Topic #2: Arrange the following in order of decreasing reactivity to nucleophilic addition: ketone, aldehyde. Explain your logic. Relative Reactivity: 1.) Aldehyde (highest) 2.) Ketone (lowest) First, let’s review the structure of these two molecules. As we can see, the general formula for an aldehyde is RCHO, whereas the general formula for a Ketone is R2CO. The difference between these two molecules is that Ketones have an extra alkyl substituent compared to aldehyde, which has a hydrogen instead. The implication is that aldehydes and ketones will differ sterically and electronically. When we examine the structural differences between these molecules, we see that ketones are more sterically hindered than aldehydes. This makes it more difficult for nucleophiles to attack ketones compared to aldehydes. Our course textbook, Organic Chemistry with Biologic Applications notes that “the transition state leading to the tetrahedral intermediate is less crowded and lower in energy for an aldehyde than for a
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