CH 11 - Ethers, Epoxides, and Sulfides

the functional group of an ether is

an oxygen atom bonded to two carbon atoms (C-O-C)

in a normal ether, the oxygen atom is

sp3

if the oxygen in an ether is bonded to sp2 carbon, then the oxygen is

sp2

ether nomenclature - IUPAC parent chain

longest carbon chain is the parent

• name the OR group as substituent

ether nomenclature - common names

name the groups bonded to oxygen in alphabetical order followed by the word ether

ethoxyethane (CH3CH2OCH2CH3)

diethyl ether

although ethers are polar compounds, only forces that exist are

dipole-dipole attractive forces

boiling points of ethers are

• lower than alcohols of comparable MW

• close to those of hydrocarbons of comparable MWillw

Williamson ether synthesis

ether synthesis by the Sn2 displacement of halide, tosylate, or mesylate by an alkoxide ion

Williamson ether synthesis yields are highest with

methyl and primary halides

Williamson ether synthesis yield lower with

secondary halides (competing elimination)

Williamson ether synthesis reaction fails with

tertiary halides (elimination only)

acid-catalyzed dehydration of alcohols

poor LG (OH-) is converted to better one (H2O) to produce an ether

acid-catalyzed addition of alcohols to alkene

alkene to ether

acid-catalyzed addition of alcohol to alkenes - yields are highest using

an alkene that can form a carbocation and using methanol or primary alcohol that is not prone to undergo acid-catalyzed dehydration

ethers are cleaved by HX to

an alcohol and a haloalkane

a protect group must

• add easily to the sensitive group

• be resistant to the reagents used to transform the unprotected functional group(s)

• be removed easily to regenerate the original functional group

silly ethers protecting groups

TMSCl, TESCl, TBSMSCl, TIPSCl

what is used to remove silly ethers

Bu4N+F- salt

• source of F-

epoxide

a cyclic ether in which oxygen is one atom of three-membered ring

the most common lab method to create epoxide is

oxidation of an alkene using a peracid

epoxides are also synthesized using

halohydrins

• halohydrin followed by Williamson ether synthesis

sharpness epoxidation

stereospecific and enantioselective

ethers are not normally susceptible to

attack by nucleophiles

because of the strain associated with the three-meter ring, epoxides readily undergo a variety of

ring-opening reactions