Epoxides

[xjoey20x]

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Can someone explain which way the epoxide breaks?

I've been stuck on it for a while now.

Also, does the Nuc- attack the more substituted side or less substituted side?

 

[Seattle Mariners Fan]

It breaks and adds dependent on whether you're opening the epoxide with acid or a strong nucleophile.

In the case of using an acid to open it up, there's a carbocation intermediate and its an SN1 type reaction. A tertiary carbocation intermediate is more stable than a primary or secondary, so you see the nucleophile on the more substituated.

In the case of opening it with a strong nucleophile, this is an SN2 type reaction and there's never a carbocation. Since the binding of the nucleophile occurs before any other event, sterics are the most important factor.

http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch16reactionsepoxides.html

Map it out - diagram an epoxide and open it with an acid or with a nucleophile and the rest should make sense.

 

[xjoey20x]

It breaks and adds dependent on whether you're opening the epoxide with acid or a strong nucleophile.

In the case of using an acid to open it up, there's a carbocation intermediate and its an SN1 type reaction. A tertiary carbocation intermediate is more stable than a primary or secondary, so you see the nucleophile on the more substituated.

In the case of opening it with a strong nucleophile, this is an SN2 type reaction and there's never a carbocation. Since the binding of the nucleophile occurs before any other event, sterics are the most important factor.

http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch16reactionsepoxides.html


Map it out - diagram an epoxide and open it with an acid or with a nucleophile and the rest should make sense.

Thanks that helped to clear it up!