Advices For Studying Organic Chemistry

isomers when hydrogenation converts them to the same product.

• H 2 Pt CH 3 CH 2 CH 2 CH (^3) ∆Ho = −127 kJ mol-1
  1-Butene (C 4 H 8 ) Butane
  CH 3 CH 2 CH CH 2


• H 2 Pt CH 3 CH 2 CH 2 CH 3 ∆Ho^ = −120 kJ mol-1
  Butane
  CC
  H
  H 3 C CH 3
  H
  cis-2-Butene (C 4 H 8 )


• H 2 Pt CH 3 CH 2 CH 2 CH 3 ∆Ho^ = −115 kJ mol-1
  Butane
  CC
  CH 3
  H 3 C
  H
  H
  trans-2-Butene (C 4 H 8 )

2. In each reaction:
   
   
   1. The product (butane) is the same.
   
   
   2. One of the reactants (hydrogen) is the same.
   
   
   3. The different amount of heat evolved is related to different stabilities (different
      heat contents) of the individual butenes.
   
   
   
   

Figure 7.1 An energy diagram for the three butene isomers. The order of
stability is trans-2-butene > cis-2-butene > 1-butene.