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Chemistry > Carbonyls > Flashcards

Carbonyls Flashcards

1
Q

What is a carbonyl bond?

A

C=O

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2
Q

Describe a carbonyl bond.

A

Carbonyl bonds form sigma and pi bonds in the same way that C=C bonds do, with the overlap of p orbitals. They are polar due to the electronegativity of oxygen.

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3
Q

WHat is the shape around a C atom in a carbonyl bond?

A

Trigonal planar with a 120 degree bond angle.

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4
Q

What is the functional group of an aldehyde?

A

-CHO

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5
Q

What is the functional group of a ketone?

A

-CO-

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6
Q

What is the functional group of an ester?

A

-COO-

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7
Q

What is an acyl chloride?

A

A carboxylic acid with a chlorine atom instead of an OH group

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8
Q

What is the functional group of an acyl chloride?

A

-COCl

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9
Q

What is Brady’s reagent?

A

2, 4- DNPH dissolved in phosphoric acid and methanol

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10
Q

Describe the appearance of Brady’s reagent.

A

A clear orange solution.

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11
Q

How does Brady’s reagent react with carbonyls?

A

Carbonyl compounds form an orange precipitate (a 2,4-DNPH derivative) in Brady’s reagent.

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12
Q

What is the test for a carbonyl compound?

A

Brady’s reagent.

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13
Q

How can 2,4-DNPH derivatives be used to identify carbonyls?

A

They have varying melting points.

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14
Q

What is the test for aldehydes?

A

Tollens’ reagent.

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15
Q

What is tollens’ reagent?

A

Ammoniacal silver nitrate.

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16
Q

How does tollens’ reagent react with aldehydes?

A

It oxidises them to carboxylic acids, and the reduced silver deposits on the test tube in a silver mirror.

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17
Q

Why does tollens’ reagent not react with alcohols?

A

It is not a sufficiently strong oxidising agent.

18
Q

What is NaBH4?

A

A reducing agent

19
Q

How does NaBH4 act as a reducing agent for carbonyls?

A

It releases hydride ions (H-) which attack the delta+ charge in the carbonyl bond.

20
Q

Name the mechanism for the reduction of carbonyls.

A

Nucleophilic addition.

21
Q

Describe the mechanism of the reduction of a carbonyl.

A

A hydride ion donates an electron pair and bonds to the C delta+ of a carbonyl bond and the C=O bond splits heterolytically leaving a single bonded O- ion. The O- ion donates an electron to bond with an H delta+ from water, and an OH- ion from that water molecule is left over.

22
Q

How does reduction affect a carbonyl bond?

A

It changes from C=O to C-OH

23
Q

Why can reduction not occur in acidic solution?

A

The hydride ion would react with an H+ ion to give hydrogen, rather that reducing the carbonyl.
H- + H+ —–> H2

24
Q

What is a cyanide ion?

A

CN-

A carbon and nitrogen atom, triple bonded, where the C atom’s lone pair contains a borrowed electron

25
Q

What is hydrogen cyanide?

A

H+ with CN-

26
Q

Which atom in a cyanide ion acts as a better nucleophile?

A

The carbon atom as it is less electronegative than nitrogen.

27
Q

Describe the reaction mechanism between a carbonyl and a cyanide ion.

A

The C atom from cyanide donates a lone pair to the C delta+ in the carbonyl bond to form a new covalent bond. The pi bond from the C=O group spilts heterolytically, leaving a singly bonded O- group. The O- group donates an electron pair to an H+ ion to form a new -OH group.

28
Q

What is the product of the reaction between CN- and a carbonyl.

A

A hydroxy nitrile with an extended carbon chain.

29
Q

Why is the addition reaction of CN- and C=O important in synthesis?

A

It allows chemists to extend the carbon chain of molecules.

30
Q

What type of molecule is hydrogen cyanide?

A

A weak acid.

HCN H+ + CN-

31
Q

How does [H+] affect the abundance of CN- in a reaction.

A

It reduces the concentration of CN- as it causes the equilibrium of the weak acid to shift towards HCN, removing H+ and CN- from the solution.

32
Q

How does [H+] affect the rate of reaction Between -O- ions and H+.

A

A higher concentration of H+ ions increases reaction rate

33
Q

Under what conditions does the addition of CN- with C=O usually take place?

A

CN- salt is used (eg. KCN) and a small amount of acid is added.

34
Q

What is acid hydrolysis?

A

The process of converting a nitrile group to a carboxylic acid.

35
Q

What are the conditions for acid hydrolysis?

A

Hot aqueous HCl.

36
Q

Give a general equation for acid hydrolysis.

A

Nitrile + 2H2O + HCl —–> Carboxylic acid + NH4Cl

37
Q

Give a general equation for the reduction of nitriles.

A

Nitrile + 4[H] —–> Amine

38
Q

What is an amine group?

A

NH2

39
Q

What are the conditions for the reduction of nitriles?

A

Hydrogen and a nickel catalyst.

40
Q

WHat is the mechanism of the reaction between haloalkanes and CN-?

A

Nucleophilic substitution.

41
Q

Describe the mechanism of the reaction between haloalkanes and CN-.

A

The CN- nucleophile attacks the polar C-X bond, forming a new covalent bond between the two C atoms to give a nitrile and displacing an X- ion.

Chemistry (13 decks)

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