Acid-base chemistry is a foundational concept for organic chemistry, and the complexities in teaching and learning acid-base chemistry are well documented. This study aimed to investigate post-secondary instructors' pedagogical content knowledge (PCK) for teaching acid-base chemistry in an organic chemistry context. Two groups of three graduate teaching assistants and one group of three faculty instructors constructed content representations (CoRes). The three CoRes generated by these groups were qualitatively analyzed and organized into a summary compiled CoRe. Analysis of the compiled CoRe revealed eight major concepts of organic acid-base chemistry as defined by these instructors. Three major concepts were identified as foundational definitions, and five were identified as concepts that build upon these definitions. We arranged all eight concepts into a progression. Analysis of the compiled CoRe also revealed that instructors primarily leverage students' prior knowledge when teaching acid-base chemistry. Our results serve as a reference for organic chemistry instructors and may inform further research on the instruction of organic chemistry.