[eureka123]

i am not getting same answers as given by book..
help plzz

[Arctic-Nation]

Please tell us how you've been tackling these questions first. What do you think happens (or doesn't happen)?

[eureka123]

in Q2 i think Br will attack double bond on ring to make it stable...

[Arctic-Nation]

For question 1, do you have any idea how acid might interact with double bonds?

The second problem is a bit above my level, and I'm not quite sure what will happen exactly. However, I'm quite sure HBr will not attack the cyclopropene double bond, but the other one. Check what kind of cation will be formed that way.

[eureka123]

i dont know what the term ""thermodynamic control "" implies ??

[sjb]

i dont know what the term ""thermodynamic control "" implies ??

Basically, the product that is thermodynamically favoured is the one with the lowest energy after reaction, rather than kinetic control, which is the product with the lowest activation energy. See, for instance, http://en.wikipedia.org/w/index.php?title=Thermodynamic_versus_kinetic_reaction_control&oldid=306626648 ?

[Arctic-Nation]

Thermodynamic and kinetic control are used to explain what product is formed when a reaction offers different reaction pathways.
Suppose a compound A, which can be converted into either product T (thermodynamic) or a product K (kinetic), and that all reactions are reversible. Product T is always more stable (has lower energy) than product K, but product K is formed faster (has a lower energy of activation). This means that if A is let allowed to react, both products T and K will be formed, but in the beginning of the reaction mainly product K will be formed (because this reaction goes faster).
Now, if you were to stop the reaction after only a short amount of time, product K will be the major product. We then say that the reaction happened under kinetic control (there was no time for the more stable product T to be formed). If, however, the reaction is allowed to run for longer times, then mostly product T will be formed. The reaction is then under thermodynamic control.

Usually, kinetic control means short reaction times and lower temperatures, while thermodynamic control means longer reaction times and higher temperatures (because the energy of activation is higher).

In your case, you should know what defines the stability of double bonds in terms of substituents, their position, and conjugation.

Also, thank you sjb.