Organic Chemistry I

5.7
Explain that why in step 3 of the above procedure, the answer should be
reversed
to get the final (actual)
configuration?
According to the definition of Fisher projection, the horizontal bond is the bond pointing towards the viewer.
Therefore when the lowest priority group is on a horizontal bond, it is on the position just
opposite
to the way defined by
the Cahn-Ingold-Prelog rule, so the actual configuration should be the reversed version of whatever obtained initially.
5.8
Indicate the configuration of the following compounds.
5.9
Answers to Practice Questions Chapter 5 | 189

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• Draw all stereoisomers for 1-ethyl-3-methylcyclohexane.
• Draw all stereoisomers for 1-ethyl-4-methylcyclohexane.
• Draw all stereoisomers for 1,2-dimethylcyclohexane.
190 | Answers to Practice Questions Chapter 5

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CHAPTER 6 STRUCTURAL IDENTIFICATION OF
ORGANIC COMPOUNDS: IR AND NMR
SPECTROSCOPY
In this chapter we will focus on the methods for chemists to determine the structure of organic compounds. As part of
the efforts for scientists to searching for new compounds for medical, material or new energy resource purpose,
determining the structures of the new compounds is a very critical step. A number of instrumental spectroscopy
techniques have been used broadly for such purpose. Spectroscopy is the study of the interaction of matter and
electromagnetic radiation, and how these interactions can be quantified, analyzed and interpreted to gain information
about the structure of matter. For the purpose to identify the structures of organic compounds, we will specifically
study how molecules interact with electromagnetic radiation, so the spectroscopy techniques in our discussions here
can also be called molecular spectroscopy.
Specifically, we will have discussions about infrared (IR) spectroscopy and nuclear magnetic resonance (NMR)
spectroscopy in this Chapter. IR spectroscopy is a technique applied widely in organic chemistry to detect the
presence or absence of a certain functional group, and NMR spectroscopy is the powerful analytical technique that is
able to determine the bonding arrangement, or the structure, of a molecule.
Chapter 6 Structural Identification of Organic Compounds: IR and
NMR Spectroscopy | 191

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6.1 Electromagnetic Radiation and Molecular
Spectroscopy
Electromagnetic radiation is the radiation composed of oscillating electrical and magnetic fields. The whole
electromagnetic spectrum covers the radiation in very broad range from gamma rays (emitted by the nuclei of certain
radioactive elements), X-rays (used for medical examination of bones), to ultraviolet (UV) light (is responsible for
sunburn, can also be used for dis-infection purpose), microwaves, and radio-frequency waves (used for radio and
television communication, and of the cell phone signal). Visible light, the radiation that is visible to our bare eyes and
what we commonly refer to as “light”, just accounts for a very narrow band out of the full electromagnetic spectrum.
Figure 6.1a The Electromagnetic Spectrum
Electromagnetic radiation exhibits wave-like properties. As a general property of waves, the