[sharbeldam]

Now it is known that e2 can happen if the alkyl halide was primary secondary or tertiary but the question is that how we do know which goes faster? Do we predict the products, and the more sub Alkene will tell us that the initial reactant undergo it faster? As if the e2 can see its future product?
And can you explain the answer to the first problem?

Thanksss

[rolnor]

If the reaction is faster, does this mean that the neccesary energy of activation is lower? If the double bond becomes part of a conjugated system, does this compound have a lower energy-state than a non-conjugated system? Can a very thermodynamicaly favoured reaction still be very slow?

[Babcock_Hall]

What have you learned about the degree of substitution of the bromoalkane and the rate of reaction?  Additional factors can come into play, as Rolnor has suggested.  Can you make an attempt to answer these questions now?

[sharbeldam]

Ok let's see.
So the first one is right since it is a conjugated alkene.

the second one is still confusing, the carbon on the right is tertiary and the one on the left is secondary, now this is confusing, since in this reaction we don't get carbocation, we look at the more sub alkene, but both of them can lead to 3 subs on the alkene, unless the one on the right forms a double bond through between the chain and the cyclohexane and we consider the cyclohexane two subs.

third one;s answer is the molecule on the right since it will give us more sub alkene.

forth one is the molecule on the right since it also gives us more sub alkene.

5th one is also same reason.

so basically only the second one remains confusing.

[Babcock_Hall]

I think that there are two concepts that are not entirely unrelated but are separable.  The second example can be explained on the principle that the rate of E2 reactions increases with an increasing degree of substitution.

[sharbeldam]

Oh you mean that because there is bromine and the cyclohexane on the SAME carbon so it makes that carbon with 4 substituents? not the most sub alkene in the end.
And if there is a cyclohexane connected via a double bond to the chain, do you consider the cyclohexane 1 sub or two?
since there is two bonds coming out of the double bond but still its a cycle.

[Babcock_Hall]

I don't count the non-carbon groups.  One substrate is tertiary, and the other one is secondary.  I am not certain of the answer to your other question.

[sharbeldam]

Thank you, i appreciate the help