Alkene and Alkyne Mechanisms Flashcards
Name this Alkene mechanism
Halogenation (X2 addition)
Name this Alkene overall transformation
Halohydrin formation (X2+H2O/ROH)
Name this Alkene overall transformation
Acid-Catalyzed Addition of Water
Name this Alkene overall transformation
Oxymercuration/Reduction
Name this Alkene overall transformation
Hydroboration/Oxidation
Name this Alkene overall transformation
Catalytic Hydrogenation. Stereospecific. Reduction of alkene to alkane
Name this Alkene overall reaction
Epoxidation
Name this Alkene overall transformation
Ozonolysis
Name this Alkene overall transformation
Cycloproponation
Name this Alkene overall transformation
Hydroxylation
Name this Alkene overall transformation
Oxidative Cleavage of syn-Glycols with HIO4
Alkene is a loose sea of electrons that reacts with a strong acid to break the bond from halide
H-X Addition
What is DCM?
Organic solvent dichloromethane (or methylene chloride) that does not participate in the rxn but gets the compounds into a reactive medium
If Cl and Cl or Br and Br atoms join, what happens to the electrons?
The partial (+) and partial (-) charges (dipole interactions) on both of the highly electronegative atoms will drive the electrons to one side and cause a chemical reaction
What makes this bromonium ring reactive, yet “happy”?
It wants to be broken open The bromonium ring structure is happy because it has a full octet, but it is highly reactive due to the 3-angle ring strain (bond angle about 60 degrees) and all electrons are eclipsed by each other. Also, bromine has a (+) charge. Since bromine is electronegative, so it wants electrons.
Does a bond become a dash or a wedge when you attack the back side of a wedge?
dash
Name this Alkene overall transformation
Halogenation (X2 addition)
What is regioselectivity?
rxn where one constitutional isomer is favored over the other
What is stereoselective rxn?
rxn where one stereoisomer is formed in preference (R/S)
Stereospecific rxn
What time of rxn results in one stereoisomer forming based on the mechanism alone (always san/anti or inversion of stereochemistry
Name this Alkene mechanism
Halogenation (X2 addition)
Halogenation (X2 addition) mechanisms produce a mixture of enantiomers. Why?
The molecule has 2 sigma* bonds (anti) which are empty space that can accept electrons.
Nucleophiles such as Br2 or Cl2 attack with filled MO. To break the sigma bond, you must attack the empty version of the sigma bond which is the sigma* bond. Then, put electrons in empty MO (sigma*).
Why don’t we use F2 or I2 in Halogenation (X2 addition)?
Both work, but F2 is explosive and I2 produces unstable products that decompose readily
Name this Alkene mechanism
Halohydrin formation (X2+H2O/ROH)
In a regioselective rxn, why does the nucleophile attack the more substituted carbon?
Nucleophile attacks the longer, weaker bond. The carbon on the weaker bond can handle the partial charge better because it is the most stable with more substitution and hyperconjugation.
Name this Alkene mechanism
Acid-Catalyzed Addition of Water
When a strong acid and water are mixed completely with an alkene, what is the product?
An alcohol
Properties of Acid-Catalyzed Addition of Water Alkene Mechanisms
- Markov. In the RDS: Acid being added to an alkene (Markov. - proton goes on the carbon with more protons) forming a carbocation
- Intermediate is a carbocation. *Look for carbocation rearrangements (1,2-methyl shift, 1,2- hydride shift, and ring expansion)
- Add water and remove the proton with solvent. Rxn is catalytic in hydronium or proton (does not officially get consumed in the reaction, regenerated in the product). There is a racemic mixture of products if there is stereochemistry on your substrate
H2SO4 + H2O dissociates completely to form
H3O+ (does the chemistry) and HSO4- (spectator)
What is the product of this Acid-Catalyzed Addition of Water Alkene mechanism?
tertiary alcohol
What are the 3 types of Alkene hydration (adding water across an alkene) mechanisms?
- *1. Acid-Catalyzed Addition of Water** - Catalytic. Goes through a carbocation intermediate. First step is an acid addition, Markov.
- *2. Oxymercuration/Reduction** - Goes through mercuronium ring, water attacks the more substituted carbon. No rearrangements. Alcohol ends up where starting alkene was, Markov. Mixture of enantiomers.
- *3. Hydroboration/Oxidation** - Enantiomer of Syn addition of water, anti-Markov. Only + enant if there is stereochemistry
Name this Alkene mechanism
Oxymercuration/Reduction