Carbonyls Flashcards
Is there any numbers when naming aldehydes?
Only when di
When is there numbers in ketones?
When the chain is more than 5 carbons/when it’s di
What must you remember when it’s di?
Must keep the e before the number
eg pentane-2,4-dione or butane-1,4-dial
What is the general formula of carbonyls?
CnH2nO
How do you describe pi bonds for C-O?
P orbitals on adjacent carbon and oxygen atoms overlap sideways forming a pi bond above and below the line between the nuclei of the bonded atoms
What are some features of the C-O pi bond?
Localised electrons
High electron density
Reacts with nucleophiles because polar bond means Cdelta+ attracts them
What reactions can the C=O do?
Addition (double bond) Nucleophilic addition (Cdelta+ attracts nucleophiles)
What reagent tests for primary/secondary alcohols, aldehydes and methanoic acid?
H+/Cr₂O₇²⁻
Heat
What does H+/Cr₂O₇²⁻ and heat test for?
Primary/secondary alcohols, aldehydes and methanoic acid
Why does H+/Cr₂O₇²⁻ test for methanoic acid but no other carboxylic acids?
There’s 1 H on the C in the functional group bit in methanoic acid
What is the positive result from H+/Cr₂O₇²⁻
Orange solution goes to a green solution
What does the reagent 2,4-DNPH and sulfuric acid test for?
C=O in aldehydes and ketones
What reagent tests for C=O in aldehydes/ketones?
2,4-Dinitrophenylhydrazine (2,4-DNPH)
Sulfuric acid
What is the positive result for 2,4-DNPH?
Yellow/orange precipitate
What does the reagent Tollen’s and heat test for?
Aldehydes
What tests for just aldehydes?
Tollen’s and heat
What is the positive result for Tollen’s?
Silver mirror will form
What is the equation for H+/Cr₂O₇²⁻?
6e⁻ + Cr₂O₇²⁻ + 14H⁺ -> 2Cr³⁺+7H₂O
How do you use the colour of H+/Cr₂O₇²⁻ to prove something has been oxidised?
Cr₂O₇²⁻ is green and Cr³⁺ is orange and it has been reduced.
In order for it to be reduced something else must have been oxidised.
How do you make ammoniacal silver nitrate?
Mix AgNO₃ + NaOH -> Brown ppt Ag₂O Dissolve ppt in NH₃ to make Tollen's Mix aldehyde + Tollen's + heat Aldehyde goes to silver mirror Ag⁺(aq) +e- gets reduced to Ag(s) Aldehyde gets oxidised to carboxylic acid
What is the equation for Tollen’s?
Ag⁺(aq) + e- -> Ag(s)
How do you distinguish between the precipitates made by 2,4-DNPH?
Use the melting point of 2,4-DNPH derivative Filter (impure) Recrystalise (purify) Filter Leave to dry Collect melting point Compare to a database of known values
What are ketones reduced to?
Secondary alcohols
What are aldehydes reduced to?
Primary alcohols
What reagent is used to reduce carbonyls?
NaBH₄
never in equations - Source of H-/hydrides
What mechanism is done with carbonyls?
Nucleophilic addition
How do you make HCN?
In situ
NaCN + H₂SO₄ -> HCN + NaHSO₄
What is used to do the nucleophilic addition mechanisms?
H- + water
-CN + H+
