Energy diagram reactions

Step through the sequence of structures corresponding to combination of two methyl radicals to give ethane (methyl radical combination). 

Plot energy (vertical axis) vs. carbon-carbon distance (horizontal axis). Is this reaction endothermic or exothermic Is there a point on the diagram that can be identified as a transition state If so, what is the barrier for this reaction  

Plot energy (vertical axis) vs. CiC bond distance (horizontal axis), and repeat the analysis described above. 

Both of the reactions, radical combination and Diels-Alder cycloaddition, cause new bonds to be made. Bond making normally releases energy. Why then are the barriers for the two reactions so different (Hint Consider the nel bond making/bond breaking in the two reactions.) 

---

Select Energy (Properties menu). Notice that it updates automatically as you go from one frame to another. This allows you to easily construct reaction energy diagrams (energy vs. frame number or vs. a specific geometrical parameter). Make such a plot for this Sn2 reaction. Note, that the reaction as written is thermodynamically favorable, i.e., it is exothermic. Note also, that only a relatively small energy barrier needs to be surmounted. 

For each reaction, plot energy (vertical axis) vs. the number of the structure in the overall sequence (horizontal axis). Do reactions that share the same mechanistic label also share similar reaction energy diagrams How many barriers separate the reactants and products in an Sn2 reaction In an SnI reaction Based on your observations, draw a step-by-step mechanism for each reaction using curved arrows () to show electron movements. The drawing for each step should show the reactants and products for that step and curved arrows needed for that step only. Do not draw transition states, and do not combine arrows for different steps. 

The Hammond Postulate implies that the transition stah of a fast exothermic reaction resembles the reactants (se( reaction energy diagram at left). This means that it wil be hard to predict the selectivity of competing exothermi( reactions both barriers may be small and similar even i one reaction is more exothermic than the other. 

Use of the Hammond Postulate requires that the reverse reactions both be fast. Obtain energies for the transition states leading to 1-propyl and 2-propyl radicals ipropane+Br end and propane+Br center), and draw a reaction energy diagram for each (place the diagrams on the same axes). Is use of the Hammond Postulate justified Compare the partial CH and HBr bond distances in each transition state to the corresponding distances in propane and hydrogen bromide, respectively. Does the Hammond Postulate correctly predict which bond distances will be most similar Explain. 

Describing a Reaction Energy Diagrams and Transition States 157... 

Reaction energy diagram. During the reaction initiation, 134 kj—the activation energy Fa— must be furnished to the reactants for every mole of CO that raacts. This energy activates each CO—N02 complex to the point at which reaction can occur. 

Draw a reaction-energy diagram for the reaction if its activation energy is 37 kj. 

Figure 1.17 Reaction energy diagram of NH3 activation compared on different surfaces (energies in kilojoules per mole).

Figure 1.18 Reaction energy diagram that compares direct NH3 activation and NH3 (-) activation through reaction...

Fig. 14. Reaction energy diagram for the formation of DME from methanol, proceeding by an associative path without intermediate methoxy formation. Energies are in kj/mol ads refers to an adsorbed complex, ts to a transition state. Reprinted with permission from Ref. 244. Copyright 1996 American Chemical Society.

Given information about the energetics of a reaction, be able to construct an appropriate reaction energy diagram. 

A reaction energy diagram that fits the requirements stated in the problem is shown below. Notice that the diagram is a composite of the two diagrams drawn for Problems 3.17 and 3.16, in that order. 

The reaction takes place via an Sn1 mechanism because the substrate is a tertiary halide. The expected product is tert-butyl methyl ether. The reaction energy diagram resembles that for the SN1 reaction shown in Figure 6.2 ... 

For highly reactive aromatics, an additional kinetic step with the formation of a first intermediate (re-complex) between Steps (ii) and (iii), must be considered in the above mechanism (Scheme 5.2). Reaction energy diagrams show that in activated aromatics, the reactivity is controlled by the transition state with the highest activation barrier (re-transition estate), while the position selectivity depends on... 

Reaction energy diagrams for an electrophilic addition to an alkene and ( ) an electrophilic... 

Q Draw a reaction-energy diagram, and use it to identify the factors controlling the thermodynamics and kinetics of a reaction. 

---