aldehydes + ketones

if C=O at end of chain?

aldehyde (-al)

if C=O in middle of chain?

ketone (-one)

how are aldehydes and ketones attracted to themselves?

cannot H bond, attracted by permanent dipole forces

why are smaller ones soluble in water?

can form H bonds w/ water

why dont they undergo addition reactions easily?

the C=O its stronger than C=C

what does potassium dichromate oxidise primary alcohols into?

aldehydes

or further into carboxylic acids

what does potassium dichromate oxidise secondary alcohols into?

ketones

what does potassium dichromate oxidise tertiary alcohols into?

doesn’t oxidise

how is an aldehyde turned into a carboxylic acid?

potassium dichromate + dilute sulphuric acid

via reflux

orange → green

tests for aldehydes?

tollens reagent and fehlings solution

how is tollen’s reagent made?

via aqueous ammonia + silver nitrate contains [Ag(NH3)₂]⁺ ion

how is tollen’s used to test for aldehyde?

heat gently with substance

will oxidise aldehydes into carboxylic acids

silver mirror forms

ketones dont react

why does a silver mirror form when aldehyde present with tollens reagent?

silver ions are reduced to silver atoms

how is fehling’s solution used to test for aldehydes?

heat gently w substance

aldehydes oxidised into carboxylic ciders

blue → red

ketones dont react

why is blue → colour change present when aldehyde reacts with fehlings solution?

fehlings contains blue Cu2+ ions

copper (II) ions reduced to copper (I) oxide

what agents are used to reduce aldehydes/ketones into prim/sec alcohols via nucleophillic addition?

NaBH4

LiAlH4

sources of :H- attracted to the partially negative C

how can carbonyls be reduced?

catalytic hydrogenation

hydrogen + nickel catalyst used

high pressure

addition of hydrogen cyanide?

forms hydroxynitriles

KCN + dilute H2SO4 (source of CN- and H+)

room temp + pressure

naming hydroxynitriles?

CN becomes part of main chain, and the first carbon

why is KCN used over HCN?

HCN can be used, but is toxic + hard to contain

but both are still toxic due to presence of CN-

what happens when carbonyl group in aldehydes or unsymmetrical ketones is planar?

equal chance of attack from both sides

50% of both enantiomer forms

forming racemate mixture

w/ no optical activity