Pericyclic Reactions and the Woodward Hoffman Rules - Assignment Example

Pericyclic Reactions and the Hoodward Hoffman Rules Name Professor Institution Course Date 1. Suggest mechanisms for the three reactions below. The mechanism that is involved in the reaction is thermally sigmatropic reaction. The high temperature breaks the existing bonds within the molecules thereby leaving molecules free and nitrogen molecule escaping to the atmosphere. The remaining molecules rearranged sigmatropically forming new compound. Nitrogen triple bond is broken due to the high thermal energy subjected to the substances thereby segregating into its constituent’s atoms. The mechanism that is involved the reaction is cycoaddition reaction that contains conjugated pi system containing four pi electrons. There is the addition of two distinctive pi bond containing varies components. The components eventually linked by the newly formed dual pi bond at the end and then resurface. The reaction that takes during cycoaddition process is exothermic reaction it normally being favor by the relative low temperature. Cycoaddition reaction takes place at the intermediate temperature that is mainly used to overcome the activation energy. This process results to the formation of the cyclic products that may take the form of either intermolecular or intramolecular structure. This reaction entails the mechanism of the photochemical process. There is the conservation of the C axis which is mainly aided through the means of conrotatory. This mode conrotatory takes place in a specified way thereby resulting to the formation of the new structures. The mode of the ring closure is suprafacial. The HOMO electrons is excited by the photo light are in antisymmetric because the MOs of the linear conjugated pi bonds systems which contain the number which normally alternate in a symmetry manner starting with the lowest energy commencing with the MO taking the form symmetric. However, the form of the rotation is not depicted within the thermal cyclization. 2. What is going on in the two reactions below? Draw the MO diagrams for the reactions and explain why the reaction on the right occurs at a lower temperature than the reaction on the left. In the first diagram, there is the formation of the new product that is formed through high temperature. It is taking place through the process of thermal breakage and rearrangement of the atoms and the molecules that eventually leads to the formation of new strong substance. This process is called sigmatropic symmetry rearrangement of molecules. The high thermal temperature breaks the covalent bonds that coexist amidst the molecules of the initial reactant and then realigning the molecules to form the new strong product. The formation of the first product results from the photochemical forbidden e- DIS reaction, hence, makes it faster as compared to the reaction on the right hand side .This reaction is thermally allowed. The second diagram involves the thermal cycoaddition process that entails the breaking of the existing bonds amidst the structures at relatively lower temperature and then realigning them to form new products. However, it takes place at a lower pace and at a lower temperature as compared to the first process. This is mainly because the second reaction process entails the formation of the product through the photochemical allowed way in combination to the thermal energy. All this takes place through e- DIS reaction manner, thereby making it to be at relatively lower rate as compared to the first process. This reaction is photochemically allowed. The process on the left side requires high temperature of the operation to act as the activation energy that will initially ignites and start the reaction. This is due to the fact that the reaction is not favored by the photochemical energy. Conversely, the reaction on the right side requires relatively lower temperature for its operation since it is favored by the photochemical energy that fuel the process in the initial stages. Hence, it does not require activation energy to commence reaction. 3. Suggest a mechanism for the reaction below. This reaction has been reported to go 105 times more rapidly in CF3COOH than in a non‐polar solvent – suggest why in terms of your mechanism. The mechanism taking course in the reaction above is sigmatropic shift. This mechanism entails breaking up of the existing hydrogen bonds and allowing the attachment of other atoms. The present bonds were broken thereby giving room for attachment of extra hydrogen to pair with oxygen molecule within the existing structure. The reaction requires the antarafacial hydrogen movement. This allows proper arrangement of the hydrogen atoms. Moreover, this arrangement allows sp3 hybrid lobe of C-H carbon to overlap with the nearest adjacent pz thereby making the hydrogen atom to face the opposite end of the structural face. Sigmatropic reaction takes place relatively at a faster rate in the CF3COOH as compared to the reaction in the non- polar solvent. CF3COOH exist as a compound containing the hydrogen ions and the electrons that are in random motion and hence, are capable to dissolve the compound into its constituents readily for the reaction. Moreover, CF3COOH have the compatible features that provide suitable space for the reaction of the compound. However, this compound reacts relatively slowly when placed in the non-polar solvent because in the non-polar solvent there molecules coexist as the molecules that are hold tightly by the covalent bonds. So it is these covalent bonds that impede the reaction to take place at a faster rate as they provide minimal space for the interaction of the atoms and movement. Hence, there is few hydrogen molecules and atoms available for reaction. Thus most of the molecules moves at a slow pace and the collision between the molecules also take place at a lower frequency. Consequently, all these factors make the reaction to occur at a very slow rate as compared to the reaction when placed in the CF3COOH. 4. A key step in the synthesis of the bacterial toxin coronafacic acid is shown below. It involves three sequential Pericyclic reactions. Identify them! The first step is photochemical cyclocoronafacic. This step is then followed by the cycloreversion. The final step which entails the transfer of hydrogen is the sigmatropic rearrangement. Sigmatropic rearrangement can either take the form of the thermal antarafacial or photochemical suprafacial. In either process the final product is the similar. 5. Explain the mechanistic significance of the product distributions shown below. The major significant of this kind of product distribution is that it aids in the identification of the alternatives sites of the attachment of the functional group within a particular reaction. The attachment of the functional group on the available points by the similar functional group results in the development of the legitimate isomers. This reaction mainly takes place through the process regioselective. Regioselective mainly takes place with the aid of the light that consequently results into the instigation of the kinetic energy. Kinetic energy is the determinate of the place of the attachment of the functional group. This is because is helps in the faster movement and the identification of sites which is more prone to attachment of the particular functional group in relative to the other existing sites. The identification of the alternatives sites of attachment can be improved through the alteration and modification of the existing experiments apparatus and conditions. These alterations and modification of the outlined experimental conditions normally results to speeding of the rate of the reactions thereby making it easy to the identification of the next alternative attachment and hence naming of the resultant isomers. Therefore, the faster functional group will reach the attachment site first thereby forming the conditional isomer. Amid the above figures, the one that exhibit and hold the higher ration proportion would form the required legal isomer. This is because it has the higher proportion in terms of ration as compared to the second structure. For instance, the ratio of 5.4 to 1.0 is greater than 4.0 to 1.0. 6. Is the closure of the trimethylene diradical to cyclopropane in its ground state conrotatory or disrotatory? Explain in terms of MO diagrams. The conversion of the trimethylene diradical to a form of the cyclopropane within its ground state is conrotatory. This is because is thermally allowed in the ground state thus the resultant product is symmetry with odd figure as the total number. Hence, the arrow changes to point the above direction. Moreover, heating a conjugate pi system has no enough energy that is capable of moving electrons into the excited state. Generally the reaction which involves the ground state is grouped under the cycloaddition reaction. 7. Draw the product(s) expected from (i) Photochemical (ii) Thermal cyclisation of (2Z, 4E) ‐heptadiene Read More