Question

Select all the correct statements, there is more than one.

a. Experiments to determine mechanisms involve looking at indirect evidence to help support or disprove a proposed mechanism.
b. Most intermediates are not typically isolated to determine reaction mechanisms.
c. Transition states can be isolated and characterized to determine reaction mechanisms.
d. Carbocations are very reactive and are typically not isolated for analysis.
e. Carbocations can be routinely isolated (separated from a reaction mixture) and analyzed.
f. Scientists can prove that a specific mechanism exists.
g. Evidence of intermediates sometimes can be seen using techniques such as nuclear magnetic resonance spectroscopy.

Answer 1

Correct statements regarding chemical reaction mechanisms are that they use indirect evidence to support hypotheses (a), intermediates are not typically isolated (b), transition states can't be isolated (c is incorrect), carbocations are reactive and not isolated (d), and NMR can provide evidence of intermediates (g). The wrong concepts are the isolation of carbocations (e) and the proof of mechanisms (f).

Step-by-step explanation:

In chemical reaction mechanisms, we often rely on indirect evidence to confirm the steps involved because direct observation is not always possible. Therefore, statement (a) is correct, as experiments do involve examining indirect evidence to support or disprove proposed mechanisms.

Most intermediates, such as carbocations, are highly reactive and tend not to be isolated during these experiments, making statement (b) correct and (e) incorrect. Additionally, as mentioned in statement (d), carbocations are generally too reactive to be isolated for analysis. Statement (c) is incorrect because transition states, which are high-energy configurations that occur during chemical reactions, cannot be isolated since they are ephemeral and exist only at the moment of conversion from reactants to products or intermediates.

Scientifically, we cannot prove that a mechanism is definitive, but rather we can gather evidence that supports its plausibility. Hence, statement (f) is incorrect. Statement (g) is correct, as spectroscopic techniques like nuclear magnetic resonance (NMR) spectroscopy can often provide evidence for the existence of reaction intermediates.

Answer 2

Experiments to determine mechanisms involve looking at indirect evidence to help support or disprove a proposed mechanism.

Most intermediates are not typically isolated to determine reaction mechanisms.

Carbocations are very reactive and are typically not isolated for analysis.

Scientists can prove that a specific mechanism exists.

Evidence of intermediates sometimes can be seen using techniques such as nuclear magnetic resonance spectroscopy

Step-by-step explanation:

The study of reaction mechanism and chemical kinetics often form the main thrust of study in organic, inorganic and physical chemistry.

We often want to know the actual processes involved in the conversion of one specie to another. Unfortunately, this information may have to be obtained indirectly by certain chemical reactions or by the use of new instrumental methods such as nuclear magnetic resonance spectroscopy.

Many organic reactions have carbocation intermediates. These carbocations are relatively short-lived and are transient intermediates which are rarely isolated unless they are isolated in a molecular cage using a macromolecule or in superacids.

By intensive study, scientists can proof or disprove the authenticity of any proposed mechanism.

We must know that a transition state has partial bonds. It is often an extremely short-lived specie which cannot be isolated.