Explain E2 reaction of alkyl halides?

Question

Please don't give me mechanism cause i can't understand it...

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Answer 1

I hope this helps

Alkyl Halide Reactions

The functional group of alkyl halides is a carbon-halogen bond, the common halogens being fluorine, chlorine, bromine and iodine. With the exception of iodine, these halogens have electronegativities significantly greater than carbon. Consequently, this functional group is polarized so that the carbon is electrophilic and the halogen is nucleophilic, as shown in the drawing on the right.  Two characteristics other than electronegativity also have an important influence on the chemical behavior of these compounds. The first of these is covalent bond strength. The strongest of the carbon-halogen covalent bonds is that to fluorine. Remarkably, this is the strongest common single bond to carbon, being roughly 30 kcal/mole stronger than a carbon-carbon bond and about 15 kcal/mole stronger than a carbon-hydrogen bond. Because of this, alkyl fluorides and fluorocarbons in general are chemically and thermodynamically quite stable, and do not share any of the reactivity patterns shown by the other alkyl halides. The carbon-chlorine covalent bond is slightly weaker than a carbon-carbon bond, and the bonds to the other halogens are weaker still, the bond to iodine being about 33% weaker. The second factor to be considered is the relative stability of the corresponding halide anions, which is likely the form in which these electronegative atoms will be replaced. This stability may be estimated from the relative acidities of the H-X acids, assuming that the strongest acid releases the most stable conjugate base (halide anion). With the exception of HF (pKa = 3.2), all the hydrohalic acids are very strong, small differences being in the direction HCl < HBr < HI.

http://www.cem.msu.edu/~reusch/VirtualTe...

Answer 2

Ingold, back in the 1920's or 30's, proposed a model to explain a peculiar type of chemical reaction: the E2 mechanism. E2 stands for bimolecular elimination and it has the following specificities...

a) It is a one-step process of elimination with a single transition state.

b) Typical of secondary or tertiary substituted alkyl halides. It is also observable with primary alkyl halides if a hindered base is used.

c) The reaction rate, influenced by both the alkyl halide and the base, is second order.

d) Because E2 mechanism results in formation of a Pi bond, the two leaving groups (often a hydrogen and a halogen) need to be coplanar. An antiperiplanar transition state has staggered conformation with lower energy and a synperiplanar transition state is in eclipsed conformation with higher energy. The reaction mechanism involving staggered conformation is more favourable for E2 reactions.

e) Reaction often present with strong base.

f) In order for the pi bond to be created, the hybridization of carbons need to be lowered from sp3 to sp2.

g) The C-H bond is weakened in the rate determining step and therefore the deuterium isotope effect is larger than 1.

h) This reaction type has similarities with the SN2 reaction mechanism.

The reaction fundamental elements are a) reaking of the carbon-hydrogen and carbon-halogen bonds in one step and, b) formation of a C=C Pi bond...

Hope this helps!!!