CHAPTER 13 SPECTROSCOPY ntil the second half of the twentieth century, the structure of a substance-a newly discovered natural product, for example-was determined using information obtained from chemical reactions This information included the identification of functional groups by chemical tests, along with the results of experiments in which the substance was broken down into smaller, more readily identifiable fragments. Typical of his approach is the demonstration of the presence of a double bond in an alkene by cat- alytic hydrogenation and subsequent determination of its location by ozonolysis. After considering all the available chemical evidence, the chemist proposed a candidate struc- ture (or structures) consistent with the observations. Proof of structure was provided either by converting the substance to some already known compound or by an indepen- dent synthesis Qualitative tests and chemical degradation have been supplemented and to a large degree replaced by instrumental methods of structure determination. The most prominent methods and the structural clues they provide are: Nuclear magnetic resonance (NMR)spectroscopy tells us about the carbon skeleton and the of the hydrogens attached to it. Infrared (R) spectroscopy reveals the presence or absence of key functional Ultraviolet-visible (UV-VIs) spectroscopy probes the electron distribution, espe- cially in molecules that have conjugated T electron systems. Mass spectrometry (MS)gives the molecular weight and formula, both of the molecule itself and various structural units within it Back Forward Main MenuToc Study Guide ToC Student o MHHE Website487 CHAPTER 13 SPECTROSCOPY Until the second half of the twentieth century, the structure of a substance—a newly discovered natural product, for example—was determined using information obtained from chemical reactions. This information included the identification of functional groups by chemical tests, along with the results of experiments in which the substance was broken down into smaller, more readily identifiable fragments. Typical of this approach is the demonstration of the presence of a double bond in an alkene by cat￾alytic hydrogenation and subsequent determination of its location by ozonolysis. After considering all the available chemical evidence, the chemist proposed a candidate struc￾ture (or structures) consistent with the observations. Proof of structure was provided either by converting the substance to some already known compound or by an indepen￾dent synthesis. Qualitative tests and chemical degradation have been supplemented and to a large degree replaced by instrumental methods of structure determination. The most prominent methods and the structural clues they provide are: • Nuclear magnetic resonance (NMR) spectroscopy tells us about the carbon skeleton and the environments of the hydrogens attached to it. • Infrared (IR) spectroscopy reveals the presence or absence of key functional groups. • Ultraviolet-visible (UV-VIS) spectroscopy probes the electron distribution, espe￾cially in molecules that have conjugated electron systems. • Mass spectrometry (MS) gives the molecular weight and formula, both of the molecule itself and various structural units within it. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website