McMurry (Kap. 6,10) - Describing a reaction: intermediates

Question 1

What is an reaction intermediate?

Answer 1

The product which only exist transiently during the course of the multistep reaction.

As soon as it is formed, it reacts further with something else and forms another intermediate product (OR the final product).

EACH intermediate reaction has its own activation energy, transition state and energy change.

Question 2

A complete energy diagram contains the overall drawings of the individual reactants and products of the (starts reactants) + (intermediate reactants) + (final product).

The reaction intermediate lies at an energy minima between each step.

Each step in a multistep can always be considered separately (they have their own activation energy and energy change) - BUT the overall energy change is the difference between initial reactants and final product.

Answer 2

Yes.

Question 3

How does energy diagrams get drawn for biological reactions in living organisms?

Answer 3

Can be describes in similar way, however they are constrained by the fact that:

• They must have low enough activation energy to occur at moderate temperatures.
• They must release energy in relative small amounts to avoid overheating the organism.

These constraints are met through a structurally complex enzyme catalysts that change the mechanism of a reaction to an alternative pathway - proceeds through a series of small steps rather then one or two LARGE steps. The end result is the same, however.

See page 172 for examples of such energy diagrams.