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Organic Chemistry 326 SI
October 31, 2016
Alkyl halide Preparation from alcohols
Organometallic reagents and reactions
Warm up Review
What is the product?
A and D
When reacted with O3 / Zn, H2O, what product(s) form?
A and B
None, this reagent forms epoxides
I and III
I and IV
II and III
II and IV
None of these
* Alkyne reacting with O3 forms carboxylic acids
Radical Reactions (X=Cl, Br, I)
Alkene reactions – Allylic Halogenation
Addition of HX
Addition of X2
NBS / hv, CCl4
Mechanism of Halogenation
Two radicals combine
No new radicals generated
Which molecule(s) forms in the highest concentration?
All but III because of steric hindrance
Replaces a H with X
Radical initiation, propagation, termination
Not very synthetically useful
Produces a mixture of mono, di, tri products
Chlorination produces a mixture of mono-substituted products with the highly chlorinated products
Chlorination vs. Bromination
How many products form from the monochlorination of this alkane?
Hint: Remember to count both constitutional isomers and stereoisomers
Chiral Starting Material Example
Alyllic Carbons and Radical halogenation
What is an alyllic carbon?
Carbon adjacent to a C=C bond
Allyl radical is more stable than a tertiary radical
X2 (Cl2 and Br2)
NBS / hv
All but IV
Key Features of NBS/ hv or ROOR
Adds a Br to the allylic carbon
Can form a mixture of products if the allylic radical has resonance structures
Draw out the resonance structures
What is resonance??
HBr vs. Radical HBr
Forms a carbocation from the addition of H
Must have the more stable carbocation form, therefore the H will add to the less substituted
HBr/ROOR or ∆ or hv
Forms a radical intermediate after the addition of Br•
Must have the more stable intermediate form, therefore the Br• will add to the less substituted carbon
**HCl and HI do not add under radical conditions
Alkyl Halide preparation from alcohols
Which is the starting material?
Preparation from alcohols
HF/pyridine, HCl, HBr, HI
Works best for tertiary alcohols (SN1) (Tomorrow’s lecture)
[(CH3CH2)2NSF3] - diethylaminosulfer trifluoride
Primary and Secondary alcohols (SN2)
What is the SM?
Both I and II
In Organometallic reactions the carbons bear a…
Partial positive charge
Partial negative charge
Full +1 or -1 charge
Metal is more electropositive
They donate electron density to the carbon, therefore, the carbon is more negative
Carbon reacts like a carbanion
=> React as nucleophiles and as bases
Organomagnesium and Organolithium
Very polar carbon-metal bond
Less polar carbon-metal bond
Which product forms?
 2 Li
I and LiOH
II and LiOH
III and LiH
IV and LiH
III, IV and LiH