Your sister, high school is so deep now ~ the nitrogen-containing six-membered ring in the lower right corner is called piperidine, which can be regarded as the product of pyridine hydrogenation. 2 and 6 are numbers because they start with n 1 Oxo refers to the position of two carbonyl groups, because this piperidine is regarded as a substituent, so it is not written as piperidine-2,6-dione. 3- radical means that the 3- position is substituted and added to isoindole. This 3-position is chiral because four different groups are attached to the 3-position carbon atom. However, thalidomide is a pair of racemates, which is a mixture of R type and S type 1: 1. Generally written as r/s.

As for that 2H, you go and search for hydrogen and hydrogenation. There should be no problem.

Thalidomide is an important event in the history of medicinal chemistry. Good luck.