126 - Practice Problem 1-26 Answer How many absorptions...

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Practice Problem 1-26 Answer How many absorptions would you expect to observe in the 13 C NMR spectra of the following compounds? (a) 1,1-Dimethylcyclohexane (b) tert -Butylcyclohexane (c) cis -1,2-Dimethylcyclohexane (d) CH 3 CH 2 OCH 3 (e) 3-Methyl-1-pentyne (f) Practice Problem 1-27 Answer The isomers 3-heptanol (A ) and 4-heptanol (B ) are difficult to distinguish by either their IR or 1 H NMR spectra. The proton-decoupled 1 3 C NMR spectra of these compounds are given below. Indicate which compound goes with each spectrum, and explain your reasoning. Spectrum #1 only contains 4 signals, while Spectrum #2 has 7 signals. When the number of signals in a 13 C NMR spectrum is smaller than the number of C atoms in the molecule, there must be an element of symmetry within the structure which causes some of the carbon atoms to be equivalent to each other. If we draw the structures of 3- heptanol and 4-heptanol and label the different kinds of C atoms with letters, we can see that 4-heptanol has symmetry, while 3-heptanol does not. Spectrum #1 therefore corresponds to 4-heptanol, while Spectrum #2 corresponds to 3-heptanol. a b c d a c d e 5 absorptions a b f d a c d e a e 6 absorptions a b d a c d b c 4 absorptions 3 absorptions a b c f a d e b c 6 absorptions O a b b c d c 4 absorptions a b c d OH e f g 3-Heptanol OH a b b c c d d 4-Heptanol
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Practice Problem 1-28 Answer Following are structural formulas for three constitutional isomers with the molecular formula C
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This note was uploaded on 10/25/2010 for the course CH 310n taught by Professor Iverson during the Summer '08 term at University of Texas.

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126 - Practice Problem 1-26 Answer How many absorptions...

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