Secondary orbital overlap favors the endo product

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Secondary orbital overlap favors the endo
product formation
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O
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Ultraviolet Excitation
The amount of energy absorbed corresponds to the
energy necessary to promote an electron from one
orbital to another.
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Energy Gap Smaller for a Conjugated System
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E hv ?

• Energy gap decreases with conjugation
• Wavelength increases with conjugation

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The lmax increases as the number of conjugated
double bonds increases
?max(nm)
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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 ?
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Sunscreen
The best sunscreens block - UVB (315 and 220
nm)- which causes sunburn - UVA (380-315 nm)-
damages skin without causing sunburn
oxybenzone- blocks UVB
PABA
These conjugated dienes absorb high energy UV
radiation and release the energy as low-energy
waves.
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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

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Visible Region of Electromagnetic Spectrum
(400-800 nm)
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11 double bonds in conjugation, ?max 455 nm
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Benzene

• A planar molecule

• Has six identical carboncarbon bonds

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Resonance Contributors and the Resonance Hybrid
Resonance contributors are imaginary, but the
resonance hybrid is real
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Methampetamine (speed)
aspirin
Diflucan
Paxil
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