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LMZ/CHEM109A/ Winter 2010

II. Elimination and rearrangement reactions of alcohols

1. Acid catalyzed dehydration of alcohol to alkene (Sec. 10.4)

(3>2>1)

mechanism?

-carbocation rearrangement may occur

- SN2 reaction competes with E2 dehydration

2. Dehydration by POCl3

III. Oxidation of alcohols, aldehydes, and thiols

A. Oxidation of alcohols and aldehydes (Sec. 10.5)

R C

OH

H

H

R H

O[O], oxidation

1 alcohol

R OH

O

aldehyde carboxylic acid

[O]

a. Oxidation of 1 alcohols to aldehydes or carboxylic acids

N HCrO3Cl

pyridiniumchlorochromate (PCC)

e.g. Na2Cr2O7, H2O,

ethanolOr Jone's reagent

(CrO3, H3O+, acetone)

OR KMnO4, H2O

e.g. Na2Cr2O7, H2O, ethanol, OR CrO3, H3O+, acetone, (OR KMnO4, H2O)

[O], oxidation

(CrO3, pyridine, HCl)

R C

OH

R'H R R'

O[O], oxidation

2 alcohol ketone

b. Oxidation of 2 alcohols to ketones

e.g. PCC, CH2Cl2OR Na2Cr2O7, H2O, ethanol

OR CrO3, H3O+, acetone

[O]

no furtheroxidation

R C

OH

R'

R"

[O], oxidation

NO REACTION

c. 3 alcohols cannot be oxidized

3 alcohol

mechanism:

IV. Amines as organic bases (sec. 10.6)

- amino (NH2-or NR2

-) is a very poor leaving group;

- amines does not undergo elimination or substitution reactions on the C-N bond.

- as base


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V. Nucleophilic substitution reactions of ethers (ROR)

A. RO-is poor leaving groups similar to OH

-: need acid activation

B. SN1 or SN2 mechanism (PCl3or TsCl not working)

VI. Epoxide (one kind of ether) ring opening (sec. 10.8)

A.Due to ring strain, much more reactive than normal ethers

B. under acidic conditions-- opened by halide, even H2O and ROH

- reaction proceeds with neither pure SN2or SN1.

- regioselectivity:

D.basic conditions:

- regioselectivity controlled by sterics

- stereochemistry: SN2

VII. Crown ethers

- help dissolve metal cations

- Na+--- [15]-crown-5

- K+

-----[18]-crown-6- Li+----[12]-crown-4


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IX. Thiols, sulfide (sec. 10.11)

A. naming thiols- as the principle functional group, alkane + thiol (similar to alcohol case)

- naming priority: OH>SH>NH2, when treated as substituent, use 'mercapto'

B. naming sulfide: (similar to ether)

C. Strong nucleophiles due to high polarizability (softness)

X. Organometallic compounds (sec. 10.12)A. compare:

B. Organolithium compounds: prepared in alkanes- strongly basic (pKa>40), can be nucleophile as well

- C-Li bond: polarized covalent bond (not ionic bond)

C. Organomagnesium compounds -- Grignard reagents (in ethereal solvent)

- strongly basic, but less reactive than corresponding lithium compounds.

- C-Mg bond: polarized covalent bond, not ionic bond.

D. Reactions:

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