resonance structure

(noun)

A molecule or polyatomic ion that has multiple Lewis structures because bonding can be shown multiple ways.

Related Terms

  • resonant structures
  • resonance
  • formal charge
  • octet rule

(noun)

A way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by a single Lewis structure.

Related Terms

  • resonant structures
  • resonance
  • formal charge
  • octet rule

Examples of resonance structure in the following topics:

  • Resonance

    • Resonance structures depict possible electronic configurations; the actual configuration is a combination of the possible variations.
    • Each contributing resonance structure can be visualized by drawing a Lewis structure; however, it is important to note that each of these structures cannot actually be observed in nature.
    • Therefore, three valid resonance structures can be drawn.
    • Sometimes, resonance structures involve the placement of positive and negative charges on specific atoms.
    • Because atoms with electric charges are not as stable as atoms without electric charges, these resonance structures will contribute less to the overall resonance structure than a structure with no charges.
  • Peptide Bonding between Amino Acids

    • Higher-ordered structures such as peptide chains and proteins are formed when amino acids bond to each other.
    • The amide group has three resonance forms, which confer important properties.
    • First, the stabilization afforded from the resonance structures effectively stabilizes it by 80kj/mol, making it less reactive than similar groups.
    • The peptide bond is uncharged at normal pH values, but the double bonded character from the resonance structure creates a dipole, which can line up in secondary structures.
  • Resonance

    • This averaging of electron distribution over two or more hypothetical contributing structures (canonical forms) to produce a hybrid electronic structure is called resonance.
    • Likewise, the structure of nitric acid is best described as a resonance hybrid of two structures, the double headed arrow being the unique symbol for resonance.
    • The application of resonance to this case requires a weighted averaging of these canonical structures.
    • The basic principles of the resonance method may now be summarized.
    • On the other hand, if two or more canonical forms have identical low energy structures, the resonance hybrid will have exceptional stabilization and unique properties.
  • Acidity of Phenols

    • A similar set of resonance structures for the phenolate anion conjugate base appears below the phenol structures.
    • The resonance stabilization in these two cases is very different.
    • An important principle of resonance is that charge separation diminishes the importance of canonical contributors to the resonance hybrid and reduces the overall stabilization.
    • The contributing structures to the phenol hybrid all suffer charge separation, resulting in very modest stabilization of this compound.
    • An energy diagram showing the effect of resonance on cyclohexanol and phenol acidities is shown below.
  • NMR and MRIs

    • Magnetic resonance imaging is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
    • Magnetic resonance imaging (MRI), also called nuclear magnetic resonance imaging (NMRI) or magnetic resonance tomography (MRT), is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
    • MRI utilized the property of nuclear magnetic resonance (NMR) to image the nuclei of atoms inside the body.
    • This electromagnetic field has just the right frequency (known as the resonance frequency) to become absorbed and then reverse the rotation of the hydrogen protons in the magnetic field.
  • Structural Determination

    • Structural determination using isotopes is often performed using nuclear magnetic resonance spectroscopy and mass spectrometry.
    • Structural determination utilizing isotopes is often performed using two analytical techniques: nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS).
    • Nuclear magnetic resonance and mass spectrometry are used to investigate the mechanisms of chemical reactions.
    • NMR and MS detect isotopic differences; detecting these differences allows information about the position atoms in a product's structure to be determined.
    • Identify the uses of isotopic labeling in structural determination and the primary techniques used to study isotopically-labeled molecules
  • Reactions of Fused Benzene Rings

    • Naphthalene is stabilized by resonance.
    • Three canonical resonance contributors may be drawn, and are displayed in the following diagram.
    • The two structures on the left have one discrete benzene ring each, but may also be viewed as 10-pi-electron annulenes having a bridging single bond.
    • The structure on the right has two benzene rings which share a common double bond.
    • This contrasts with the structure of benzene, in which all the C–C bonds have a common length, 1.39 Å.
  • Forced Vibrations and Resonance

    • The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
    • The phenomenon of driving a system with a frequency equal to its natural frequency is called resonance.
    • It is interesting that the widths of the resonance curves shown in depend on damping: the less the damping, the narrower the resonance.
    • Heavy cross winds drove the bridge into oscillations at its resonant frequency.
    • The damping decreased when support cables broke loose and started to slip over the towers, allowing increasingly greater amplitudes until the structure failed.
  • The Chemical Shift

    • Although the eleven resonance signals are distinct and well separated, an unambiguous numerical locator cannot be directly assigned to each.
    • Also, it should give a single sharp nmr signal that does not interfere with the resonances normally observed for organic compounds.
    • Note that νref is the resonant frequency of the reference signal and νsamp is the frequency of the sample signal.
    • The hydrogen atoms in a given molecule are all structurally equivalent, averaged for fast conformational equilibria.
    • The first feature assures that each compound gives a single sharp resonance signal.
  • Signal Strength

    • From one of the spectrum signals (colored red) or on hydrogen atom(s) in the structural formulas the spectrum, a diagram follows showing an enlarged spectrum and the relationship will be colored blue.
    • Hydrogen bonding shifts the resonance signal of a proton to lower field ( higher frequency ).
    • Two structurally equivalent structures may be drawn for the enol tautomer (in magenta brackets).
    • For most of the above resonance signals and solvents the changes are minor, being on the order of ±0.1 ppm.
    • However, two cases result in more extreme changes and these have provided useful applications in structure determination.
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