Alekenes and Alkynes Organic OAT

Hydrohalogenation rxn (addition of HX to an alkene)

The H goes on the C with the most amount of H’s on it. The halogen goes on the one with fewer H’s

In hydrohalogenation why does the hydrogen bond to the carbon with the most H’s?

Carbocation Stability

Primary carbocation NEVER FORM. They are far to unstable.

What is carbocation stability

CARBON CATIONS are more stable as they have more carbons attached to them.

Primary Allyl’s have resonance.

Markovnikov Products

The alkene addition product that comes from the most stable carbocation intermediate.

1,2 Hydride Shifts (carbocation rearangments)

Essentially, if a hydrogen can shift a carbocation into a more stable carbocation by adding itself, it will do so.

• This cannot be done to do a equal carbocation stability
  

KEEP IN MIND THIS CAN ONLY HAPPEN IF THE HYDROGEN IS DIRECTLY NEXT DOOR.

1,2 Methyl Shift (carbocation rearrangments)

Essentially, if a methyl can shift a carbocation into a more stable carbocation by adding itself, it will do so.

• This cannot be done to do a equal carbocation stability

KEEP IN MIND THIS CAN ONLY HAPPEN IF THE HYDROGEN IS DIRECTLY NEXT DOOR.

C ring expansions (carbocation rearrangments)

• Why does it happen?

Usually done to relieve angle strain (any rings not in 5 or 6)

C ring expansions (carbocation rearrangments) : mech

Acid Catalyzed Hydration

It’s intermediates CAN undergo carbocation rearrangements if it INCREASES stability.

This can be good or bad.

Oxymercuration - demercuration

USED for Acid catalyzed hydration reactions:
SINCE: It’s intermediates CAN undergo carbocation rearrangements if it INCREASES stability.

SO INSTEAD:
A reaction that does the same thing as acid catalyzed hydration without the rearrangements.

BOTH ARE STILL MARKOVNIKOV (we are only avoiding a carbocation rearrangment)

Acid Catalyzed Alcohol Addition

Adding Halogens (X₂) to alkenes

Always ANTI

NO REARRANGMENTS DUE TO RINGED HALOGEN INTERMEDIATE

Adding Halogens (X₂) and H2O to alkenes

Since H2O is the solvent, there is SO much more of it in the system

NO REARRANGMENTS DUE TO RINGED HALOGEN INTERMEDIATE

Adding Halogens (X₂) and ROH to alkenes

R = carbon chain or ring

THERE is SOOO much more of HOR in the system (it is the solvent)

Antimarkovnikov?

Adding a reagent to the position that is not Markovnikov (most stable carbocation)

Hydroboration-Oxidation

They end us sys (not anti)

(same direction)

BH3/THF

Hydrobromination with peroxide

Antimarkovnikov

NO REARRANGMENTS

Peroxy Acid

another example is mCPBA

Epoxidizing Alekenes

Adding a peroxyacid to an alkene to make it into an EPOXIDE

Adding nucleophiles to an epoxide (both acidic and basic conditions) (with variability)

Under basic Conditions: Gets added to the carbon with least interference.

Under Acidic Conditions: We are going to have the nucleophile attack the most stable carbocation.

Anti-dihydroxylation

Adding nucleophiles to an epoxide basic conditions (even molecule)

anti

Anti-dihydroxilation

Adding nucleophiles to an epoxide acidic conditions (even molecule)

anti

Anti-dihydroxilation

sys dihydroxide

OSO4

Peroxide

Ozonolysis of Alkenes

Treating an alkene with Ozone (O3), it cuts the double bond and puts an oxygen at the end of each half.

But it can vary depending on the workup

Ozonolysis: Workup: Zn, H20 or DMS (CH3)2S

Ozonolysis: Workup: H2O2

1 and ONLY 1 of those extra H’s is replaced with an -OH. (carboxylic acid)

• If there is NO extra H’s you get the same product as in ozonolysis with H2O and Zn or DMS

Ozonolysis using KMnO3 (hot conc) / H3O+

This occurs only to internal alkenes. (alkenes with a carbons on either side of the alkenes.

It does the same ozynolysis reaction.

BUT if it is instead a terminal alkene (has a carbon attatched to an H) then instead it will turn the terminal carbon into CO2.

Alkene ozonolysis with HIO₄

Use of OsO4 to add two sys OH groups

Then you use HIO4! to split them and convert them to aldehydes.

KMnO4 (regular not treated)

Makes a vicinal diol (two OH’s added on an alkene group. )

same as OSO4 and peroxide.

Alkyne Ozonolysis

We end up getting two carboxylic acids instead of ketones.

O3, H2O or H3O+

Basic KMnO4 and H3O+

Gives two carboxylic acids.

Terminal Alkyne Ozonolysis

Forms CO2 and of course a carboxylic acid.

Catalytic Hydrogenation of Alkenes

Breaks rules of traditional alkene addition reactions.

They form a cis product and remove the double bond.

They attatch to a metal and then add cis H’s.

Metals include:

• Pd, Pt, Rh, or Ni catalyst.

Catalytic Hydrogenation of Alkynes

They form a cis product and remove the triple bond all the way to single. (does not stop at alekene)

They attatch to a metal and then add cis H’s.

Metals include:

• Pd, Pt, Rh, or Ni catalyst.

Catalytic Hydrogenation of Alkynes to get to an alekene to get a E alkene

Goes from a triple to an alkene. HOWEVER, it is a Z alkene. (zame zide)

Catalytic Hydrogenation of Alkynes to get to an alekene. (E)

Na or Li

NH3, at low temperatire.

Catalytic Hydrogenation of Alkynes to get to an alekene. (Z)

H2, Lindlar Catalyst

Alkyne Addition Reactions: DEFS of terminal vs internal alkynes

General Alkyne Reactions

Generally Anti (E alkene)

Excess reactions for alkynes

Hydrohalogenation with halogens. (and also what would happen in excess)

Wants to go to carbon with most H’s initially once more.

IF not in an external ALKYNE like this example, the HX reaction will appear in a mixture.

Hydrohalogenation with halogens. (and also what would happen in excess) (internal alkyne)

Still end up on the same side since once the initial reaction occurs, then there will be an H, which is more favorable for the H’s and the X will go with the more substituted one.

DiHalogenation (alkynes)

They will be anti since the Halogen will go toward the interior position.

Remember, it can not be in water or ROH solvent

Dihalogenation (alkeynes)

Remember, it can not be in water or ROH solvent

Hydrobromination with Peroxide (alkynes) (also in excess)

Antimarkovnikov

Acid Catalyzed Hydration (alkynes) terminal

NEED HgSO4

Markovnikov

They then turn to ketones afterward (more stable)

Acid Catalyzed Hydration (alkynes) internal

NEED HgSO4

mixture of products (no defining H)

They then turn to ketones afterward (more stable)

Hydration of alkynes (antimarkov)

BH3 / THF or (Sia)₂ BH * THF

H202, OH-, H2o

INSTEAD of ketone, we get a aldehyde.

Alkylating Alkynes (with a alkylhalide)

The H atoms on the ends of terminal alkynes are sufficiently acidic to allow them to be removed using sodamide (NaNH2)

These can then have an halide added to them to add an alkyl group (or carbon chain)

Alkylation with a ketone

The H atoms on the ends of terminal alkynes are sufficiently acidic to allow them to be removed using sodamide (NaNH2)

Alkyation with an epoxide

Basic conditions shown in image (less substituted)

The H atoms on the ends of terminal alkynes are sufficiently acidic to allow them to be removed using sodamide (NaNH2)

Alkanes to Alkynes

NaNH2 is used to kick out the hydrogen. and subsequent halogens to create an Alkyne

Kinetic Products Organic

KINETIC:

• Forms fastest

• Comes from most stable carbocation intermediate

• Is favored at low temperature (kinetic control)

• -40^o or lower.

Thermodynamic Products Organic

• Forms more slowly

• Favored at high temperature

• Most substituted (most internalized) alkene product, which is the most stable final product (Zaistev’s rule)

Zaistev’s Rule

Two isomeric alkenes, the one with the largest number of non-hydrogens in its c=c double bond is the most thermodynamically stable alkene. (most substitued)

Thermodynamic vs kinetic product determination.