Microwave spectroscopy and nuclear magnetic resonance spectroscopy--what is the connection?

The history and development of microwave spectroscopy and nuclear magnetic resonance (NMR) spectroscopy have much in common. In this Account, we discuss the less widely appreciated connections between the parameters measured using the two techniques. Selected examples from our laboratory and from the recent literature attest to the utility and importance of these connections. For example, how are nuclear spin-rotation tensors and NMR chemical shifts related? Why should chemists be interested in absolute magnetic shielding scales? What can chemists learn about trends in spin-spin coupling constants from the hyperfine parameters measured in microwave and molecular beam experiments? The increasingly important role of quantum-chemical calculations in the interpretation of the microwave and NMR data is also highlighted.