Final answer:
To identify a Lewis base in an organic reaction, look for organic compounds like amines that have a lone pair of electrons available for donation, as these electron pairs can be donated to form a Lewis acid-base adduct.
Step-by-step explanation:
The student is inquiring about identifying a compound that would act as a Lewis base in an organic reaction. According to Lewis theory, a Lewis base is an electron-pair donor. Amongst organic compounds, amines, such as ethylamine (CH3CH2NH2), are common examples of substances that can act as Lewis bases as they have a lone pair of electrons that can be donated to form an acid-base adduct with a Lewis acid, such as in the reaction of boron trifluoride with ammonia. Conversely, nonmetal oxides are typically Lewis acids that are electron deficient and react with a Lewis base to form oxyanions.
Therefore, when looking for a Lewis base in an organic reaction, compounds that contain nitrogen with a lone pair, such as amines, or oxygen atoms with lone pairs, such as ethers, are likely candidates. In this context, the given examples include boron trifluoride-ammonia adduct, and ethylamine (CH3CH2NH2) is identified as a weak base capable of acting as a Lewis base due to the presence of a lone pair on the nitrogen atom.