Book cover for Chemistry

Chemistry

Catherine E. Housecroft, Edwin C. Constable

ISBN #9780273715450

4th Edition

995 Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This section on electronic spectroscopy provides an overview of how molecules absorb ultraviolet and visible light, detailing the concepts of electronic transitions, the importance of the vacuum-UV region, and the role of conjugation in shifting absorption wavelengths. It also emphasizes the impact of solvent choice on spectral outcomes, offering a comprehensive understanding necessary for interpreting spectral data in various practical applications.

Learning Objectives

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Key Concepts

CONCEPT

DEFINITION

Acyclic and cyclic alkanes

A discussion of both open?chain (acyclic) and ring (cyclic) saturated hydrocarbons, emphasizing their structural features, nomenclature, conformational behavior (including ring strain and conformation), and the processes used in their interconversion and synthesis.

Example Problems

Example 1

Electronic spectra are often reported in terms of wavelength but can also be recorded in wavenumbers. Convert the following absorption maxima given in $\mathrm{cm}^{-1}$ into $\lambda$ given in nm: (a) $22700 \mathrm{cm}^{-1} ;$ (b) $35000 \mathrm{cm}^{-1}$

Example 2

Normal laboratory UV-VIS spectrometers operate in the range $\approx 200-900 \mathrm{nm} .$ Which of the following types of electromagnetic radiation does this range cover: (a) visible light; (b) near-UV radiation; (c) vacuum-UV radiation?

Example 3

Do absorptions in the vacuum-UV involve transitions in which $\Delta E$ (change in energy) is greater or smaller than those observed in the visible region?

Example 4

(a) Why are electronic spectra usually characterized by broad absorptions? (b) Absorptions in an electronic spectrum are usually described in terms of $\lambda_{\max }$ and $\varepsilon_{\max }$ values. Draw a diagram of a typical absorption and indicate how you would measure $\lambda_{\max }$ and $\varepsilon_{\max }$ for the absorption. (c) Why is it necessary to quote $\lambda_{\max }$ and $\varepsilon_{\text {max }}$ values rather than $\lambda$ and $\varepsilon ?$

Example 5

For each of the following species, the value of $\lambda_{\max }$ is given. In which part of the UV-VIS range does each species absorb? (a) $\mathrm{I}^{-}, 226 \mathrm{nm} ;$ (b) $\left[\mathrm{C}_{2} \mathrm{O}_{4}\right]^{2-}$ $250 \mathrm{nm} ;(\mathrm{c}) \mathrm{H}_{2} \mathrm{O}, 167 \mathrm{nm} ;(\mathrm{d})(E)-\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{N}=\mathrm{NC}_{6} \mathrm{H}_{5}$ $316 \mathrm{nm} ;(\mathrm{e})\left[\mathrm{Ni}\left(\mathrm{OH}_{2}\right)_{6}\right]^{2+}, 400 \mathrm{nm}$ (one of three bands). (FIGURE CANNOT COPY)
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Step-by-Step Explanations

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Common Mistakes

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