Professor Bahde's Organic Chemistry

The learning assistants for Professor Bahde’s Organic Chemistry I class, Allyson Dang and I, wanted to give the students a problem to work on involving a reaction mechanism. The students in that class have been struggling in many areas of the subject, but the main issue they have is drawing out reaction mechanisms. Knowing how to draw out reaction mechanisms is one of the most, if not the most important part of organic chemistry. When theoretically reacting molecules, one must know not only which molecules react with which, but also which parts of the molecules react with others. Based on their passed test scores, the students really need to work on learning how to draw these mechanisms or they will continue to fail the course. The problem …show more content…
The students made many different attempts at tackling this problem, and unfortunately most of their attempts were completely wrong. I was shocked by how many students didn’t understand how to apply what they learned in class on the assessment. All the tools needed to do well on the assessment were given in lecture multiple times. To start, students would correctly protonate the styrene with the sulfuric acid, but after the carbocation was formed, they would use the electrons from the negative charge of the oxygen in the HSO4- to attack the carbocation. As stated before, the correct way of going about this is having water attack the molecule. After attaching the HSO4 to the molecule, they would break off a bisulfate ion (HSO3-) leaving a negative oxygen on the product molecule. Then the students drew the oxygen taking a hydrogen from water or a new sulfuric acid molecule. The issue with this is that breaking the bond between a sulfur and an oxygen would be impossible under those conditions because that bond is too strong to break. Although this would be completely wrong, I can see how some students may have come to that conclusion. The students know that in the product they need an OH, and that after protonating the styrene it will have a positive charge while the acid they used will have a negative charge. From looking at that, they think that the positing and negative charges would combine to form a …show more content…
It is important to know where the electrons are moving in order to know how to make the final products. A very common mistake made in this assessment was made by many students in drawing the arrows when protonating the styrene. The correct way (seen in Figure 2 on page 2) is to show the electrons in the double bond of the styrene abstracting the proton from the sulfuric acid, so the arrow would go from the double bond (nucleophile) pointing to a hydrogen of the sulfuric acid (electrophile). It is important to understand that the arrow will always go from the nucleophile to the electrophile. The electrons of the nucleophile will always attack the protons of the electrophile. A few students did the exact opposite, drawing the arrow from the hydrogen to the double bond. Students must be thinking that since a hydrogen is being added to the styrene, that the arrow must show the hydrogen is moving in the direction toward the double bond. In thinking like this, it shows the students are not paying attention in class or are doing practice problems incorrectly. During our lecture, office hours, and review sessions, we cover these problems multiple times. The repetition of drawing the arrows should stick with them while doing the assessment. Since it did not for a few students, it shows they