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Topic: SN2 Reaction question  (Read 3433 times)

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Offline G O D I V A

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SN2 Reaction question
« on: November 15, 2009, 02:11:39 AM »
What would be the stereostructure of the product obtained when (R)-2-bromo-propionitrile () undergoes SN2 reaction with
ethanethiolate (Na+ -SCH2CH3); in ethanol.

I dont know which would be the nucleophile and which would be the leaving group.  The question goes on to ask what the configuration (R/S) is on the product so it must be either the cyanide or the bromine leaving and the -SCH2CH3 adding?  Is that right?

Offline Dan

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Re: SN2 Reaction question
« Reply #1 on: November 15, 2009, 08:54:37 AM »
it must be either the cyanide or the bromine leaving and the -SCH2CH3 adding?  Is that right?

Yes. So which is the better leaving group - bromide or cyanide?
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Offline pantsboy

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Re: SN2 Reaction question
« Reply #2 on: December 04, 2009, 10:50:12 PM »
good Leaving Groups are typically weak bases which are conjugates of strong acids.  HBr is a strong acid with a pKa of -9 and HCN is weak with a pKa of 9.21.  In general, if the pKa of a conjugate acid is higher than 2 it will not function as a leaving group.

Offline Scatter

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Re: SN2 Reaction question
« Reply #3 on: December 05, 2009, 01:15:57 PM »
See ya later, Br!

Seriously, Br just likes to get up and walk out all the time.  Another molecule starts getting frisky with its carbon's nucleus and it just backs off.  A "weak" base for sure.

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