DiscussionThe reaction of (-)-α-phellandrene, 1, and maleic anhydride, 2, gave a Diels-Alder adduct, 4, 7- ethanoisobenzofuran- 1, 3- dione, 3a, 4, 7, 7a- tetrahydro- 5- methyl- 8- (1- methylethyl), 3, this reaction gave white crystals in a yield of 2.64 g (37.56%). Both hydrogen and carbon NMR, as well as NOESY, COZY and HSQC spectra were used to demonstrate that 3 had formed. These spectroscopic techniques also helped identify whether the process was attacked across the upper or lower face, as well as whether this reaction occurred via the endo or exo process. These possible attacks give rise to four possible products, however, in reality only one product is formed due to steric interactions and electronics.Scheme 1. Formation of the Diels-Alder adduct with maleic anhydride and (-)-α-phellandrene .The IR spectrum obtained from the white crystals showed different functional groups present in the molecule. The spectrum shows a weak and sharp peak between 2865 and 2964 cm-1, which is often associated with CH, sp3 hybridization, stretching in the molecule, peaks in this region often represent a methyl group or CH2 groups. There are also peaks at 1369 cm-1, which is associated with CH3 stretching. There is also a C=O stretch at 1767 cm-1, which is a strong peak due to the large dipole created through the large electronegativity difference of the carbon and oxygen atom. An anhydride CO resonates between 1000 and 1300 cm-1 this is at least two bands. The peak is present in the 13C NMR at 1269 and 1299 cm-1 and is of medium intensity. Figure 1. 3-labeled atoms used in NMR assignment. The 1H NMR spectrum shows that there are 18 protons in 11 different proton environments. This fits with the Diels-Alder reaction that takes place in the......middle of paper......interaction between the HOMO of the diene and the LUMO of the dienophile. This reaction was carried out at relatively low temperatures since dry ether has a boiling point of 34.6 °C. At low temperatures the endo preference predominates unless there is an extreme steric hindrance, which in this case there is not. The endo product is formed almost exclusively because the activation barrier for endo is much lower than that for exo. This means that the endo form forms faster. When reactions proceed through the endo, the reaction is under kinetic control. Under kinetic control the adduct is more sterically congested, therefore thermodynamically less stable. The endo form has a lower activation energy, however the EXO form has a more stable product. Since this is a symmetric Diels-Alder reaction, there are no two possible isomers of the product. Figure 5. Mechanism of formation of 3.