Alkyl Halide Mechanism: E1 vs. E2 in Acidic and Basic Conditions

[predentalgirl1]

This is my question...
For the alkyl halide tell which mechanism, E1 or E2, will predominate under both stongly basic (with large base) conditions and strongly acidic. Tell if each reaction is expected to proceed relatively quickly, moderately, or slow (based on sterics for E2 and carbocation stability for E1). Finally, name the primary alkene produced in each case.




a.) 2-chloro-3-s-butylhexane

b.) 1-chloro-3-s-butylhexane

c.) 3-chloro-3-s-butylhexane


My answer...only part of part (a)...

acidic prefers E1, moderate rate, major product 3-s-butly-2-hexene. basic prefers E2.

How do I solve for the rest?? Someone please help me!

 

[predentalgirl1]

I'm sorry, I put this in the wrong forum and I do not know how to move it. This is a homework question.

 

[chemisttree]

I found this discussion on the Web:

Comparison or E1 and E2:
E2 vs E1:
E2 is characterized by:
· second order kinetics
· anti periplanar conformation for elimination
· absence of rearrangement
· reactivity sequence: CH3 < 1° < 2° < 3°

E1 is characterized by:
· first order kinetics
· rearrangement
· reactivity sequence: CH3 < 1° < 2° < 3°


For a given substrate, which mechanism will be followed? Whichever of these two processes goes faster determines which mechanism predominates.

To answer this question:

1. Consider the substrate (alkyl halide). It can either undergo deprotonation by a base leading to 1,2-elimination, or heterolysis to form a carbocation followed by deprotonation.
Reactivity by E2 increases mostly due to increasing stability of the alkene formed with a
more highly substituted alkyl group. Reactivity by E1 increases because of greater stability of the carbocation being formed in the rate determining step. Thus reactivity by both mechanisms increases as CH3 < 1° < 2° < 3°.

2. Consider the base. The rate of E2 depends on both the concentration and strength of the base, whereas E1 does not. In E1, the base must wait for the carbocation to be formed, so neither the concentration nor strength of the base will matter much. For a given substrate, the more concentrated or stronger the base, the more E2 will be favored over E1. Under the conditions usually used to bring about dehrydrohalogenation, strong and concentrated base, E2 usually occurs. In general the E1 mechanism is encountered only with secondary or tertiary substrates, and in solutions where the base is either in low concentration or weak, typically where the base is solvent.

http://depts.washington.edu/chemcrs/bulkdisk/chem237A_aut01/info_Ch_6&7.pdf

For acid-catalyzed eliimnation, the first step is the protonation of the halogen followed by elimination of the hydrogen halide. A carbocation is the result. (kinda like E1 in that respect)