Dr. Sunil Kumar is a well-rounded researcher with more than 20 years of experience in leading, supervising and undertaking research in the broader field of Environmental Engineering and Science with focus on Solid and Hazardous Waste Management. He has contributed extensively to these fields and has h-index of 30 and i10-index of 43 (Google scholar); highly impressive for a non-academic researcher from India. His contributions since inception at CSIR-NEERI in 200 include 130 refereed journal publications, 04 books and 25 book chapters, 08 Edited volumes and numerous project reports to various governmental and private, local and International academic /research bodies. The list of his collaborations is long and includes key Indian universities, such as IIT Kharagpur, IIT Delhi and IIT Mumbai and prestigious regional institutes, such as Asian Institute of Technology (AIT) and Kasetsart University in Bangkok, Hong Baptist University as well as universities in US (Columbia, Texas A&M) and Europe (UN University and University of Uppsala). Vinod Kumar is an Assistant Professor of Chemistry at M.M.University, Mullana, Ambala, India. He qualified on the NET Examination (a highly competitive test for lectureship in India) in 2001, and obtained a PhD in 2006 under the supervision of Professors S.P. Singh and Ranjana Aggarwal. He received the Young Scientist Award of Indian Science Congress Association from the President of India for his outstanding contribution in the field of chemical sciences in 2007, and he was invited to visit Korea Atomic Energy Research Institute (KAERI), South Korea, as a Foreign Expert in 2012. His research interests focus on the structural reinvestigation, green chemistry, and synthesis of heterocyclic compounds, mainly azoles. He has published many research papers and review articles in professional journals and has filed four patents. He has served as an editor, guest editor, and reviewer for many national and international journals. S.P. Singh is Professor Emeritus, Department of Chemistry, Kurukshetra University, Haryana, India. He obtained a PhD in 1964 from University of Lucknow and joined Kurukshetra University in 1965. Singh was also associated with the University of Illinois at Chicago, USA, as a Post-Doctoral Fellow, Senior Fulbright Scholar, and Visiting Research Professor. Singh has worked in diverse areas of organic chemistry, including reaction mechanisms, organic photochemistry, mass spectrometry, and primarily, the structural reinvestigation of heterocyclylpyrazoles. He has published more than 200 research papers and reviews in professional journals. For his services in chemistry, he has received the Acharya P. C. Ray Memorial Medal and a Lifetime Achievement Award from the Indian Chemical Society. He was awarded New Millennium Plaque of Honour at the inaugural function of the Indian Science Congress in 2014.

• Preface1. Pericyclic Reactions and Molecular Orbital Symmetry2. Electrocyclic Reactions3. Sigmatropic Rearrangements4. Cycloaddition Reactions5. Cheletropic Reactions and 1,3-Dipolar Cycloadditions6. Group Transfer, Elimination, and Related Reactions7. Unsolved ProblemsAppendix: Solutions ManualIndex