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Related Concept Videos

UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in the...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
UV–Vis Spectroscopy: Woodward–Fieser Rules01:29

UV–Vis Spectroscopy: Woodward–Fieser Rules

UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...

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Changes in chromatic pattern-onset VEP with full-body inversion.

Jennifer Highsmith1, Michael A Crognale

  • 1Department of Psychology, University of Nevada, Reno, 89557, USA. highsmit@unr.nevada.edu

Documenta Ophthalmologica. Advances in Ophthalmology
|March 21, 2009
PubMed
Summary
This summary is machine-generated.

Full-body inversion increases intra-ocular pressure (IOP) and can affect vision. This study found that chromatic and achromatic pattern-onset visual evoked potentials (VEPs) showed increased latencies during inversion, indicating physiological changes in visual pathways.

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Area of Science:

  • Neuroscience
  • Ophthalmology
  • Human Physiology

Background:

  • Intra-ocular pressure (IOP) elevation, as seen in glaucoma, can be simulated by full-body inversion.
  • Previous studies using achromatic pattern-reversal VEPs showed reduced response amplitudes during inversion.
  • Chromatic pattern-onset VEPs are sensitive indicators of ocular and systemic conditions.

Purpose of the Study:

  • To investigate changes in visual pathway response latency using chromatic pattern-onset VEPs during full-body inversion.
  • To assess the impact of simulated high IOP and negative g-forces on visual processing.

Main Methods:

  • Employed chromatic and achromatic pattern-onset VEPs in 7 healthy subjects.
  • Used 1 cpd horizontal sine-wave patterns presented in onset mode (100 ms on/400 ms off) via LCD goggles.
  • Equated low to medium contrast levels across S, LM, and achromatic pathways.

Main Results:

  • A statistically significant increase in latency was observed for the CII component in both L-M and S-(L+M) chromatic pathways during inversion.
  • The CI component of the achromatic pathway also demonstrated a statistically significant increase in latency.
  • These latency changes were consistent across all subjects.

Conclusions:

  • Full-body inversion leads to measurable changes in visual pathway function.
  • Increased latencies in chromatic and achromatic pattern-onset VEPs indicate physiological alterations during inversion.
  • VEPs are sensitive to the effects of inversion on ocular and systemic physiology.