Which spectroscopy identifies chemical groups via dipole vibrations?
Infrared spectroscopy identifies chemical moieties by probing vibrational transitions that modulate molecular dipole moment. Each functional group possesses characteristic bond strengths and reduced masses, producing specific absorption frequencies; amide I carbonyl near 1650 cm-1 reports protein backbone, hydroxyl near 3400 cm-1 reports sugars. Circular dichroism measures differential circular polarization for chirality, X-ray diffraction measures atomic coordinates from lattice scattering, ultraviolet spectroscopy excites electronic transitions. IR uniquely requires no labeling, operates on small samples, and detects polar group vibrations, making it powerful for rapid screening of biochemical composition and hydrogen bonding networks.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.