The aim of this textbook is not to provide you, the reader, with large numbers of correlation tables for every form of spectroscopy used by organic chemists; nor is it designed to give you an indepth understanding of the physical processes that occur when molecules interact with electromagnetic radiation. What we hope to do in this textbook is to provide you with a basic understanding of how each type of spectroscopy gives rise to spectra, and how these spectra can be used to determine the structure of organic molecules. This text is aimed at undergraduate students in Years 1 and 2, and is meant to provide an introduction to organic spectroscopic analysis, leading to an appreciation of the information available from each form of spectroscopy and an ability to use spectroscopic information in the identification of organic compounds.
[...]... detail in Chapters 2 4 4 Organic Spectroscopic Analysis Finally, one technique that does not rely upon electromagnetic radiation, mass spectrometry, will be discussed in detail in Chapter 5 I.2 Double Bond Equivalents Before we begin our study of these spectroscopic techniques a reminder of a non -spectroscopic piece of information which is very useful in the determination of organic structures: the... other hand, causes protonation of the amine (Scheme 2.3), and this leads to a loss of the overlap between the amine lone pair and the aromatic n-system The result is a blue or hypsochromic shift (to shorter wavelength) along with a decrease in intensity (Figure 2.6) Scheme 2.3 Effect of pH upon the absorption maxima of an aromatic amine 16 Organic Spectroscopic Analysis Figure 2.6 UV-Vis spectra of aniline... la! cr chromatography (TLC)and HPLC Thin Layer Chromatography TLC is a simple technique that is commonly used for the rapid qualitative analysis of reaction mixtures Many organic compounds used in chemical and pharmaceutical manufacture, and in organic and medicinal chemistry research, contain an aromatic ring or other UV-absorbing system which can be visualized on the TLC plate under a UV lamp Ultraviolet-Visible... transparent in the region of interest Figure 3.1 Nujol IR spectrum (liquid film, NaCl plates) 25 26 Organic Spectroscopic Analysis 32 Selection Rules and HookeysLaw IR spectroscopy corresponds to transitions between the vibrational energy levels of a molecule, involving the stretching or bending of bonds For an organic chemist the region of interest for IR spectroscopy is of wavelength from 2.5 to 15 pm, which... identijication o j the ,functional groups present in the molecule This is the most important use of IR spectroscopy for the organic chemist In looking at these characteristic group vibrations, it is convenient to consider the TR spectrum as being divided into five regions: 27 Organic Spectroscopic Analysis 28 4000-2300 cm-' 2300-1850 cm-' 1850-1500 cm-' 1500-1 000 cm1000-666 cm-' ' Vibrations of single bonds... recently, however, high-performance liquid chromatography (HPLC) has replaced UV analysis in many B.P assays, as most industrial analyses routinely use HPLC Figure 2.8 Ergocalciferol (vitamin D2) and the calculated absorption maximum Figure 2.9 UV-Vis spectrum of ergocalciferol (0.12 mmol dm-" in ethanol) 20 Organic Spectroscopic Analysis In the pharmaceutical industry, medicines are standardized to a particular... moves to higher wavelength 13 14 Organic Spectroscopic Analysis To help us understand how a polar solvent can help to stabilize an excited state, we will consider the 7t + n* transition of an alkene We can represent the ground state and excited state species in a simple way with resonance structures It is important to realize, though, that the dipolar structures in Scheme 2.1 are not the excited state... number of hydrogens which would be present in the fully saturated, acyclic compound with the number actually present, and divide by 2 to give the number of DBEs General Principles NH* 1.2 5 6 Organic Spectroscopic Analysis Ultraviolet-Visible (UV-Vis) Spectroscopy 2 I Instrumentation There are several different types of UV-Vis spectrometers, with the usual instrument met in an undergraduate laboratory... rules can be used to predict the A,, values for a,Punsaturated aldehydes and ketones (enones) and the Amax values for aromatic carbonyl compounds These rules are summarized in Table 2.4 18 Organic Spectroscopic Analysis Table 2.4 UV absorption wavelength correlations for conjugated systems 1 Use the appropriate parent value 215 nm 254 nm (when homocyclic diene -within one ring) Enones Aromatic carbonyls... measure the amount of light passing through the cells There are basic spectrometers that measure the absorbance at a specific wavelength, set by the user, and others that can scan the entire 7 8 Organic Spectroscopic Analysis UV-Vis range Newer spectrometers are usually computer controlled and allow the user greater flexibility, ~ g in overlaying spectra of a reaction mixture over time, 01- constructing . determine the structure of organic molecules. This text is aimed at undergraduate students in Years 1 and 2, and is meant to provide an introduction to organic spectroscopic analysis, leading. Complex Numbers and Linear Algcbra M Cwi(tJtt rind G Doggctt Inorganic Chemistry in Aqueous Solution Organic Spectroscopic Analysis J Biirrctt R J iliirk~eson. D J Reniklf mil P. spectroscopy and an ability to use spectroscopic information in the identification of organic compounds. We will concentrate upon the most commonly used techniques in organic structure determination: