\( \begin{array}{ll}\text { 3.46. } & \text { 3-clorobut-2-enal } \\ \text { 3.47. } & \text { 2-metilciclopentanol } \\ \text { 3.48. } & \text { butanamida } \\ \text { 3.49. } & \text { Ácido acético (ácido etanoico) }\end{array} \)

3-clorobut-2-enal is an interesting compound often used in organic synthesis due to its reactive carbonyl group and the presence of a double bond, which can lead to various reactions, including forming larger complex molecules or functionalized linkers in more elaborate drug designs. The chlorinated structure also allows chemists to introduce and manipulate synthetic routes more efficiently! 2-metilciclopentanol, on the other hand, is significant in studying cyclic compounds and their reactions. This compound can showcase unique properties like increased reactivity due to ring strain, making it a key player in organic reactions. Additionally, its structure offers insights into the behavior of alcohols and serves as a relevant compound in fragrance and flavor chemistry – proof that even the simplest structures can have delightful applications!