3 public questions tagged with this topic.
[Ni(H₂O)6]2+ (Ni₂+, d8) in an octahedral field has t2g6 eg2, and the d-d transition from t2g to eg absorbs visible light (green color).
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Isomerism - Geometrical Isomerism in Coordination Compounds
Electromagnetic spectrum couples with distinct molecular energy levels. Microwave photons induce rotational transitions, infrared photons drive vibrational stretching and bending, X-rays eject inner core electrons causing ionization. Outer valence electrons from bonding π, nonbonding n to antibonding π*, σ* orbitals require photon energies approximately two to seven electron volts corresponding to wavelength range 200-800 nm, spanning ultraviolet and visible region. Consequently colored biomolecules, conjugated cofactors such as heme, carotenoids, chlorophyll, flavins and aromatic amino acids and nucleic acid bases absorb in UV-Visible region, enabling spectrophotometric analysis of biochemical reactions and purity.
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.
Electronic transitions require distinct excitation energies determined by orbital energy gaps. σ–σ* involves strongly bonded electrons with very large separation, absorbing in vacuum UV below 150 nm. n–σ* is intermediate, involving lone pair to antibonding sigma orbitals around 150-200 nm. π–π* conjugated systems and n–π* have smallest gaps, appearing in near UV 200-300 nm. Therefore decreasing energy follows σ–σ* highest, then n–σ*, then π–π*, with n–π* lowest. This energetic hierarchy explains why biomolecular spectra show peptide backbone in far UV and aromatic, nucleic acid absorptions in near UV.
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.
