Orgo Reaction Mechanisms

*NaBH4 Reduction of a Ketone

Reagents: H-, NaBH4
Mechanism: H- nucleophilically attacks carbonyl, NaBH4 goes to negative O
Product: Alcohol

*LiAlHa Reduction of a Ketone

Reagents: H-, LiAlH4
Mechanism: H- nucleophilically attacks carbonyl, LiAlH4 goes to negative O, stronger than NaBH4
Product: Alcohol

Chromic Acid Oxidation

Reagents: Cr2O7
Mechanism: Secondary alcohol to ketone
Product: Ketone, cannot make an aldehyde

PCC Oxidation

Reagents: PCC
Mechanism: Primary alcohol to aldehyde, secondary alcohol to ketone
Product: Aldehyde or ketone

Organolithium

Reagents: Li, CuBr
Mechanism: RBr addition of Li, CuBr addition
Product: R- or R2CuLi

Grignards

Reagents: Mg
Mechanism: Addition of Mg, create a good nucleophile
Product: RMgBr-

*Organolithium addition to carbonyl

Reagents: R2CuLi, H+
Mechanism: Nucleophilic attack at carbonyl, protonation of O- in second step
Product: Alcohol

*Grignard addition to carbonyl

Reagents: RMgBr
Mechanism: Nucleophilic attack at carbonyl, protonation of O- in second step
Product: Alcohol

*Synthesis of halide from alcohol

Reagents: Ms(Ts)Cl, SOCl2, PBr3
Mechanism: OH is LG, nucleophilic attack w halide
Product: RX

*Dehydration of alcohol

Reagents: H2O, H+
Mechanism: E1 elimination reaction or alcohol to alkene
Product: alkene

*Williamson ether synthesis

Reagents: NaH (strong base), CH3X
Mechanism: Deprotonation of alcohol, substitutes w/ RX
Product: ether, can product asymmetric ether

*Acidic opening of epoxide

Reagents: H+, ROH
Mechanism: carbocation attack from bottom at more substituted carbon
Product: Formation of alcohol with O from epoxide at less substituted

*Basic opening of epoxide

Reagents: -OR”
Mechanism: attack at less substituted carbon (Sn2)
Product: Formation of alcohol with O from epoxide at more substituted

*Acidic cleavage of ether

Reagents: H+, H2O
Mechanism: Substitution reaction at ether
Product: ROH + R’OH

Catalytic hydrogenation

Reagents: H2, Pd/C or Pt
Mechanism: Syn addition across double bond at metal surface
Product: cis hydrogen substituents

*Dehydration of alcohol

Reagents: H2O, N2SO4
Mechanism: Protonation of alcohol, then E1, must be acidic
Product: Alkene

*HX Addition

Reagents: HCl or HBr
Mechanism: Addition of H to form carbocation, X- adds to more substituted
Product: X addition to more substituted side of double bond

*Hydration of alkene

Reagents: H2O
Mechanism: Addition of H+ to form carbocation, H2O nucleophilically attacks at more substituted
Product: Alcohol

*X2 Addition

Reagents: X2
Mechanism: halonium forms, anti addition of X-
Product: trans halogen substituents across double bond

*Haloalcohol synthesis

Reagents: X2, H2O
Mechanism: halonioum ion forms, H2O acts as nucleophile, anti addition OH- at more substituted
Product: haloalcohol with OH at more substituted

Epoxide formation with peracid

Reagents: mCPBA
Mechanism: single step (concerted) addition across double bond
Product: epoxide (syn addition)

Oxymecuration/reduction

Reagents: 1. Hg(OAc)2, OH-, 2. NaBH4
Mechanism: formation of mercurium ion, anti addition of OH- at more substituted, reduction/removal of mercury ion
Product: Markovnikov alcohol at more substituted carbon

Hydroboration/oxidation

Reagents: 1. BH3, 2. H2O2, NaOH
Mechanism: initial syn addition across double bond, oxidation and nucleophilic attack w/ OH-
Product: anti-Markovnikov alcohol at least substituted carbon

Ozonolysis

Reagents: O3
Mechanism: free radical
Product: two ketone, cleavage at double bond

Syn dihydroxylation with OsO4

Reagents: OsO4, baste H2O
Mechanism: Syn addition of OH on both sides of double bond
Product: cis OH substituents

Weakly basic and neutral nucleophile (H2O, ROH), tertiary RX

Sn1 or E1

Weakly basic and neutral nucleophile (H2O, ROH), secondary RX

Sn1 or E1

Weakly basic and neutral nucleophile (H2O, ROH), primary RX

No reaction

Weakly basic and neutral nucleophile (H2O, ROH), Me RX

No reaction

Moderately nucleophilic, weakly basic (Cl-, Br-, CN-), tertiary RX

No Reaction, good nucleophile favors Sn2 but cannot occur at tertiary carbon

Moderately nucleophilic, weakly basic (Cl-, Br-, CN-), secondary RX

Sn2

Moderately nucleophilic, weakly basic (Cl-, Br-, CN-), primary RX

Sn2

Moderately nucleophilic, weakly basic (Cl-, Br-, CN-), Me RX

Sn2

Basic, charged, small nucleophile (OH-, MeO-, EtO-), tertiary RX

E2

Basic, charged, small nucleophile (OH-, MeO-, EtO-), secondary RX

Sn2 or E2

Basic, charged, small nucleophile (OH-, MeO-, EtO-), primary RX

Sn2 or E2, Sn2 favored without heat

Basic, charged, small nucleophile (OH-, MeO-, EtO-), Me RX

Sn2

Basic, charged, bulky nucleophile (KOt-Bu), tertiary RX

E2

Basic, charged, bulky nucleophile (KOt-Bu), secondary RX

E2

Basic, charged, bulky nucleophile (KOt-Bu), primary RX

E2

Basic, charged, bulky nucleophile (KOt-Bu), Me RX

No reaction

*Sn1

Mechanism: leaving group leaves and substituted for nucleophile, two step through carbocation
Product: R-Nu
Notes: Stereochemistry lost at the reaction site, tertiary carbocation is best

*Sn2

Mechanism: leaving group leaves and substituted for nucleophile, one step
Product: R-Nu
Notes: Inversion of stereochemistry, sensitive to steric bulk

*E1

Mechanism: leaving group leaves, goes through carbocation, beta hydrogen abstracted
Product: alkene
Notes: tertiary carbocation is best, neutral base

*E2

Mechanism: leaving group leaves and beta hydrogen is abstracted, one step (concerted)
Product: alkene
Notes: needs a strong base