Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How would one judge whether a secondary carbon would react via SN1 or SN2? (Or both?)

  1. Dec 1, 2009 #1
    For example, if we have 2-butanol, a compound with a secondary [tex]\alpha[/tex] carbon and
    I reacted this with HCl and NH4Br

    I would get 2-bromobutane (via nucleophillic substitution), but how would I determine whether this goes via SN1 or SN2 to achieve this?

    Now, if this was 1-bromobutane, I know it would be via an SN2 reaction (steric hindrance)
    And if it was t-bromobutane, it would be via an SN1 reaction (carbocation)

    But since 2-bromobutane rests right in the middle, where do I find this balance? It would be a little bit of both the carbocation and steric hinderance involved, wouldn't it?

    My question:
    I've found some SN1/SN2 tables online (i.e. http://www.cem.msu.edu/~reusch/VirtualText/alhalrx3.htm#hal9) , which seem to point that 2-bromobutane should undergo SN2, because Br- is a weak base.


    But does that mean literally 100% of this entire reaction goes through SN2 then?
    Or is there a small ratio, like 95% SN2, and 5% SN1, but small enough to assume that SN2 is the entire reaction mechanism?

    Thanks for clearing this up.
     
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Dec 1, 2009 #2
    Re: How would one judge whether a secondary carbon would react via SN1 or SN2? (Or bo

    Consider what would happen here if you had, for instance (R)-butan-2-ol. What would be the product by SN1, or by SN2, and how do they differ?
     
  4. Dec 1, 2009 #3

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Re: How would one judge whether a secondary carbon would react via SN1 or SN2? (Or bo

    Protonating the alcohol makes it a wonderful leaving group. Excess acid converts the water into H3O+ and prevents it from adding back. Seems like you would get a little of SN1 and SN2. Maybe a couple of percent of the SN1 product. Solvent has an effect as well. How might a less polar solvent affect the outcome?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How would one judge whether a secondary carbon would react via SN1 or SN2? (Or both?)
  1. Sn1 vs Sn2 reactions (Replies: 2)

  2. Sn1 and sn2 reactions (Replies: 5)

Loading...