Study Guide 7 ochem

Describe how E-Z notation is used in the naming of stereoisomeric alkenes when

Z Configuration= High priority substituents are on the same side of the double bonds.

E Configuration=High-priority substituents are on opposide sides
of the double bond

What are the Cahn-Ingold-Prelog Priority rules?

Atoms are ranked by their atomic number to see which one have the higher priority. The the molecule will rotate 1-2-3. CW=R CCW=S.

In chiral centers the lowest priority has to be in the back, if not, the configuration is reversed.

In double bonds atoms are direclty attached to each carbon ranked by their atomic number, they can be 1 or 2 if both are on the same side is Z if they are on opposite ends is E.

What is your explanation for how C-C double bonds are formed?

C=C double bonds equal the sp2 hybridized and are formed from the overlap of 2 sp2 hybridized orbital that are sigma bonds.
and the two P orbitals overlap to form pi bonds.

What is the importance of Zaitsev’s rule?

the importance of the Zaitsev s rule is that it summarizes the idea that beta elimination reactions are regioselective and will prefer to form the most substituted and more stable alkene as s major product

What are the criteria for determining the stability of an alkene?

degree of substitution
van der Waals strain in cis-stereoisomers
chain branching- the more branched the more stable that unbranched.

What is the difference between an E1 and an E2 mechanism in alcohol
dehydration?

E1:
rate low= K(Rx)
rate determining state is unimolecular, only in alkyloxonium ion
3 and 2 usually
carbocation formation and rearrangement

E2 :
rate low= k (Rx) (BASE)
rate determining step bimolecular- alkyloxonium ion and water
1 usually
no carbocation formation

Why is β-elimination called β-elimination?

B elimination is called β-elimination because the sigma beta are adjacent to pair of electrons that are leaving the group will form a new pi bond.

When we say that a reaction is stereoselective what do we mean?

Stereoselective reactions mean when a reaction gives two or more stereoisomeric products but prefers one over the
rest

Name two ways by which a carbocation may undergo rearrangement.

alkyl group migration- methyl shift
hydride shift

Explain why some carbocations undergo rearrangement

some carbocations undergoes rearrangements because organic molecules will do whatever they have to do to become stable, therefore they create more stable carbocation.

What is the mechanistic role of H2SO4 in the following reaction? Explain.

H2SO4 will catalyze the reaction and therefore increase the rate of the reaction of the reaction.

What is the difference between regioselectivity and stereoselectivity? Support your answer with examples

regioselectivity: rxns proceeds in more than one direction before direction is preferred.

stereoselectivity: single starting material yields with 2 or more stereoisomeric products but gives one in greater amount. cis vs trans.

state what is meant by anti-elimination? Support your answer with an example.

Anti-elimination describes stereospecificity which is the inversion of the stereochemistry of the reactant. It gives a specific product from a certain product.

What do we mean when we say that a mechanism is a concerted process

we mean to say that the mechanism bond changes( bond breaking and bond making ) all happens in one step such as in E2 and Sn2 bimolecular steps.

Give an example which shows how hydride shifts occur.

hydride shift occurs to give a better/stable version of a carbocation