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Chapter 8 mechanisms

Alkene reactions

TermDefinition
Dehydration Loss of water from an alcohol containing compound; elimination reaction, creates an alkene since OH is taken away (H2O is a by product)
Halogenation Bromine or chlorine adding rapidly to alkenes to form 1,2-dihalides. Occurs with anti stereochemistry (product is trans)
Dehydrohalogenation Loss of HX from an alkyl halide; elimination reaction, creates an alkene since X and H are taken away.
Anti-stereochemistry Two atoms attack from opposite faces, one from top face and one from bottom face; forms a trans compound
Addition of Hypohalous acids The reaction of alkenes with the hypohalous acids HO-Cl or HO-Br to yield 1,2-halo alcohols; occurs indirectly with the reaction of an alkene with Cl/Br in the presence of water. (Alkene + H2O + X2 --> halohydrin + HX) X reduces alkene and leaves a carb
Hydration Water adds to an alkene to form an alcohol (Needs H2O and a strong acid); protonation of an alkene double bond yields a carbo-cation intermediate, which reacts with water to yield a protonated alcohol product, ROH2+
Oxymercuration-demercuration procedure Involves electrophilic addition of Hg2+ to the alkene on reaction with mercury(II) acetate, often abbreviated [Hg(OAc)2] in aqueous (THF) solvent. The inter-mediate compound is then treated with NaBH4, and produces an alcohol. (markovnikov)
Hydroboration Yields a non-Markovnikov product; this reaction involves addition of a BH bond of borane, BH3, to an alkene to yield an organoborane intermediate, RBH2. Oxidation of the organoborane by reaction with basic hydrogen peroxide, H2O2, then gives an alcohol
Hydration of alkenes (reaction names) Oxymercuration-demercuration and hydroboration (both add water and end with an OH)
Syn stereochemistry Two molecules add to the same face of an alkene's double bond
(catalytic) hydrogenation Alkenes react with H2 in the presence of a metal catalyst such as palladium or platinum to yield the corresponding saturated alkane addition products. (alkene + H2 + metal --> alkane)
Epoxide A cyclic ether with an oxygen atom in a three-membered ring.
Oxidation a reaction that results in a loss of electron density for carbon, caused either by bond formation between carbon and a more electronegative atom (oxygen, nitrogen, or a halogen) or by bond-breaking between carbon and a less electronegative atom (hydrogen)
Oxidation vs reduction Oxygen is added vs hydrogen is added
Preparation of alkenes Dehydration and dehydrohalogenation (alkane to alkene)
anti addition mechanism two substituents are added to opposite sides of a double bond or triple bond, once again resulting in a decrease in bond order and increase in number of substituents.
Syn resulting mechanisms Catalytic hydrogenation, hydroboration
Anti resulting mechanisms Addition of halogens, addition of hypohalous acids, oxy-demerc.
Electrophilic addition reaction Addition of HCl (CCl4), HBr (CCl4),or KI/H3PO4 (generating HI); regiospecific reaction b/c nucleophile adds to a specific region, following Markovnikov's rule.
Halohydrin A compound with a halogen and an OH on neighboring carbons (results from addition of hypohalous acid)
Hydration energy diagram 3 steps!
How to tell if an alkene product is major or minor... Find the most substituted alkene (mono is least, tetra is most)
Acid catalyzed addition of H2O (name solvents) H2O/H+ (H+ being any strong acid HCl, H3PO4, H2SO4, H3O+)
Addition of carbenes Cyclo addition reaction; forms a new ring. Reaction is concerted since bond breaking and bond forming happen at once
Carbene Carbon with one lone pair, connected to two R groups
Stereospecific reaction Can form only one specific isomer
Formation of trans 1,2 - diols Trans if mCPBA/CH2Cl2 is solvent followed by H3O+ as catalyst; the OH groups will be one dashed and one wedged.
Oxidative cleavage Double bond separation by a powerful oxidizing reagent, most commonly ozone (O3). Adding O3 with Zn/H+ to break a double bond into two compounds is called ozonolysis.
Ozonolysis (products?) 2-propene put in an O3 solvent with Zn/H+ will form an aldehyde and a formaldehyde
2-propene with kMnO4/H3O+ will form what products? Carboxylic acid and CO2
Stereochemistry of reactions Enantiomers are formed if "attack" from the top and bottom are equally likely (this occurs for flat carbocations). Diastereomers form if "attack" from top and bottom are NOT equally likely (this occurs when carbocation is not flat).
Formation of cis 1,2 - diols Cis if the solvents are OsO4/pyridine with NaHsO3/H2O, OR catalytic OsO4/acetone/H2O with NMO (Iess toxic), OR KMnO4/KOH/H2O
Alkene + 1. BH3/THF 2. H2O2/KOH --> Cis alkene with OH and H on either side (both wedge or both dash)
Alkene + 1. Hg(OAc)2 ,H2O 2. NaBH4 --> Alcohol attached to one side of where alkene was (oxymercuration)
OH containing molecule + 1. H2SO4 2. H2O --> Alkene forms where OH was and H2O is a byproduct
Alkene + 1. H2, 2. Pd/C --> Hydrogens on either end of where alkene was (cis)
Alkene + 1. mCPBA/CH2Cl2, 2. H3O+ --> trans-1,2- diol (OH on either side of where alkene was, one dash one wedge)
Alkene + 1. OsO4/Pyridine, 2. NaHSO3/H2O --> Alkene + 1. OsO4/acetone/H2O, 2. NMO --> Cis - 1,2 - diol (OH on either side of where alkene was) NMO is the less toxic method
Cycloalkene + 1. O3, 2. Zn, CH3CO2H --> cyclohexene breaks at double bond, one side become a ketone and the other side becomes an aldehyde
Cycloalkene + KMnO4 --> cyclohexene breaks at double bond, one side becomes a ketone and the other side becomes a carboxylic acid
Created by: 2024032091273279
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