explains how atoms combine to form molecules, providing insights into chemical bonding and reactivity. It describes how atomic orbitals merge to create molecular orbitals, where electrons reside in molecules instead of individual atoms.
This theory is crucial for understanding biomolecular structures and interactions. It helps explain protein folding, DNA base pairing, and enzyme function. In bioengineering, it's used to design drugs, engineer enzymes, and develop new biomaterials.
Fundamentals of Molecular Orbital Theory
Principles of molecular orbital theory
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Molecular Orbital (MO) Theory describes electronic structure of molecules combines atomic orbitals to form molecular orbitals where electrons reside instead of atomic orbitals
(LCAO) mathematically combines atomic wave functions to create molecular orbitals
Bonding and antibonding orbitals form when atomic orbitals interact constructively or destructively
Energy level diagrams visually represent molecular orbital energies and electron occupancies
Sigma (σ) orbitals result from head-on overlap of atomic orbitals (single bonds)
Pi (π) orbitals form from side-by-side overlap of p orbitals (double and triple bonds)
Construction of molecular orbital diagrams
Construct MO diagrams:
Identify valence electrons and atomic orbitals of constituent atoms
Determine molecular symmetry to predict orbital interactions
Combine atomic orbitals to form molecular orbitals based on symmetry and energy
Fill molecular orbitals with electrons following Aufbau principle and Hund's rule
Interpret MO diagrams:
Calculate using formula (bonding−antibonding)/2 to predict stability
Determine magnetic properties based on unpaired electrons (paramagnetic or diamagnetic)
Examples:
Homonuclear diatomics (H₂, O₂, N₂) show symmetrical orbital combinations
Heteronuclear diatomics (CO, NO) display asymmetric orbital mixing
Triatomic molecules (H₂O, CO₂) involve multiple atomic orbital interactions
Molecular orbitals in biomolecular structure
Electronic structure of biomolecules shapes protein secondary structures (α-helices, β-sheets) and DNA base pairing
MO theory explains biomolecular interactions through hydrogen bonding, van der Waals forces, and π-π stacking in nucleic acids
Spectroscopic techniques utilize MO theory principles:
UV-Vis spectroscopy probes electronic transitions between molecular orbitals
Fluorescence spectroscopy examines excited state relaxation processes