The epoxide ring is opened by both bases and acids in different ways.
When an acid is used, the electrons from the oxygen seek a proton from the
acid, and protonate the epoxide. The protonated epoxide is now able to
react with a weak nuclophile (nucleophile attacks to backside of carbon),
and opens the ring. The molecule now consists of an alcohol one one side,
and a protonated glycol (or -OHR). The hydrogen of the protonated alcohol
is removed by the conjugate base of the acid, leaving you with eitheir a
glycol, or an ether with an acohol.
When a base is used to open the ring, the base (RO- strong nucleophile)
attack
the carbon baring the ring from the backside. The forms an alkoxide ion
(ether with an O- on opposite side). The alkoxide ion is very basic and
abstracts a proton from the base's conj. acid. The finished reaction now
has an ether addition on one end and an alcohol on the other.
Read page 450 for more info!
Scott
PS basecatalyzed ring openings attack at less substituted carbon atom.
acidcatalyzed ring openings, nucleophile attacks at more substituted
carbon atom.
On Fri, 13 Dec 1996 moehrikm@plu.edu wrote:
> hey chem people!
> i hope everyone's studying is going well. perhaps someone could
> take the time to explain the epoxide ring opening in both acids and bases.
> i think i understand the general princial but i would like to be better
> acquainted with the mechanisms. thanks again and good luck on finals!
> kate
>
>