Reagents for reducing carbonyl groups

NaBH4

reacts only with aldehydes and ketones

LiAlH4

non selective, reacts with all carbonyl groups, use ether as solvent

Mechanism:

1. one of the bonds in C=O attack the oxygen and the bond of H—Al attacks the carbon,

2. O (-) attacks the H in H3O

Catalytic hydrogenation of ketones and aldehydes

not selcetive, reduces cdbo and cdbc,

Raney Ni/H2, makes alkanes and alcohols

organometallic reagents for alcohol synthesis

• grignard

• organolithium

  Both work the same way, ron each reagent attacks c that is double bonded to O, then double bond attacks O to make single bond. The H2O is used to deprotonate

organomettalic reagent with ethylene oxice

R attacks one of the corners of the trial and that bond attacks O, leads to a longer chain. Final step is to protonate to make O into OH.

Dehydration of alcohols

Removes OH bonds. an use H2SO4 as an E1mechanism to make alkenes. With Primary alcohols, hydride shift is necessary to make more substituted alkene.

POCl3 can also be used as a dehydration agent to convert alcohols into alkenes in a more controlled manner, typically resulting in fewer carbocation rearrangements. It follows hoffman rule making alkeen on the less substituted carbon.

• mechanism:

  1. alcohol lone pairs attack P and P double bond to O attacks O on P

  2. Negative charged O attacks P back to make O double bond P again while 1 Cl leaves

  3. pyridine attacks H on the OH and bond attack O back

  4. Pyridine attack H on attached to adjecent caaarbon from C—O and the H bond attacks the bond from C—C bond to form alken

  5. O2PCl2 leaves