Organic Chemistry Chapt 10 Organohalides

 

What are organohalides?

compounds that contain one or more halogen atoms



A reaction is an oxidation if….


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.). 


A reaction is a reduction if it results in

 (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.

 

What are the rules for oxidation state of Carbon?

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.
If the oxidation level of carbon (sum of oxidation states) increases, the reaction is an……

 

Oxidation

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

 

 

Reduction 

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

 

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

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

It is the position NEAR a double bond. 

[image]

* = allylic positions

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

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)

Why does bromination with NBS react at the allylic postion?

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

Which order of stability is this?

 

Vinylic<methyl<primary<secondary<tertiary<allylic

 

in order from least to greatest stability

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

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

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


[image]

 

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

 

 

The more stable it is

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

 

Primary End

(C bonded to one other C and 2 H)

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

 

 

Tertiary Alcohols

 

(primary and secondary act more slowly)

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

 

H-X & Ether at 0 degrees celsius

 

(Halogen replaces the OH)

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

SOCl2 & pyridine (replaces OH with Cl)

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

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

 

 

 

 

Grignard Reagents are..

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

What are the products of?

CH3CH2CH2Br—–>Mg/ether——->H20

1.CH3CH2CH2MgBr (Mg goes between C and X)

 

2.CH3CH2CH3 (Water destroys Mg)

Grignard Reagent can also be used to convert an alkyl halide to  an…
Alcohol

 

 

Alkyllithium Reagents created by

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

 

What is the product? 

CH3CH2CH2CH2Br—–>2 Li

 

CH3CH2CH2CH2Li + LiBr

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