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Organic Chemistry Chapt 10 Organohalides
Properties of alkyl Halides, radical halogenation, allylic bromination, resonance revisited, preparing alkyl halides from alcohols, grignard reagents, and oxidation reduction
28
Chemistry
Undergraduate 2
11/15/2011

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Term

 

What are organohalides?

Definition
compounds that contain one or more halogen atoms
Term



A reaction is an oxidation if....


Definition

if it results in

(a) an increase in the number of bonds between carbon and an element more electronegative than carbon (for example, O, N, a halogen) or

(b) a decrease in the number of bonds between carbon and a less electronegative element (most often H, but also B, Mg, etc.). 

Term


A reaction is a reduction if it results in

Definition

 (a) a decrease in the number of bonds between carbon and an element more electronegative than carbon or

(b) an increase in the number of bonds between carbon and a less electronegative element, most frequently H.

Term

 

What are the rules for oxidation state of Carbon?

Definition
A bond to H contributes –1 to the oxidation state of C. (The same is true for any atom less electronegative than C.)
A bond to O, N, or halogen contributes +1 (as does a bond to any element more electronegative than C.)
A bond to C contributes 0.
Term
If the oxidation level of carbon (sum of oxidation states) increases, the reaction is an......
Definition

 

Oxidation

Term
If the oxidation number of a carbon decreases in  a reaction the reaction is an.....
Definition

 

 

Reduction 

Term
When naming alkyl halides you number the carbons of the parent chain at the end nearer the first substituent of a alkyl or halo?
Definition
Either or..if the first sub. is a alkyl or halo you start numbering from whichever is first
Term
If two substituents are at the same distance from either end you must.....
Definition
*number in alphabetical order
Term

 

Radical Halogenation of alkanes is not a good method of producing alkyl halide because.....

Definition
a mixture of products is obtained
Term
What is an allylic position?
Definition

It is the position NEAR a double bond. 

[image]

* = allylic positions

Term
NBS in the presense of light (hv) creates an alkyl halide from a alkene by..
Definition

addition of Br at the allylic position

 

*occurs by radical chain reaction

*Br radical abstracts an allylic hydrogen forming a allyic radical AND HBR

*HB2 then reacts with  NBS to form Br2  which reacts with allylic radical  & Br radical 

(PAGE 284)

Term
Why does bromination with NBS react at the allylic postion?
Definition

Due to bond dissociation energies.  

 

*Allylic(370 kj/mol)  has lower bond strength then alkyl [CH3 sp3](410 kj/mol) and vinylic[double bonded C sp2] (465 kj/mol)


*Therefore allylic radicals are more stable and favorable

Term

Which order of stability is this?

 

Vinylic<methyl<primary<secondary<tertiary<allylic

Definition

 

in order from least to greatest stability

Term
Allylic Radicals are symmetrical so they have 2 resonance forms which consist of....
Definition

 1. with unpaired electron on the left and double bond on right

2. with unpaired electron on right and double bond on left


[image]

Term

 

The greater the number of resonance structures an allylic radical can have ..............

Definition

 

 

The more stable it is

Term
A allylic radicals are stable because the electrons are delocalized which means..
Definition
electrons are spread out over extended Pi orbital rather then localized at one site.
Term
allylic bromination of unsymmetrical alkenes gives a mixture product..which end is most favored?
Definition

 

Primary End

(C bonded to one other C and 2 H)

Term
Preparing alkyl halides from alcohol work best with Primary, secondary, or tertiary alcohols?
Definition

 

 

Tertiary Alcohols

 

(primary and secondary act more slowly)

Term
OH on tertiary Carbon with react with what to give a alkyl halide?
Definition

 

H-X & Ether at 0 degrees celsius

 

(Halogen replaces the OH)

Term
What two reagents interact with primary and secondary alcohols? What to they do?
Definition

SOCl2 & pyridine (replaces OH with Cl)

PBr3 & Ether 35 deg C  (replaces OH with Br)

[(Ch3Ch2)2NSF3] HF & Pyridine(replaces OH with F)

 

 

 

Term

 

Grignard Reagents are..

Definition

the products of alkyl halides reacting with Magnesium Metal in Ether or THF


*aka alkylmagnesium halides

 

* example of organometallic compound b/c of carbon metal bond

Term

What are the products of?

CH3CH2CH2Br----->Mg/ether------->H20

Definition

1.CH3CH2CH2MgBr (Mg goes between C and X)

 

2.CH3CH2CH3 (Water destroys Mg)

Term
Grignard Reagent can also be used to convert an alkyl halide to  an...
Definition
Alcohol
Term

 

 

Alkyllithium Reagents created by

Definition
alkylhalide reacting with lithium metal and are very strong nucleophiles and bases
Term

 

What is the product? 

CH3CH2CH2CH2Br----->2 Li

Definition

 

CH3CH2CH2CH2Li + LiBr

Term
What are Gilman Reagents?
Definition
When alkyllithiums react with copper(I)Iodide in ether solvent to form lithium dialkylcopper (gilman reagent)
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