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Structure and reactivity are inseparably related.
Recall that we think about chemical reactions
on an energy diagram as proceeding from an energy well
- the starting materials,
over a peak - the transition state,
and finally down to another energy well - the products.
The structure and, more importantly, the stability
of all three of these structures
figures into reactivity in a very profound way.
More stable transition states, for instance,
often lead to faster reactions.
More stable products can lead to more exothermic reactions.
Because the stability and structure of intermediates
in transition states is so relevant to reactivity,
in this lesson we're going to take a look
at the factors that influence
the stability of reactive intermediates,
including charged species, which we've already seen,
as well as some new species that we haven't dealt with yet.
We'll also introduce the concept of bond order
and how we can use it to predict bond length,
strength, and reactivity.
Bond strength is one of the keys to molecular energy.
So comparing the total bond strength
of one molecule to another
gives us a good idea of their relative stabilities,
and, more importantly,
insight into the direction of equilibrium between the two.
As you progress through this lesson,
keep in mind that the end game is an understanding
of the factors that control the stability
of the reactive intermediates.
Understanding these factors
will give you insight into reactivity.
For instance, we can see on the diagram I've drawn here
that stabilization of the products
will lead to a larger energy gap
between the starting materials and products
and a more exothermic reaction.
This helps explain
the very large amount of heat, for instance,
that's released during a reaction
that's very thermodynamically favorable.
We can use considerations
of reactive intermediates and their stability
to explain these experimental observations.