SME 6.2 Carbonyl Compounds

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22 Terms

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What is a carbonyl compound?
an organic molecule that contains a C=O group
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Carbonyl compounds include
aldehydes, ketones, carboxylic acids, esters, amides, acyl chloride and acid anhydrides
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Primary alcohols can be oxidised to form 
aldehydes then further oxidation to carboxylic acids
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The oxidising agents used are acidified potassium or sodium dichromate(VI) (K2Cr2O7 or Na2Cr2O7) which will change colour
from orange to green
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Alternatively, acidified potassium manganate(VII) (KMnO4) can be used, the colour change is from
purple to colourless
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In order to form the aldehyde, distillation apparatus should be used otherwise
the aldehyde will undergo further oxidation
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The aldehyde product has a lower boiling point than the alcohol reactant so
it can be distilled off as soon as it forms
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To form a ketone, which can not undergo further oxidation,
reflux apparatus can be used
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Compounds containing -C=O groups will undergo a condensation reaction with
2,4-dinitrophenylhydrazine
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A condensation reaction is a reaction in which
two molecules join together and a small molecule (such as water or hydrogen chloride is eliminated)
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The positive result for this reaction test is
a deep orange precipitate being formed
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The pos result precipitate can be purified by
recrystallisation
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The melting point of the formed precipitate can then be measured and compared to literature values to find out
which specific aldehyde or ketone had reacted with 2,4-DNPH
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The 2,4-DNPH test is especially useful as 
other carbonyl compounds such as carboxylic acids and esters do not give a positive result
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Aldehydes and ketones have different chemical properties which means
they can be identified
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The carbonyl group in an aldehyde is always situated 
at the end of the chain
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The simplest aldehyde is
methanal, HCHO
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The carbonyl group in a ketone is always situated
in the middle of the chain
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The simplest ketone is
is propan-2-one, CH3COCH3, as you need an alkyl group either side of the carbonyl carbon in a ketone
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In order to determine whether a compound is an aldehyde or a ketone two chemical tests can be performed: 
1) Fehling’s solution

2) Tollens’ reagent
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Fehling’s solution is
a blue alkaline solution which contains copper(II) ions, which act as the oxidising agent
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