Organic Structures from Spectra. H. L. Li

courses have been taught in the second and third years of undergraduate chemistry, at which stage students have usually completed an elementary course of Organic Chemistry in their first year and students have also been exposed to elementary spectroscopic theory, but are, in general, unable to relate the theory to actually solving spectroscopic problems.

      We have delivered courses of about 9 lectures outlining the basic theory, instrumentation and the structure–spectra correlations of the major spectroscopic techniques. The treatment is highly condensed and elementary and, not surprisingly, the students do initially have great difficulties in solving even the simplest problems. The lectures are followed by a series of problem solving workshops (about 2 hours each) with a focus on 5 to 6 problems per session. The students are permitted to work either individually or in groups and may use any additional resource material that they can find. At the conclusion of the course, the great majority of the class is quite proficient and has achieved a satisfactory level of understanding of all methods used. Clearly, most of the real teaching is done during the hands-on problem seminars. At the end of the course, there is an examination usually consisting essentially of 3 or 4 problems from the book and the results are generally very satisfactory. The students have always found this a rewarding course since the practical skills acquired are obvious to them. Solving these real puzzles is also addictive – there is a real sense of achievement, understanding and satisfaction, since the challenge in solving the graded problems builds confidence even though the more difficult examples are quite demanding.

      Problems 1–19 are introductory questions designed to develop the understanding of molecular symmetry, the analysis of simple spin systems as well as how to navigate the common 2D NMR experiments.

Problems 20–294 are of the standard “structures from spectra” type and are arranged roughly in order of increasing difficulty. A number of problems deal with related compounds (sets of isomers) which differ mainly in symmetry or the connectivity of the structural elements and are ideally set together. The sets of related examples include Problems 33 and 34; 35 and 36; 40–43; 52 and 53; 57–61; 66–71; 72 and 73; 74–77; 82 and 83; 84–86; 92–94; 95 and 96; 101 and 102; 106 and 107; 113 and 114; 118–121; 126 and 127; 129–132; 133 and 134; 137–139; 140–142; 154 and 155; 157–164; 165–169; 176–180; 185–190; 199–200; 205–206; 208–209; 211–212; 245–247; 262–264; and 289–290.

      A number of problems (218, 219, 220, 221, 242, 273, 278, 279, 280, 285, 286 and 287) exemplify complexities arising from the presence of chiral centres, and some problems illustrate restricted rotation about amide bonds (191, 275 and 281). There are a number of problems dealing with the structures of compounds of biological, environmental or industrial significance (41, 49, 64, 91, 92, 93, 94, 98, 146, 151, 152, 160, 179, 180, 191, 198, 219, 225, 231, 235, 236, 269, 285, 277, 278, 279, 284, 286 and 287).

      Problems 295–300 are again structures from spectra, but with the data presented in a textual form such as might be encountered when reading the experimental section of a paper or report.

      Problems 301–309 deal with the use of NMR spectroscopy for quantitative analysis and for the analysis of mixtures of compounds.

      In Chapter 9, there are also three worked solutions (to problems 117, 146 and 77) as an illustration of a logical approach to solving problems. However, with the exception that we insist that students perform all routine measurements first, we do not recommend a mechanical attitude to problem solving – intuition has an important place in solving structures from spectra as it has elsewhere in chemistry.

      Bona fide instructors may obtain a list of solutions (at no charge) by writing to the authors or EMAIL: [email protected]

      We wish to thank the many graduate students and research associates who, over the years, have supplied us with many of the compounds used in the problems.

       L. D. Field

       H. L. Li

       A. M. Magill

      January 2020