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chemistry > Chapter 26 - Carbonyls and Carboxylic Acids > Flashcards

Chapter 26 - Carbonyls and Carboxylic Acids Flashcards

Carbonyl compounds, Identifying aldehydes and ketones, Carboxylic acids, Carboxylic acid derivatives.

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1
Q

What is the double bond in the carbonyl and alkene functional group made of?

A

A σ (sigma) bond and a π bond.

The sigma bond is formed by the direct overlap of orbitals between the C and O atoms. The pi bond is formed by the carbon and oxygen p orbitals - sideways overlap above and below the atoms.

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2
Q

What are the two carbonyl groups?

A

Aldehydes and Ketones

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3
Q

What is the carbonyl functional group?

A

C=O

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4
Q

What is an aldehyde? How are they named?

A

Aldehydes have the functional group CHO and a suffix of ‘al’.

H-C=O

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5
Q

What is a ketone? How are they named?

A

A ketone ends in the suffix ‘one’ and functional group is CO
looks like this:
C
C=O
C

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6
Q

What is the reaction and conditions for oxidation of aldehydes?

A

Reflux
with a K2Cr2O7 / H+ catalyst
(+ oxidising agent)

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7
Q

Outline the detection of a carbonyl group? How do you ID the solid?

A

To detect carbonyl (C=O) compounds:
- Add 2,4 DNP
- If a yellow/orange precipitate forms - indicates a carbonyls presence

To ID the solid:
= filter ppt, recrystalise, take m.p. and compare to known values

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8
Q

Which reagent can distinguish between an aldehyde and a ketone?
What occurs?

A

Tollen’s reagent - reacts with an aldehyde only.
A silver mirror forms.

Ag+(aq) + e- –> Ag(s)

Aldehydes are oxidised to carboxylic acids. Ketones cannot be oxidised further.

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9
Q

When is the double bond (=) polar or nonpolar?

A

1) The C=C ( alkene group) is non polar
2) The C=O (carbonyl group) is polar

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10
Q

How are aldehydes reduced and what to?

A

Aldehydes are reduced by NaBH4 to primary alcohols.

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11
Q

How are ketones reduced and what to?

A

Ketones are reduced by NaBH4, to secondary alcohols

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12
Q

Outline the reaction mechanism for nucleophilic addition of NaBH4 to carbonyl compounds?

A

BH4- —> H- +BH3 (H- = nucleophile)

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13
Q

Outline the reaction of carbonyl compounds with HCN? What are the conditions?

A

HCN adds across the C=O bond of aldehydes and ketones to form a hydroxynitrile (containing a -OH and -CN functional groups)

HCN is made from sodium cyanide NaCN and sulfuric acid H2SO4.

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14
Q

Outline the mechanism for a carbonyl compound reacting with NaCN/H+ ?

A

in this reaction, the nucleophile is the cyanide ion, :CN- ( from the NaCN)

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15
Q

How can acidified potassium dichromate (K2Cr2O7/H+) distinguish between aldehydes and ketones?

A

Aldehyde present - Orange to green.
Ketone present - no change to solution (remains orange).

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16
Q

Why is potassium cyanide used instead of hydrogen cyanide?

A

It’s safer. HCN is a poisonous gas.

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17
Q

How soluble is carboxylic acid?

A

The C=O and O-H bonds in carboxylic acid are polar allowing it to form hydrogen bonds with water.

1) carboxylic acids are only soluble up to 4 carbon atoms
2) solubility decreases as carbon chain increases because the carbon chain is non polar
3) Dicarboxylic acids are even more soluble.

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18
Q

How strong are carboxylic acids?

A

Carboxylic acids are weak acids and only partially dissolve in water

RCOOH (aq) = H+ + RCOO-

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19
Q

Carboxylic acid + metal = ?

A

in aqueous solution carboxylic acids react with metals to form a carboxylate salt and hydrogen gas.

e.g 2CH3COOH (aq) + Mg(s) = (CH3COO-)2 Mg2+ + H2 (g)

20
Q

Carboxylic acids + metal oxides =?

A

carboxylic acids react with metal oxides to form a salt and water.

e.g 2CH3COOH + MgO = (CH3COO-)2Mg2+ + H2O

21
Q

Carboxylic acids + alkalis = ?

A

carboxylic acids react with alkalis to form a salt and water

e.g CH3COOH + NaOH = CH3COO-Na+ + H2O

22
Q

Carboxylic acid + carbonates = ?

A

carboxylic acids react with carbonates to form a salt, CO2 and H2O

e.g 2 CH3COOH + Na2CO3 = 2CH3COO-Na+ + CO2 + H2O

23
Q

Name the four carboxylic acid derivatives

A

1) Ester
2) Acyl chloride
3) Acid anhydride
4) Amide

24
Q

How do you name esters?

A

1) ‘oic acid’ suffix is removed and replaced with ‘oate’
2) The alkyl chain attached to the -O is then added to the first word

25
Q

What is esterification? Conditions?

A

Esterification is the reaction of an alcohol with a carboxylic acid to form an ester (RCOOR)

An Alcohol is warmed with carboxylic acid + conc H2SO4 (catalyst)

26
Q

What is hydrolysis ?

A

The chemical breakdown of a compound in the presence of water or in an aqueous solution.

27
Q

What is alkaline hydrolysis of an ester? What are the conditions, reagents and products?

A

Alkaline hydrolysis is irreversible. The ester is refluxed with aqueous alkali.

  1. Ester heated under reflux with aqueous alkali (hydroxide ions )
  2. Ester is broken down by water into carboxylate ion and alcohol
28
Q

What is acid hydrolysis of an ester? What are the conditions and products?

A

Acid hydrolysis is the reverse reaction of esterification

  1. Ester is heated under reflux with dilute aqueous acid
  2. Ester broken down by water into carboxylic acid and alcohol
29
Q

How do you name an acyl chloride (-COCl)?

A

Replace ‘oic acid’ with ‘oyl chloride’

30
Q

How do you name an acid anhydride?

A

Change ‘-oic acid’ to ‘-oic anhydride’

31
Q

When an acid anhydride reacts with a nucleophile, what are the two products?

A

R-CONu
R-COO-

32
Q

Name the characteristic mechanism to change an acyl chloride to a carboxylic acid?

A

Addition-Elimination

33
Q

How to prepare an acyl chloride?

A

Carboxylic acid + Thionyl chloride (SOCl2)

34
Q

Acyl chloride + alcohol = ?

A

Ester + HCl

35
Q

How to form esters from acyl chlorides?

A

acyl chloride + alcohol = aliphatic ester + HCl

acyl chloride + phenol = aromatic ester + HCl

36
Q

How to form carboxylic acids from acyl chlorides?

A

acyl chloride + water –> carboxylic acid + HCl

37
Q

How to form amides from acyl chlorides?

A

acyl chloride + ammonia (NH3) –> primary amide + NH4+Cl-

acyl chloride + amine (R’NH2) –> secondary amide + R’NH3+Cl-

38
Q

How do acid anhydrides react with alcohols, phenols, water, ammonia and amides?

A

In the same way acyl chlorides do

39
Q

Whats the equation for for the formation of phenyl ethanoate?

A
40
Q

What’s the carboxyl group?

A

A carbonyl group + hydroxyl group= carboxyl group.

carboxyl group is COOH O=C-OH

41
Q

Whats an ester? How do you name it?

A

where a carboxylic acid’s H in the OH group is replaced by C making a C-O-C bond.

Named after its parent carboxylic acid.
To name an ester remove the suffix -oic acid and replace it with ‘-oate’

42
Q

What is an acyl chloride? How do you name it?

A

In an acyl chloride the OH in a carboxylic acid is replaced by a Cl group to become O=C-Cl .

Named after its parent carboxylic acid from which its derived.
To name: remove the ‘oic acid’ suffix and replace it with ‘oyl chloride’

43
Q

What is an acid anhydride? How do you name it?

A

An acid anhydride is when two carboxylic acids are sharing an O instead of having an OH group.

Named by removing the ‘acid’ and putting the suffix ‘anhydride’.

44
Q

Whats an amide?

A

An amide is when the OH group on a carboxylic acid is replaced by an ‘NH2’.
O=C-NH2

45
Q

whats an Ether?

A

Ether has a functional group COC

46
Q

whats a Dimer?

A

A structure containing two identical or similar units

47
Q

Describe the recrystalisation practical.

A
  • Dissolve solute in minimum vol of boiling solvent.
  • Cool the solution at room temperature and then put beaker in an ice bath. Slow cooling leads to purer crystals.
  • Crystals filtered through Buchner funnel and dry.
  • Melting point can be can be determined to see how pure the crystals are or to identify the substance.

chemistry (22 decks)

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