It's difficult to sustain intense effort for long periods of time. Give yourself a break. Switch to some other kind of activity. Don't hurry, but don't stop . Learning occurs in spurts and from time to time there will be a plateau.
Regular effort is likely to be more effective than concentrated effort.
You want to practice perfection. Perhaps this has less direct application in Ochem and is one way perhaps that science is different from music. Todd Gitlin, an NYU professor was writing about a new web service that is posting free class notes from courses at 62 universities. Professor Gitlin reflected on his experience with a note-taking service when he was teaching at the University of California, Berkeley. While on sabbaticals at the University of California, San Diego, I've had similar note-takers in the classes that I taught.