166 CHAPTER 4 • INTRODUCTION TO ALKENES. …

166 CHAPTER 4 introduction to alkenes . structure AND REACTIVITY state of lower energy than the transition state for protonation to give a primary carbocation. Thestabilities of the carbocations themselvesdo not determine which reaction is faster; the relativefree energies of the transition states for carbocation formationdetermine the relative rates ofthe two processes. Only the validity of Hammond s postulate allows us to make the connectionbetween carbocation energy and transition-state n e e d H a m m o n d s p o s t u l a t e b e c a u s e t h e s t r u c t u r e s o f t r a n s i t i o n s t a t e s a r e u n c e r t a i n ,whereas the structures of reactants, products, and reactive intermediates are known. There-fore, knowing that a transition state resembles a particular species (for example, a carbocat-ion) helps us to make a good guess about the transition-state structure . In this text, we ll fre-quently analyze or predict reaction rates by considering the structures and stabilities ofreactive intermediates such as carbocations.

168 CHAPTER 4 • INTRODUCTION TO ALKENES. STRUCTURE AND REACTIVITY A large number of organic reactions are catalyzed. In this section, we’ll introduce the idea of catalysis by considering three examples of catalyzed alkene reactions.

Loading..

Tags:

  Introduction, Structure, Alkenes, Structure and, 4 introduction to alkenes, Catalyzed

Information

Related search queries