Organic Chemistry Chapt 11

 

 

Alkyl Halides are electrophile or nucleophiles?

 

 

Electrophiles that involve polar reactions with nucleophiles and bases

 

 

What is kinetics?

the relationship between the rate at which a reaction occurs and the concentration of reactancts

 

 

What are second order reactions and what is the formula?

Reactions which the rate is linearly dependent on the concentrations of two species

 

=k x [RX] x [-OH]

 

k=rate constant

RX=CH3Br concentration in molarity

OH=OH concentration in molarity

 

What does Sn2 reaction stand for?

 

 

 

*Short for Substitution, Nucleophilic, Bimolecular (2 molecules take place in the step where kinetics are measured [nucleophile and alkyl halide])

 

 

 

 

How does Nucleophile attack substrate in Sn2 Reaction? What is the outcome?

*This takes place in a single step (no intermediate) 

*Nucleophile attacks from opposite side the halide is on (180 degrees)

*When Nucleophile electrons attaches is forces out the halide causing a transition state where the negative charge is delocalized

 [image]<–Transition state

 

*The back side approach causes the substrate to invert

(R would turn into an S vice versa)

 

 

 

 

In Sn2 Reactions, do they work faster with more or less substrates attached to the carbon being attacked??

the less substrates the faster the reaction

 

***Vinylic and Aryl Halides CAN NOT react in Sn2 Reactions

In Sn2 Reactions…..
A Negative nucleophile = a ______ Product 

 

 

Neutral Product

In Sn2 Reactions…
A Nuetral nucleophile = a _______ product 

 

positive

Nucleophilicity usually increases and you go _______  a column of the periodic table

 

 

 

DOWN

 

 

Negative charged nucleophiles are more or less reactive than neutral ones?

 

 

MORE

What does Sn1 reaction mean? What is its rate equation?

 

stands for subtitution nucleophile unimolecular

 

*It is a first order process which means the concentration of the nucleophole does not appear in the rate equation

=k x [RX]

 

What is the highest transition state of energy in a Sn1 rxn called?

 

Rate limiting step or rate determining step

How does an Sn1 reaction occur?
the leaving group leaves first, a carbocation intermediate is formed, the the nucleophile approaches leading to a racemic mixture of product enantiomers. 

 

 

What does Benzylic mean?

means next to a aromatic ring
Sn1 reactions prefer tertiary or secondary substrates?
 tertiary

 

What solvents are preferred in Sn1 reactions?

 

polar protic solvents 

(alcohols, waters and so on)

 

*affects on rxn due to stabilization or destabilization of transtion state

 

What happens during elimination reactions of alkyl halides?

Hydrogen halide is eliminated from alkyl halide to form an alkene
What is Zaitevs rule?

According to Zaitsev’s rule, during elimination of HX from an alkyl halide, the more highly substituted alkene product predominates.

E2 reactions are….

 stands for : elimination bimolecular

 

*alkyl halide treated with a STRONG base [-OH or RO-]

 

*there is no intermediate, acts like Sn2 and perfers antiperplanar  (all 4 reacting atoms lie in the same place but H and X are anti each other) 

*antiperplanar preferred because of Staggered realtion ship

 

What is the rate equation of E2 reaction?

 

Rate= k [base][substrate]

What is the E1 rxn and what the the rate formula

·        **Elimination of HX occurs by E1 mechanism if the alkyl halide is treated with a weak base or a non-basic nucleophile.

·      ***  An intermediate carbocation is generated in the process.
***rate  = k[substrate]

str

 

 

What is E1cB rxn?

·        Takes place through a carbanion intermediate

·        Reaction common in substrates with poor leaving group, e.g. OH, two carbons away from a carbonyl group.

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