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Chemistry module 6 > carbonyl compounds and identifying aldehydes and ketones > Flashcards

carbonyl compounds and identifying aldehydes and ketones Flashcards

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1
Q

What compounds contain the carbonyl functional group

A
  • aldehydes
  • ketones
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2
Q

What is the carbonyl functional group

A

C=O

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3
Q

Describe the structure of an aldehyde

A
  • the carbonyl functional group is found at the end of a carbon chain
  • the carbon atom of the carbonyl group is attatched to one or two hydrogen atoms
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4
Q

What is the structural formula of the aldehyde group

A

CHO

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5
Q

What is the formula of the simplestt aldehyde

A
  • HCHO
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6
Q

Describe the structure of a ketone

A
  • the carbonyl functional group is joined to two carbon atoms in a carbon chain
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7
Q

What is the structural formula of a ketone group

A

CO

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8
Q

what is the simplest ketone and give the formula

A

CH3COCH3
propanone

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9
Q

What is another word for methanala and its use

A
  • formaldehyde
  • used in solution to preserve biological specimens
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10
Q

What is another name for propanone and give its use

A
  • acetone
  • important in industrial solvent and used in nail varnish remover
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11
Q

What is the suffix of an aldehyde group when naming them

A

al

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12
Q

What is the suffix of a ketone when namine them

A

one

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13
Q

Describe the oxidation of aldehydes

A
  • adehydes can be oxidised to carboxylic acids when refluxed with acidified dichromate (VI) ions Cr2O72-/H+ usually as a mixture of sodium or potassium dichromate (VI) K2Cr2O7 and dilute sulfuric acid H2SO4
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14
Q

What is a way of distinguishing ketones from aldehydes

A
  • using potassium dichromate
  • aldehyde will turn green
  • ketones will show no change as they do not undeergo oxidation reactions
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15
Q

Describe the difference of reactivity between carbonyl and alkene functional groups

A
  • C=C double bond in alkenes is non polar
  • C=O double bond in carbonyl is polar
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16
Q

Describe the reactivity of aldehydes and ketones

A
  • it is influenced by the nature of the carbon oxygen double bond
  • oxygen is more electronegative than carbon
  • the electon density in the double bond lies closer to the oxygen atom than the carbon
  • makes the carbon end of the bond slightly positive and the oxygen ened slightly negative
  • due to the polarity of the C=O double bonds aldhydes and ketons react with ome nucleophiles
  • nucleophile is attracted to and attacks the slightly positive carbon atoom reslting in addition across C=O double bond
  • reaction is nucleophillic addition
17
Q

What is NaBH4 and what reaction is it used for

A
  • used as a reducing afent to reduce aldehydes and ketones to alcohols
18
Q

Describe how you turn an aldehyde or a ketone into a into an alcohol

A
  • warming the aldehyde or ketone with NaHB4 reducing agent in an aqueous solution
19
Q

What are aldehydes reduced to

A

primary alcohols

20
Q

W

What are ketones reduced to

A

secondary alcohols

21
Q

Describe the reaction of carbonyl compounds with hydrogen cyanide

A
  • hydrogen cyanide HCN adds across the C=O double bond of aldeydes and ketones
    *
22
Q

Describe why NACN used when reacting HCN with carbonyl compounds

A
  • HCN is colourless and extremely poisonous liquid that boils slightly above room temperature so cannot be used safely in an open larbatory
  • sodium ccyanide and sulfuric acid are used to provide the hydrogen cyanide in the reaction
23
Q

What is the product of an aldehyde reacting with HCN and what are the functioncal groups

A
  • hydroxynitrile
  • -OH
  • Ctriple bond N
24
Q

Why is the reaction of carbonyl compounds and HCL useful

A
  • increasing the length of the carbon chain
25
Q

What does the carbon atom in the C=O bond do

A
  • it is electron defifcient attracting nucleophiles
26
Q

What is the reaction mechanism for aldehydes and ketones

A

nucleophillic addition

27
Q

Describe the mechanism reaction with NaBH4 with a carbonyl group

A
  • the lone pair of electrons from the hydride ion H- is attracted and donated to the positive dipole on the carbon atom in the aldehyde or ketone C=O double bond
  • a dative covalent bond is formed between the hydride ion and the carbon atom of the C=O double bond
  • the pi bond in the C=O double bond breaks by heterolytic fission forming a negativley charged intermediate
  • the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule the intermediate has then been protatnated to form an alcohol
28
Q

Describe the mechanism for the reaction with NaCn/H+

A
  • the cyanide attacks the electron deficient carbon atom in the aldehyde or ketone
  • the lone pair of electrons is attracted and donated to the partial positive chargew on the carbon atom in the aldehyde or ketone C=O double bond a dative covalent bond forms
  • the pi bond in the C=O double bond breaks via heterolytic fission forming a negativley charged intermediate
  • the intermediate is protonated by donating a lone pair of electrons to a hydrogen ion to form the product
  • the product is a hydroxynitrile
29
Q

What is used to detect a carbonyl group

A
  • a solution of 2,4-dinitrophenylhydrazine 2,4-DNP also known as bradys reagent is used to detect the carbonyl functional group
  • a yellow or orange precipitate called 2,4-diitrophenylhydrazone is produced
30
Q

Why is the solid 2,4-DNP dangerous and how do we use it in practicals

A
  • normally used dissolved in methanol and sulfuric acid
  • can be hazardous because of friction or a sudden blow can cause it to explode
31
Q

outline the method for testing for a carbonyl group

A
  • add 5cm depth of a solution of 2,4-dinitrophenylhydrazine to a clean test tube. This is in excess
  • using a dropping pipette add three drops of unknown compounds leave to stand
  • if no crytals form add a few drops of sulfuric acid
  • a yellow/orange preipitate indicates the prescence of an aldehyde or ketone
32
Q

Describe the test to distinguish between aldehydes and ketones

A
  • tollens reagent
  • solution of silver nitrate in aqueous ammonia
  • in prescence of an aldehyde group a silver mirror is produced
33
Q

Describe the method for testing for an aldehyde group

A
  • in a clean test tube add 3cm depth of aqueous silver nitrate AgNO3(aq)
  • add aqueous sodium hydroxide to the silver nitrate until a brwon precipitate of silver oxide Ag2Ois formed
  • add dilute ammonia solution until the brown precipitate just dissolves to form a clear colourless solution - this is tollens reagent
  • pour 2cm depth of the unknown solution into a clean test tube
  • add equal volume of freshly prepared tollen reagent
  • leave the test tube to stand in a beaker of warm water for about 10 to 15 minutes and observed wether any silver mirror is formed
34
Q

Describe how tollens reagent identifies ann aldehyde

A

it contains silver ions which act as an oxidising agent in the precence of ammonia
solver ions are reduced to silver as the aldehyde is oxidised to a carboxylic acid

35
Q

Describe the method for identify an aldehyde or a ketone by melting point

A
  • impure yellow/orange solid is filtered to seperate the solide precipitate from the solution
  • the solid is then recrystallied to produce a pure sample of crystals
  • the metling point of purified 2,4-dinitrophenylhydrazone is measured and recorded
  • the melting pointd id then compared to a database or data table of melting point to identify the original carbonyl compoud

Chemistry module 6 (2 decks)

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