absorption maximum at wavelengths longer than 200nm. What are the structures of A and B? The answer is : A B13.8 Three compounds, D, E, and F, have the same molecular formula, C5H6. In the presence of a platinum catalyst, all three compounds absorb 3 molar equivalents of hydrogen and yield pentane. Compounds E and F have an IR absorption at roughly 3300 cm-1; compound D has no IR absorption in that region. Compounds D and E show an absorption maximum in their UV-Vis spectra near 230 nm. Compound F shows no absorption maximum beyond 200nm. Propose structures for D, E and F. The answer is: D CH3CCCHCH2
E CH3CHCHCCHF CHCH2CH2CCH13.9 (a) What product would you expect to obtain if hydrogen chloride were allowed to react with a 2,4-hexadiene , CH3CH=CHCH=CHCH3 ? (b) With 1,3-pentadiene, CH2=CHCH=CHCH3? (Neglect cis-trans isomerism.) (a) H3CHCCHCHCHCH3ClHCH3CH2CHCHCHCH3CH3CH2CHCHCHCH3CH3CH2CCHCHCH3ClababCH3CH2CHCHCHCH3ClCH3CH2CHCHHCCH3Cl(b) H2CCHCHCHCH3ClHCH3CHCHCHCH3CH3CHCHCHCH3CH3CCHCHCH3ClababCH3CHCHCHCH3ClCH3CHCHHCCH3Cl13.10 (a) Can you suggest a possible explanation for the fact that the 1,2-addition reaction of 1,3-butadiene and hydrogen bromide occurs faster than 1,4-addition? (b) How can you account for the fact that the 1,4-addition product is more stable? Answer: Clearly we can see that the free-energy needed for 1,2-addition reaction is a bit less than 1,4-addition, which means that it needs less energy, so that 1,2-addition occurs faster. On the other hand, when the reaction really takes place, 1,4-reaction releases much more free-energy than 1,2-reaction, which means that the product of 1,4-reaction is surely more stable, so if more time is given, the product of 1,4-reaction, the more stable one, must be the main product.
H2C=CH-CH=CH21,2 Addition1,4 additionFree energyHCCHCCH3Figure 13.1013.11 The dimerization of cyclopentadiene also occurs in an endo way. (a) Show how this happen. (b) which πelectron interact? (c) What is the three-dimensional structure of the product? Answer: π-electron interaction occurs here13.12 What products would you expect form the following reactions? a) +OOb) +OOOOOOOO
c) OOO+OOO13.13 Which diene and dienophile would you employ to synthesize the following compound? COOHHHCOOHAnswer: andCOOCH3HHH3COOC13.14 Diels-Alder reactions also take place with triple-bonded (acetylenic) dienophiles. Which diene and which dienophile would you use to prepare the following? COOCH3COOCH3The answer: andCOOCH3H3COOC13.15 1,3-Butadiene and the dienophile shown below were used by A. Eschenmoser in his synthesis of vitamin B12 with R. B. Woodward. Draw the structure of the enantiomeric Diels-Alder adducts that would form in this reaction, and the two transition states that lead to them.
- Spring '10
- Atom, Bromine, Nuclear magnetic resonance, Cl Cl Cl