AALDEHYDES AND KETONES

Aldehydes and ketones are both carbonyl compounds

both contain the C=O carbonyl functional group

aldehyde carbonyl group

ON THE ENDDDD

Ketone carbonyl group

IN THE MIDDLE

NaBH₄ is a reducing agent

which can convert aldehydes and ketones back into primary and secondary alcohols

LiAlH4 (still strong but abit weaker)

also reduces aldehydes and ketones to their respective alcohols

the mechanism of aldehydes/ketones into alcohols is

NUCEOPHILIC ADDITION

nucleophilic addition of aldehydes/ketones to make alcohols

• C=O bond is polar

  • Cð+ and attracts the negative lone pair of electrons on H-

• H- attacks positive C and donates it alone pair electrons forming a bond with C

• this causes 1 bond between carbon and oxygen to break giving oxygen a lone pair of electrons

• oxygen donates its lone pair of electrons to a H+ ion (from water)

• forming an alcohol

hydroxynitriles are:

• molecuels containing a hydroxyl group OH

• and nitrile group CN

hydroxynitrile suffix

-NITRILE

aldehyde/ketone + potassium cyanide, dilute acid→ hydroxynitrile

ANOTHER NUCEOPHILIC ADDITION

nuceophilic addition of aldehydes/ketones to make hydroxynitriles

• potassium cynide is an ionic compound

• potassium cyanide dissociates in water to form K+ Ions and CN- ions

• KCN⇄K⁺ + CN-

• CN- attacks partially positive carbon and donate a pair of electrons forming a bond with the carbon

• a pair of electrons from C=O is pushed onto O

• oxygen bonds with H+ (from dilute acid) to form OH hydroxyl group

• and hydroxynitrile is produce

aldehydes/ketones + hydrogen cyanide → hydroxynitrile

double bonds are planar

so when nuceophiles attack they can attack from either above or below the plane of the bond

nucleophiles attacking from each side of the bond will produce

a different enantiomer

nucleophile+ aldehyde/ UNSYMMETRIC ketone →

racemic mixture of hydroxynitriles

risk assesment

• KCN is toxic- done in fume cupboard as there is a risk of HCN gas being released from the solution

• organic compounds are flammable so warm them in a water bath NOT bunsen

iUPAC Vs Common

• meth vs form

• eth vs acet

• prop vs propion

physical properties of aldehydes n ketones

• both colourless

• both soluble in water because of hydrogen bonding

• as the akyl chain increasaes, solubility decreases because akyl chain is non polar and water is polar

like dissolve theory

polar dissolves polar

non polar dissolves non polar

aldehyde preparation reaction

primary alcohol controlled oxidisation and product quickly distilled or carboxylic acid forms

tollens reagent

AgI → [Ag(NH₃)₂]⁺

C=O can be reduces

C=C cannot be reduced

aldehydes MORE reactive than ketones

because there are less akyl groups attached to the functional carbon

C=O is a polar bond

the more δ+ the carbon the more reactive it is

akyl groups have a positive inductive effect

push electrons in bond towards attached carbon

decreasing the δ+ charge

makes the compound less reactive

C=O on the end of aldehydes

so only has 1 akyl group attached to functional carbon

C=O in the middle of ketones

so has 2 akyl groups attached to functional carbon