Abstract: The basic concepts of organic chemistry have definite connotations and extensions under certain conditions, and their connotations and extensions change along with the development of times, the progress of science and technology and deepening understanding. It is necessary to understand the connotations and extensions of the concepts with a developmental viewpoint, so as to have a comprehensive knowledge of the concepts' formation meaning, stage characteristics and development process. For the basic concepts of chemistry with the relationship of "intersection" or "inclusion" in connotation and extension, we should use the knowledge of mathematics and other related disciplines to help us understand them. For the basic chemical concepts with similar pronunciation but different meanings, we should grasp the law of cognition and systematize the natural correlation between them. For the different expressions of the same concept in different textbooks, the connotation and extension defined by authoritative reference books shall prevail.

Key words: organic chemistry concepts, connotation, extension, dialectical understanding