Organic chemistry plays a fundamental role in the field of pharmaceutical sciences, serving as the foundation for drug discovery, synthesis, and development. Pharmaceutical Organic Chemistry-I has been meticulously crafted to meet the academic and professional needs of pharmacy students, providing them with a comprehensive understanding of organic compounds, their properties, reactions, and significance in pharmaceutical applications. This book is designed in accordance with the syllabus prescribed by PCI, New Dehli, for undergraduate pharmacy courses. It covers essential topics such as structure and bonding, reaction mechanisms, stereochemistry, and functional group chemistry, emphasizing their relevance in pharmaceutical sciences. The concepts have been presented in a systematic and simplified manner, supported by illustrative examples, reaction mechanisms, and applications in drug development. Our primary objective in writing this book is to bridge the gap between theoretical knowledge and practical applications, ensuring that students not only grasp fundamental concepts but also develop an appreciation for their role in medicinal chemistry and drug formulation. Special emphasis has been placed on clarity and conceptual understanding, making this book a valuable resource for both students and educators. We would like to express our sincere gratitude to my mentors, colleagues, and students whose encouragement and constructive feedback have contributed to the development of this book. We are also thankful to the publishers for their unwavering support in bringing this work to fruition. We hope that this book serves as an effective guide and inspires students to delve deeper into the fascinating world of pharmaceutical organic chemistry. Constructive suggestions and feedback from readers are most welcome and will be highly appreciated for further improvements in future editions.