rxn rules

Dehydration of alcohols under strongly acidic conditions

Sn1 only with carbocation intermediate 

H-Cl, H-Br, H-I as nucleophile/bases attacking an alcohol

Step 1: protonation of alcohol, generating our nucleophile as well

Step 2: leaving group leaves, generation of carbocation

Step 3: Consider any possible carbocation rearrangement

Step 4: Substitution (Sn1) via attacking LUMO p-orbitals with Br, Cl, or I minus

Substitution of 1° and 2° alcohols with halides under conditions that do not allow carbocation rearrangement

Substitution of 1° and 2° alcohols with halides under conditions that do not allow carbocation rearrangement

Sn2

Opening of epoxides with strong nucleophiles (-OH, -OR, -CN, -N3, -SR, NH3)

Opening of epoxides with H-Z (Z = Cl, Br, I, H2O, ROH)

Dehydration of alcohols with POCl3 / pyridine

Conversion of alcohols into alkyl tosylates (tosylate is a good L.G.; more or less equivalent to a halide)

H-X

H on less substituted, +on more substituted, followed by attack by halide from both sides

Syn and anti

syn + anti

H2SO4, H2O

H on less subbed, +on more subbed

H2O attacks CI, deprotonated

Stereospecificity: none, attack either side

Syn and anti

SN2 only

PBr3, SOCl2,

Epoxide w/ strong nucleophile

E1 only with carbocation intermediate

TsOH, H2SO4

Step 1: protonation of alcohol

Step 2: leaving group leaves, generation of carbocation

Step 3: Consider any possible carbocation rearrangement

Step 4: Elimination (E1) via attacking beta protons

E2 only, no carbocationic intermediate

POCl3