A Guidebook to Mechanism in Organic Chemistry

Nucleophilic Substitution at a Saturated Carbon Atom

(vi) The formation of alkyl halides:

R-OH+H® -»• R-OH

H

BrQ + R-OH -*• BrR + HaO

H

(vii) The cleavage of ethers:

Ph OR+H® ->PhOR •

PhOR + I® PhOH+RI

H

(viii) The formation of esters:

R' • CO,® + RBr -*• R'-C0 2 R + Br©

(ix) The formation of ethers:

RO©+R'Br -fR'OR'+Br^9

m

(x) LiAIH 4 reduction of halides:

LfAlH.+RBr -* LiAlH 3 Br+HR

Here the complex hydride is, essentially, acting as a carrier for hydride

ion, H®, which is the effective nucleophile.

(xi) Ring fission in epoxides:

Cl^CHj—CH 2 -> ClCHjCHjO^9

C1CH 2 CH, Oe+H 2 0 C1CH, CH 2 OH+eOH

Here it is the relief of strain achieved on opening the three-membered
ring that is responsible for the ready attack by a weak* nucleophile.
This is only a very small selection: there are many more displace­
ment reactions of preparative utility and synthetic importance.