carbonyl compounds?
49
what will R be for an aldehyde?
For an aldehyde, either R’ or R” will be a hydrogen atom. r can be a hydrogen or a carbon / alkyl group.
50
what will the R be for a ketone?
For a ketone, both will be carbon / alkyl groups.
51
what is the mechanism for the reaction?
nucleophilic addition
52
what is the nucleophile for he reaction?
:H- A hydride ion
53
what is the mechanism of nucleophilic addition?
Draw the dipole on the C=O Draw a curly arrow from the lone pair on the hydride ion to the Cδ+ Draw a curly arrow from the C=O bond to the O to indicate the π-bond breaks Draw the intermediate formed with a –ve charge on the oxygen. Draw a water molecule with dipoles Draw a curly arrow from the lone pair on the oxygen to the Hδ+ of the water molecule. Draw a curly arrow to show the H-O bond breaking in the water molecule
54
Reaction of carbonyls with hydrogen cyanide H-CΞN mechanism
nucleophilic addition reaction
55
What is the reagents used do the reaction of carbonyls with hydrogen cyanide H-CΞN?
Sodium cyanide, NaCN. and Concentrated sulfuric acid, H2SO4
56
what is the equation for the formation of HCN?
NaCN + H2SO4 → HCN + NaHSO4
57
is HCN a weak or strong acid, show the equation?
HCN is a weak acid HCN ⇌ H+ + CN-
58
Q. Why do you think it is made in situ?
Hydrogen cyanide is an extremely poisonous volatile liquid. (Bpt: 26oC). Making it in situ improves safety (although still extremely hazardous) and increases reaction rat
59
what is the general equation for the reaction of carbonyls with hydrogen cyanide H-CΞN?
60
what are the two functional groups the product contains?
OH group and nitrile (C=N)
61
what is the product formed in the reaction of carbonyls with hydrogen cyanide H-CΞN?
hydroxynitrile
62
State the mechanism for the reaction of hydrogen cyanide with propanal. Name the product and identify the nucleophile.
Mechanism: nucleophilic addition. Nucleophile: CN cyanide ion
63
describe the mechanism for the reaction of hydrogen cyanide with propanal.
This is nearly identical to the mechanism with the hydride ion, :H-. Just substitute the :CN- for the :H-. In the final step where hydrogen is added to the O-, this can come from a H+ in this mechanism, or water like the previous one.
64
what is optical isomerism?
Molecules with the same structural formula but different spatial arrangement of atoms.
65
optical isomerism is a type of...
stereoisomerism
66
what are the two types of stereoisomerism?
- Geometric isomerism (found in alkenes cis/trans, E/Z) - Optical isomerism
66
what is each optical isomer called?
enantiomer
67
what are the key features of optical isomers?
- Contain a chiral carbon i.e. a carbon with 4 different groups attached.  - They form non-superimposable mirror images.
68
how can optical isomers be distinguished from each other?
Each isomer/ enantiomer will rotate plane polarised light in opposite directions
69
what is the polarimeter?
used to measure the optical rotation of molecules in solution
70
what does the polarimeter tube contain?
an optical active substance in a solution which causes the plane of a polarised light to rotate
71
what is an analyser in a polarimeter?
a rotatable polariser. This lens is rotated until no light goes through the second lens. The angle is then measured to determine the optical rotation of the Amino Acid solution
72
what are examples of optical isomers in nature?
Most amino acids have chiral carbons and hence show optical isomerism. However, LIVING systems only have ONE of the enantiomers present (the L isomer in the case of amino acids and D isomers in the case of glucose)
73
what happens when optically active molecules are synthesised?
However when optically active molecules are SYNTHESISED in the laboratory both enantiomers are produced.
74
when both enantiomers are produced, what is this called?
racemic mixture or racemate and will be a 50:50 (equip-molar) mixture of both enantiomers.
75
why are racemic mixtures optically inactive?
as each enantiomer will rotate the plain polarised light in opposite directions which will cancel each other out.
76
How do optical isomers form during chemical reactions?
- a planar carbonyl molecule like ethanal.
77
what will forming a planar carbonyl molecule cause?
This will result in both possible enantiomers being produced in equal quantities as attack from above and below is equally likely.
78
2. The pi-bond in carbonyl compounds reacts readily with nucleophiles, but not with electrophiles. Describe the pi-bond in a carbonyl group and explain why this pi-bond does not react readily with electrophiles
pi bond forms when 2 p-orbitals overlap side on over C and O this bond lies above and below the C-O sigma bond
79
 Explain why carbonyl compounds react with nucleophiles and illustrate your answer by showing the mechanism for the reaction of methanal with a suitable nucleophile.
The C=O bond has a dipole with the C d+ and the O d- electrophiles are repelled by C d+ or nucleophiles are attracted to C d+

chemistry sem 2 (10 decks)

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