ochem 1 mechanism overviews

Nucleophilic attack

Nucleophile attacks electrophile (lone pair or pi bond)

Loss of a Leaving Group

Heterolytic bond cleavage, results in a C^+

Proton Transfer

Protonation or Depeotonation (transfer of a H

Carbocation Rearrangement

Carbo cations will move to form more stable carbo cations (3° most stable)

Substitution Reaction

Loss of a leaving group AND Nucleophilic attack

Sn2

Concerted

Backside nucleophilic attack

Inversion of a chiral center

Requires a strong nucleophile

Backside attack

e^- density is too great on the front side, repels from the front

Sn1

Step-wise

Loss of a Leaving group 1st (RDS)

Products are a mix of R/S

Does not require a strong nucleophile

Elimination Reaction

Requires a Beta-H and base

Product is an alkene

E2

Concerted

Iodine is the best LG

3° is the fastest

Major/minor depends on base

E1

Step-wise

Carbocation intermediate

3° fastest

Favored by weak bases

Major = Zaitsev

Akyl halide w/ CH3O2Na produces a(n)

Ester

Preparation of internal alkynes

Requires a dihalide reagent

E1/E2

Need a base in excess

Solvent(s) required for make a terminal alkyne

xs NaNH2 or NH3

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H2O

Hydrogalogenation

Addition of an H and X across a pi bond

Markovnikov addition

Hydrohalogenation with a peroxide (ROOR, H202)

Anti-Markovnikov

Acid-catalyzed hydration

Addition of H and OH across a pi bond

Markovnikov (OH to more sub C)

Requires H3O+, H2SO4, H+ from H2O

Hydration of alkynes

H2O, H2SO4

Produces ketones

Terminal requires heat

Oxymercuration-demercuration

Solvent(s): Hg(OAc)2, H2O, NaBH4

Markovnikov and Anti-Markovnikov addition of H and OH

Requires a alkene reagent

Hydroboration-oxidation

Solvents: BH3•THF, NaOH, H2O2

Anti-Markovnikov addition of H and OH after BH3 addition

Requires a alkene reagent

Hydroboration-Oxidation (alkynes)

Selective of anti-Markovnikov

Enol and keto formation

BH3 for 2 successive additions

R2BH to stop the 2nd addition (9-BBN) (bulky)

Catalytic Hydrogenation (alkene)

The addition of H2 across a C=C

Syn addition

Solvents: H2 (hydro), Metal(Pt,Pd/c etc.)(catalyst)

Catalytic Hydrogenation (alkyne)

Two equivalent H2 required for alkane conversion

Stops at alkene from a poisoned catalyst (i.e. Lindlar’s)

Dissolving Metal Reduction

Reduces an alkyne to a trans alkene with Na and NH3

Trans product only

Can be reduced to an alkane w catalytic hydrogenation

Anti Dihydroxylation

Anti addition of OH and OH across a pi bond Markovnikov

mcPBA, H3O+

Halogenation: anti

Two halogen atom addition across pi bond Markovnikov

Solvents: Cl2, Br2

Halogenation (alkynes)

Yields tetrahalide

Requires xs Cl2, Br2 + CCl4

Hydrohydrin

Halogenation in H2O or other nucleophilic solvent

Br2, H2O(/alcohols, amines, thiols)

OH and Br addition (OH more substituted)

Syn Dihydroxylation

Adds OH and OH across pi bond

Somvents: OsO4 and NMO/C4H9OOH

Ozonolysis

Ozone cleaves an internal pi bond into a ketone and aldehyde

Terminal into CO2 and carboxylic acid