(a) On the basis of the following data, identify unknowns A, found in fresh cream prior to churning, and B, possessor of the characteristic yellow color and buttery odor of butter. 

(b) What kind of reaction is the conversion of compound A into compound B? Does it make sense that this should take place in the churning of cream to make butter? Explain. 

(c) Outline laboratory syntheses of compounds A and B, starting only with compounds containing two carbons. 

(d) The UV spectrum of compound A has a λ_max at 271 nm, whereas that of compound B has a λ_max at 290 nm. (Extension of the latter absorption into the violet region of the visible spectrum is responsible for the yellow color of compound B.) Explain the difference in λ_max.

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A: MS: m/z (relative abundance) = 88(M*, weak), 45(100), and 43(80). 'H NMR: 8 = 1.36 (d, J = 7 Hz, 3 H), 2.18 (s, 3 H), 3.73 (broad s, 1 H), 4.22 (q, J = 7 Hz, 1 H) ppm. IR: ỹ = 1718 and 3430 cm. B: MS: m/z (relative abundance) = 86(17) and 43(100). 'H NMR: 8 = 2.29 (s) ppm. %3D IR: 5 = 1708 cm.