7_all_ - 7.1 Using the (E)-(Z) designation [and in parts...

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7.1 Using the (E)-(Z) designation [and in parts (e) and (f) the (R-S) designation as well], give IUPAC names for each of the following. CC Cl Br H CH 2 CH 2 CH 3 (a) H 3 C H CH 2 CH(CH 3 ) 2 CH 3 (b) Cl I Br CH 2 CH 3 (c) Cl I CH 3 CH 2 CH 3 (d) C H 3 C H CH 3 C CH 3 H (e) C Br H Cl C H 3 C H (f) Answer: (a) (Z)-1-Bromo-1-chloro-1-pentene (b) (Z)-3,5-Dimethyl-2-hexene (c) (E)-2-Bromo-1-chloro-1-iodo-1-butene (d) (Z)-1-Chloro-1-iodo-2-methyl-1-butene (e) (2Z,4S)-3,4-Dimethyl-2-hexene (f) (1Z,3R)-1-Bromo-2-chloro-3-methyl-1-hexene 7.2 Heats of hydrogenation of three alkenes are as follows: 2-methyl-1-butene (-119kJ/mol) 3-methyl-1-butene (-127kJ/mol) 2-methyl-2-butene (-113kJ/mol) (a) Write the structure of each alkene and classify it as to whether its doubly bonded atoms are monosubstituted, disubstituted, trisubstituted, or tetrasubstituted. (b) Write the structure of the product formed when each alkene is hydrogenated. (c) Can heats of hydrogenation be used to relate stabilities of these three alkene? (d) If so, what is the predicted order of stability? If not, why not? (e) What other alkene isomers are possible for these alkenes? Write their structures. (f) What data would be necessary to relate the stabilities of all these isomers? Answer: (a) 2-methyl-1-butene disubstituted 3-methyl-1-butene monosubstituted
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2-methyl-2-butene trisubstituted (b) 2-methyl-butane (c) Yes. Because the products are the same. (d) stability: 3-methyl-1-butene<2-methyl-1-butene<2-methyl-2-butene (e) 1-pentene 2-pentene (f) heats of combustion and heats of hydrogenation. 7.3 Predict the more stable alkene of each pair. (a) 2-Methyl-2-pentene or 2,3-dimethyl-2-butene, (b) cis -3-hexene or trans -3-hexene, (c) 1-hexene or cis -3-hexene, and (d) trans -2-hexene or 2-methyl-2-pentene. Answer: (a) 2,3-dimethyl-2-butene , (b) trans -3-hexene , (c) cis -3-hexene , (d) 2-methyl-2-pentene are more stable alkenes of each pair. 7.4 Consider the pairs of alkenes, for which pairs could you use heats of hydrogenation to determine their relative stabilities? For which pairs would you be required to use heats of combustion? (a) 2-methyl-2-pentene or 2,3-dimethyl-2-butene, (b) cis -3-hexene or trans -3-hexene, (c) 1-hexene or cis -3-hexene, (d) trans -2-hexene or 2-methyl-2-pentene Answer: To both (b) and (c), we could use heats of hydrogenation to analysis their relative stability, to (a) and (d), we need to use heats of combustion to analysis their relative stabilisty. 7.5 List the alkenes that would be formed when each of the following alkyl halides is subjected to dehydrohalogenation with potassium ethoxide and use Zaitsev’s rule to predict the major product of each reaction: (a) 2-bromo-3-methylbutane and (b) 2-bromo-2,3-dimethylbutane. Answer: (a) 2-bromo-3-methylbutane KOCH 2 CH 3 + Br CH 3 CH 2 OH major minor
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(b) 2-bromo-2,3-dimethylbutane. Br KOCH 2 CH 3 CH 3 CH 2 OH + major minor 7.6 Consider a simple molecule such as ethyl bromide and show with Newman projection formulas how the anti periplanar state would be favored over the syn periplanar one.
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7_all_ - 7.1 Using the (E)-(Z) designation [and in parts...

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