The visible spectrum of b-carotene (C40H56, MW 536.89, the

Chapter 20, Problem 20.16

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The visible spectrum of b-carotene (C40H56, MW 536.89, the orange pigment in carrots) dissolved in hexane shows intense absorption maxima at 463 nm and 494 nm, both in the blue-green region. Because light of these wavelengths is absorbed by b-carotene, we perceive the color of this compound as that of the complement to blue-green, namely, red-orange. (a) (b) (c) 200 300 400 500 600 900 nm 700 800 200 300 400 500 600 900 nm 700 600 nm 575 nm 560 nm 540 nm 525 nm 650 nm 510 nm 465 nm 495 nm 405 nm Colored arrows are complementary 800 Figure 20.5 (a) Visible light color-wavelength correlation. (b) Approximate color of substance (refl ected light) if a single wavelength (i.e. the wavelength listed on the numerical scale of the x-axis) is absorbed. (c) Complementary colors on a color wheel. 20.3 UV-Visible Spectroscopy 823 -Carotene max 463 nm (log 5.10); 494 nm (log 4.77) Calculate the concentration in milligrams per milliliter of b-carotene that gives an