Identifying Functional Groups

Bond-line drawings are the preferred drawing style used by practicing organic chemists. In addition to being more efficient, bond-line drawings are also easier to read. As an example, consider the following reaction  

When the reaction is presented in this way, it is somewhat difficult to see what is happening. It takes time to digest the information being presented. However, when we redraw the same reaction using bond-hne structures, it becomes very easy to identify the transformation taking place  

11 Atenolol and enalapril are drugs used In the treatment of heart disease. Both of these drugs lower blood pressure (albeit in different ways) and reduce the risk of heart attack. Using Table 2.1, identify and label all functional groups in these two compounds  

FUNCTIONAL GROUP CLASSIFICATION EXAMPLE CHAPTER FUNCTIONAL GROUP CLASSIFICATION 

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The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

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Identifying Functional Groups and Naming Their Compounds... 

As the molecule vibrates it can also rotate and each vibrational level has associated rotational levels, each of which can be populated. A well-resolved ro - vibrational spectrum can show transitions between the lower ro-vibrational to the upper vibrational level in the laboratory and this can be performed for small molecules astronomically. The problem occurs as the size of the molecule increases and the increasing moment of inertia allows more and more levels to be present within each vibrational band, 3N — 6 vibrational bands in a nonlinear molecule rapidly becomes a big number for even reasonable size molecules and the vibrational bands become only unresolved profiles. Consider the water molecule where N = 3 so that there are three modes of vibration a rather modest number and superficially a tractable problem. Glycine, however, has 10 atoms and so 24 vibrational modes an altogether more challenging problem. Analysis of vibrational spectra is then reduced to identifying functional groups associated... 

The absorption of infrared radiation causes bonds within a molecule to vibrate and infrared spectroscopy can be used to identify functional groups in an organic molecule. 

A number of ex situ spectroscopic techniques, multinuclear NMR, IR, EXAFS, UV-vis, have contributed to rationalise the overall mechanism of the copolymerisation as well as specific aspects related to the nature of the unsaturated monomer (ethene, 1-alkenes, vinyl aromatics, cyclic alkenes, allenes). Valuable information on the initiation, propagation and termination steps has been provided by end-group analysis of the polyketone products, by labelling experiments of the catalyst precursors and solvents either with deuterated compounds or with easily identifiable functional groups, by X-ray diffraction analysis of precursors, model compounds and products, and by kinetic and thermodynamic studies of model reactions. The structure of some catalysis resting states and several catalyst deactivation paths have been traced. There is little doubt, however, that the most spectacular mechanistic breakthroughs have been obtained from in situ spectroscopic studies. 

A13C-NMR spectrum of insoluble organic matter in Murchison showing a prominent peak for aromatic carbon, demonstrating its high abundance. Other, smaller peaks correspond to the various identified functional groups. The small peaks at each end of the spectrum are artifacts of the method. After Cody et al. (2002). 

Some TR absorptions can be attributed to the vibration of individual bonds, and these can be used to identify functional groups present in a molecule. These characteristic group vibrations can be divided into five regions within the IR spectrum ... 

Characteristic stretching and bending frequencies occur in the fingerprint region, but they are less useful for identifying functional groups, because they frequently overlap with other bands. This region is sufficiently complex that a complete analysis of the spectrum is seldom possible. 

As seen above, IR spectroscopy is most commonly used to identify functional groups and bonding patterns in molecules from the higher energy portion of the spectrum (1200-4000 cm ) where absorptions are primarily due to bondstretching vibrations. Some information on atom connectivity in the molecule can also be deduced from the frequency shifts caused by structural factors. In general, however, it is not possible to completely deduce the structure of a molecule by examination of its IR spectrum. However, IR spectroscopy is a powerful complement to NMR spectroscopy for structure determination. 

The fingerprint region of the R spectrum is unique to nearly all compounds, but it is very difficult to read iL You should know about the fingerprint region, but you should use IR to identify functional groups based upon the region from t600 to 3500 cm... 

The primary (1), secondary (2 ), tertiary (3) and quaternary (4) nomenclature is used in a number of situations to define a carbon centre, or to define functional groups like alcohols, halides, amines and amides. Identifying functional groups in this way can be important because the properties and reactivities of these groups vary depending on whether they are primary, secondary, tertiary or quaternary. 

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Coached Tutorial Problem Identifying Functional Groups (page 52)... 

Strengths and Limitations of Infrared Spectroscopy The most useful aspect of infrared spectroscopy is its ability to identify functional groups. IR does not provide much information about the carbon skeleton or the alkyl groups in the compound, however. These aspects of the structure are more easily determined by NMR, as we will see in Chapter 13. Even an expert spectroscopist can rarely determine a structure based only on the IR spectrum. 

Identify functional groups, and draw molecules containing a given functional group. 

The purpose of this problem is to give you experience in calculating the number of double bonds and/or rings in a formula. Additionally, you will learn to draw structures containing various functional groups. Remember that any formula that satisfies the rules of valency is acceptable. Try to identify functional groups in the structures that you draw. 

If we measure the frequencies at which ER energy is absorbed, we can find out the kinds of bonds a compound contains and identify functional groups. 

Identify functional groups by their infrared absorptions. 

IR Spectroscopy. IR spectroscopy is a simple and rapid method of identifying functional groups and skeletal types in milligram samples of solid organic materials. Dispersive spectra have been used to determine the... 

Figure 3.4 The amount ofHMWDOM carbon present within various functional groups in surface and deep (1000 m) ocean waters. Functional groups are identified based on and C-NMR spectroscopy (see text for details) and the quantification uses areas under each NMR resonance. The range of values (shown as error bars) represents direct measurements using the C-NMR spectra and indirect calculations based on H-NMR spectra and converting to carbon based on average C H of identified functional groups. (Data are based on spectra in Figure 3.3 and Benner etal,m2)...

Identify functional groups from a structural formula, and assign names to compounds containing functional groups. 

Spin-spin splitting identifies the number of equivalent protons attached to a carbon atom and is useful in identifying functional groups. 

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