1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Nucleophilic substitution question!

  1. Mar 12, 2008 #1
    1. The problem statement, all variables and given/known data

    I have these compounds, and I have to predict which one will undergo unimolecular substitution reaction the fastest. And which one will undergo it the slowest.

    3 bromo cyclohexene
    1 bromo cyclohexene
    4 bromo cyclohexene
    2 bromo hexane (not cyclohexane/ene)
    The solvent is a combination of Ethanol and Silver Nitrate.

    So I'm definately sure this reaction will proceed SN1. I am also unsure of this: what causes the leaving group to leave in a SN1 reaction? . I know a good leaving group is stable because it's large. And in SN2 a leaving group 'leaves' because you have a backside attack by a nucleophile.

    2. Relevant equations


    3. The attempt at a solution

    Fastest: I'm guessing 2 bromo hexane will react the fastest, because when you get it's carbocation, the carbon bearing that cation is 2* substituted.

    The rest: I'm not sure about the others. You get a cycloalkene carbocation in each one. But they all have six carbons. They all seem to be 2* substitued.
  2. jcsd
  3. Mar 13, 2008 #2
    Don't forget resonance, which can confer additional stability to carbocations. This effect is often stronger than that of substitution.
  4. Mar 13, 2008 #3
    It is an Sn1 reaction, and one that is frequently used in labs. Leaving groups are usually substituents on a molecule that benefit less from being a substituent than just taking the electrons from the bond and becoming independent. For example, -OH is a bad leaving group because if it detaches from the molecule, it takes the electrons from the bond to create a hydroxide ion, which is very unstable (quick to react with something), so it would rather stay put. -OH2+, on the other hand, is a good leaving group because it will become H20, which is much more stable.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook