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Very valuable, thank you

Thank you for that lecture. I've enjoyed it a lot. That was time well spent - it made me realise the impact that stereochemistry can have on UV absorption and I have learned about the concept of vacuum UV spectroscopy.

Thank you

For the answer: Blocking Conjugation: Bulky substituents can hinder the delocalization of electrons in the conjugated system by physically blocking the alignment of π orbitals. This can result in a decrease in conjugation and thus a shift in the absorption spectrum to longer wavelengths (lower energy), as the molecule absorbs light of lower energy. Extending Conjugation: Conversely, steric effects can also extend conjugation in some cases. Bulky groups may force the molecule into a conformation that enhances π overlap and increases the extent of conjugation. This can lead to a bathochromic shift (a shift to longer wavelengths) in the absorption spectrum, indicating increased absorption at lower energies. Distorting Conjugation: Steric hindrance can distort the geometry of the conjugated system, altering bond angles and lengths. This distortion can affect the distribution of electron density within the conjugated system, potentially changing the energy levels of the π orbitals involved in absorption. Consequently, this may result in shifts in the absorption spectrum. Electronic Effects: Steric effects can also influence the electronic environment around the conjugated system by altering the electronegativity of nearby atoms or by inducing inductive effects. These electronic changes can modulate the energy levels of the π orbitals and hence affect the absorbance spectrum. Overall, the influence of steric effects on conjugation in UV-Vis absorbance spectra can be complex and depends on the specific molecular structure and arrangement of substituents. Experimental observation and computational studies are often used to understand and predict the effects of steric hindrance on conjugation and UV-Vis absorbance.

Nice lecture professor Stephens.. Thank you for the videos

What do you mean sulfur has d orbitals? Isn't the configuration for sulfur 1s22s22p63s23p4?

Good concept

how does that stirrer spin in the mixture? crazy

Note that I cut the end off of this video to omit the discussion of the formula shown at the bottom of the handout (I also removed that formula from the handout I gave you). I'f you'd like me tell you about that formula, just ask.