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Lecture Organic chemistry - Chapter 14: Delocalized Pi systems. After studying this chapter you will: Be able to identify, without explicit prompting, when delocalization is important, or not, be able to discuss the special characteristics benzene, be able to predict the products from a Diels-Alder reaction and be able to recognize a set of reactants and conditions as those belonging to the Diels-Alder reaction. | Chemistry 3B The (a) view of your existence. 9/14/2014 1 © University of California In the News: A Cure for Hepatitis C Syllabus Sofosbuvir (Sovaldi) by Gilead Sciences (Foster City) approved by FDA December 2013: already a blockbuster drug >$ 5 billion in 2014 ~200 Million affected; leads to liver cirrhosis and cancer; 350,000 deaths (20,000 US) annually The phosphate serves as a defective nucleotide substrate for the viral RNA polymerase, and thus inhibits viral RNA synthesis. “Prodrug” I, too, started small Peter Vollhardt University of California at Berkeley The Fun of Organic Chemistry Tigre Delta, Buenos Aires, 1952 Chapter 14 Delocalized Pi Systems Trigonal The π bond is e-rich: E+ attack, R∙ add The lobes of the p-orbitals: Perpendicular to the sigma frame and parallel to each other. Recall the double bond EtheneF 9/14/2014 4 © University of California 2-Propenyl (Allyl) Question: What about adding a third p-orbital adjacent to the double bond? Is there something . | Chemistry 3B The (a) view of your existence. 9/14/2014 1 © University of California In the News: A Cure for Hepatitis C Syllabus Sofosbuvir (Sovaldi) by Gilead Sciences (Foster City) approved by FDA December 2013: already a blockbuster drug >$ 5 billion in 2014 ~200 Million affected; leads to liver cirrhosis and cancer; 350,000 deaths (20,000 US) annually The phosphate serves as a defective nucleotide substrate for the viral RNA polymerase, and thus inhibits viral RNA synthesis. “Prodrug” I, too, started small Peter Vollhardt University of California at Berkeley The Fun of Organic Chemistry Tigre Delta, Buenos Aires, 1952 Chapter 14 Delocalized Pi Systems Trigonal The π bond is e-rich: E+ attack, R∙ add The lobes of the p-orbitals: Perpendicular to the sigma frame and parallel to each other. Recall the double bond EtheneF 9/14/2014 4 © University of California 2-Propenyl (Allyl) Question: What about adding a third p-orbital adjacent to the double bond? Is there something special? Or: Is there any special reactivity at the carbons adjacent to a double bond? H 9/14/2014 5 © University of California a. b. c. SN1 reactivity of allylic carbon like that of RsecX, even though it is primary! pKa ~ 40: Acidic! 50 SN1 87 kcal mol-1: Weak! 101 kcal mol-1 Replacing one of the hydrogens in ethene with another sp2-hybridized carbon gives a propenylic or allylic system. Allylic position Observations: H L H B B H H 9/14/2014 6 © University of California Clearly: Allylic · are stabilized. - + Short notation: Dotted lines Why? Resonance! 9/14/2014 7 © University of California Reactivity of Allylic Position A. Radical Halogenation CH2 CHCH3 + Br2 CH2 CH CH2Br + HBr Faster than addition! Low conc. Mechanism: 1. 2. Br2 2 Br . hυ or Δ Initiation: Propagation: CH2 CHCH3 + Br . CH2 CH CH2 . CH2 CH CH2 . + HBr CH2 CH CH2 . CH2 CH CH2 . Br2 CH2 CH CH2Br + Br . or ROOR radical initiator 9/14/2014 8 © University of California Termination: 3. Br . + . CH2CH CH2 BrCH2CH CH2 Br . Br . +
