Secondary orbital overlap favors the endo product formation

O

Ultraviolet Excitation Only organic compounds with  electrons can produce UV spectra A UV spectrum is obtained if UV light is absorbed The amount of energy absorbed corresponds to the energy necessary to promote an electron from one orbital to another.

Energy Gap Smaller for a Conjugated System

E = hv λ Energy gap decreases with conjugation Wavelength increases with conjugation

The max increases as the number of conjugated double bonds increases λ max (nm)

UV Spectroscopy Provides information about the nature of the conjugated system. -highly conjugated systems absorb lower energy radiation -therefore, conjugated systems absorb at a longer wavelength E = hv λ

Sunscreen oxybenzone- blocks UVB PABA The best sunscreens block: - UVB (315 and 220 nm)- which causes sunburn - UVA ( nm)- damages skin without causing sunburn These conjugated dienes absorb high energy UV radiation and release the energy as low-energy waves.

Sunscreen SPF 10 = (10-1)/10 = 90% UVB blocked SPF 20 = (20-1)/20 = 95% UVB blocked SPF 30 = (30-1)/30 = 96.7% UVB blocked SPF 60 = (60-1)/60 = 98.3% UVB blocked

Visible Region of Electromagnetic Spectrum ( nm)

11 double bonds in conjugation, λ max = 455 nm

Benzene A planar molecule Has six identical carbon–carbon bonds Each  electron is shared by all six carbons The  electrons are delocalized

Resonance Contributors and the Resonance Hybrid Resonance contributors are imaginary, but the resonance hybrid is real

Methampetamine (speed) aspirin Paxil ® Diflucan