Organic Chemistry 2 Creating Alcohols

What is an alcohol?

a compound with a hydroxyl group attached

Primary alcohol

has 2 attached H groups, one attached R group

Secondary alcohol

has one attached H group and 2 attached R groups

Tertiary alcohol

Has 3 attached R groups and no H groups

generic reaction

R-OH → RO- + H+

strong base

has a negative charge localized on a heteroatom

ex. C,N,O

more acidic compounds

have multiple resonance structures

Alcohols can be made from

alkyl halide, ester, carboxylic acid, alkene, ketone, aldehyde, ether

Reducing a carbonyl compound to an alcohol

occurs with nucleophilic addition

electrons from H go to C, e- from double bond go to O

O has negative charge, takes H from H3O+

ketones reduce to

a secondary alcohol

aldehydes reduce to

a primary alcohol

What can reduce aldehydes and ketones?

NaBH4, LiAlH4

breaking a pie bond to make a more stable sigma bond

Example ketone reduction

1.) H- bond attacks C in carbonyl, add H to C, break pie bond, e- up to O, O negatively charged

2.) -O grabs H from H3O+, forming secondary alcohol

Example Aldehyde reduction

1.) H bond attacks C, add H group to C in carbonyl, break pie bond, e- up to O, O negatively charged

2.) -O takes H from H3O+, makes primary alcohol

Reducing Carboxylic Acids and Esters

Results in a primary alcohol

2 steps - reduce to carbonyl, ten to alcohol

LiALH4 can reduce carboxylic acid and esters, NaBH4 cannot reduce carb acids or esters

Ester reduction example

1.) H bond from LiAlH4 attacks C, break pie bond, move e- up to O

2.) O- reforms pie bond and kicks off -OCH3 LG

3.) LiAlH4 attacks, re-break pie bond, O- again

4.) react with H3O+ to make OH group

end result = added 2 H groups and one OH

Carboxylic Acid Reduction Example

1.) H attacks -OH part, make pie bond with O, break other pie bond, become O-

2.) O- attacks Al-H3, makes bond, then H from Al-H3 attacks C

3.) OAlH4 groups leaves, H bond forms there instead

4.) react with AlH3 again, H- attacks C, break pie bond with other O, becomes negative charge

5.) O- takes H3O+, becomes OH

Grignard Reagents

charged C group

R-MgX

acts as a strong base, does nucleophilic addition of R group

Mechanism of Grignard Reagent

Example ketone reaction using grignard reagent

R group attacks C where =O is attached

break pie bond, O becomes (-) charged, takes H from H30+

limitations of Grignard reagent

if H is weakly acidic and added to grignard, no rxn will occur

some groups (-CtripleN, -NO2, -SO2R) won’t allow rxn to occur because they will react with girgnard

Turning alcohols into alkyl halides

3’ alcohols will use SN1 reaction

1’ or 2’ alcohols will use SN2 reactions

Sn1 reactions turning alcohols into alkyl halides

• C-O bond breaks, H from HX attached to OH to make H20, good LG

• create carbocation, methyl RAR possible

• -X reacts with carbocation to yield alkyl halide

SN2 reaction to form alkyl halide

PBr3 or SOCl2 (with ether)

backside attack of Br- or Cl- to C, opposite of O LG, rest of molecule attached to O, forms good LG

inverts stereochemistry