Yes, this is an E2-type of elimination. The reactive conformation is that in which the two C-Br bonds are mutually trans, which sets them up for concerted elimination of Br2 via an anti, coplanar transition state. Iodide ion functions as a nucleophile to attack one of the bromine atoms, which at the time of reaction is polarized toward Br(delta+) [positive halogen, electrophilic; the leaving group is polarized toward Br(delta -)]. The dehalogenation reaction proceeds through a transition state analogous to that associated with concerted anti, coplanar E2 elimination. The products are the corresponding alkene, IBr [polarization I(delta +) Br(delta -)]and bromide ion.
For additional information see Goering, H. L.; Espy, H. H. J. Amer. Chem. Soc. 1955, 77. 5023-5026.
Yes, this is an E2-type of elimination. The reactive conformation is that in which the two C-Br bonds are mutually trans, which sets them up for concerted elimination of Br2 via an anti, coplanar transition state. Iodide ion functions as a nucleophile to attack one of the bromine atoms, which at the time of reaction is polarized toward Br(delta+) [positive halogen, electrophilic; the leaving group is polarized toward Br(delta -)]. The dehalogenation reaction proceeds through a transition state analogous to that associated with concerted anti, coplanar E2 elimination. The products are the corresponding alkene, IBr [polarization I(delta +) Br(delta -)]and bromide ion.
For additional information see Goering, H. L.; Espy, H. H. J. Amer. Chem. Soc. 1955, 77. 5023-5026.
You need to look carefully at the electron movements in the mechanism and less attention to the term "E2 elimination". We often use E2-elimination to refer to a dehydrohalogenation. This is a different reaction. In this case iodide is an electron donor. The product will also contain an I3- ion. You would get the similar reaction if you did a reductive elimination with a dissolving metal.
You need to look carefully at the electron movements in the mechanism and less attention to the term "E2 elimination". We often use E2-elimination to refer to a dehydrohalogenation. This is a different reaction. In this case iodide is an electron donor. The product will also contain an I3- ion. You would get the similar reaction if you did a reductive elimination with a dissolving metal.
Thanks for the *delete me* Now, the question asked for the major product. Iodide is a good nuleophile and weak base, and from what I've read this should favour Sn2 over E2. Why is the E2 product the major one?
Thanks for the *delete me* Now, the question asked for the major product. Iodide is a good nuleophile and weak base, and from what I've read this should favour Sn2 over E2. Why is the E2 product the major one?
For additional information see Goering, H. L.; Espy, H. H. J. Amer. Chem. Soc. 1955, 77. 5023-5026.
Hope this helps.
For additional information see Goering, H. L.; Espy, H. H. J. Amer. Chem. Soc. 1955, 77. 5023-5026.
Hope this helps.
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