Introduction to Spectroscopy

Citation

Pavia, D. L., Lampman, G. M., Kriz, G. S., & Vyvyan, J. R. (2015). Introduction to Spectroscopy (5th ed.). Cengage Learning.

Chapter Summary

The fifth edition runs to about 780 pages in 11 chapters plus answers to selected problems and 13 appendices of reference data. The publisher presents it as a systematic introduction to spectra and the basic theory of spectroscopic methods that can serve either as the main text of a spectroscopy course or as a companion to an organic chemistry textbook. Its subject is the determination of organic structures from spectra: infrared, mass spectrometry, nuclear magnetic resonance (five chapters) and ultraviolet–visible spectroscopy, ending with combined problems. The chapters close with problems and references, and Chapters 2, 7 and 8 end with sections on how to solve problems of that type.

Chapter 1: Molecular Formulas and What Can Be Learned from Them

A short starting chapter on elemental analysis and the calculations it supports, determination of molecular mass, molecular formulas, the index of hydrogen deficiency, the Rule of Thirteen for generating candidate formulas from a mass, and the nitrogen rule.

Chapter 2: Infrared Spectroscopy

At roughly 90 pages, a complete course in reading IR spectra. After the absorption process, stretching and bending modes, bond properties, dispersive and Fourier-transform spectrometers and sample preparation, the chapter explains what to look for in a spectrum and how to use correlation charts, then surveys the characteristic absorptions of each functional group: hydrocarbons, aromatic rings, alcohols and phenols, ethers, the carbonyl family (aldehydes, ketones, acids, esters, amides, acid chlorides, anhydrides, with the factors that shift the C=O stretch), amines, nitriles and related groups, nitro compounds, salts and amino acids, sulfur and phosphorus compounds and halides. It closes with the background spectrum and a section on solving IR problems.

Chapters 3–4: Mass Spectrometry, Part One: Basic Theory, Instrumentation, and Sampling Techniques; Mass Spectrometry, Part Two: Fragmentation and Structural Analysis

Chapter 3 covers sample introduction, ionization methods (electron ionization, chemical ionization, desorption techniques including MALDI, and electrospray), mass analysers (magnetic sector, double-focusing, quadrupole and time-of-flight), detection, and the determination of molecular weight and molecular formula from precise masses and isotope ratios. Chapter 4 turns to interpretation: the fundamental fragmentation processes (Stevenson's rule, α-cleavage, inductive cleavage, two-bond cleavage, retro-Diels–Alder cleavage and McLafferty rearrangements) and the fragmentation patterns of hydrocarbons, alcohols, phenols and thiols, ethers and sulfides, carbonyl compounds and amines, among other classes. The publisher highlights an introduction to biological molecules in the mass spectrometry coverage.

Chapters 5–6: Nuclear Magnetic Resonance Spectroscopy, Part One: Basic Concepts; Part Two: Carbon-13 Spectra, Including Heteronuclear Coupling with Other Nuclei

The first two of five NMR chapters, titled in the publisher's chapter listing as basic concepts and carbon-13 spectra with heteronuclear coupling. They lay the ground for the coupling analysis of Chapter 7; the publisher singles out the book's modern presentation of one-dimensional NMR.

Chapter 7: Nuclear Magnetic Resonance Spectroscopy, Part Three: Spin–Spin Coupling

A detailed chapter on coupling: one-bond, two-bond, three-bond and long-range coupling constants and their mechanism; magnetic equivalence; diastereotopic hydrogens and methyl groups worked through on specific compounds; tree diagrams for when the n + 1 rule fails; measuring coupling constants from first-order multiplets; second-order spectra (spin-system notation, AB and related systems, simulation, deceptively simple spectra); alkenes, an allylic system, substituted benzene rings and heteroaromatics; coupling of ¹H to ¹⁹F and ³¹P; and a section on solving coupling-constant problems.

Chapter 8: Nuclear Magnetic Resonance Spectroscopy, Part Four: Other Topics in One-Dimensional NMR

Protons on oxygen and nitrogen, exchange and deuterium exchange, tautomerism, quadrupole broadening, amides, solvent effects, chemical shift reagents and chiral resolving agents, determining absolute and relative configuration, and nuclear Overhauser effect difference spectra.

Chapter 9: Nuclear Magnetic Resonance Spectroscopy, Part Five: Advanced NMR Techniques

Pulse sequences, magnetization vectors and pulsed field gradients; the DEPT experiment for counting attached hydrogens; an introduction to two-dimensional methods through COSY, HETCOR (HSQC), inverse detection and NOESY; magnetic resonance imaging; and a full structure problem solved by combining one- and two-dimensional techniques.

Chapter 10: Ultraviolet Spectroscopy

Electronic excitations, band structure, instrumentation, presentation of spectra and solvents; chromophores and the effect of conjugation; the Woodward–Fieser rules for dienes and Woodward's rules for enones; aromatic compounds and their substituent effects; model compound studies; visible spectra and colour; and a practical guide to what to look for in a UV spectrum.

Chapter 11: Combined Structure Problems

Four worked examples are followed by a problem set of about 65 pages and a list of sources of additional problems.

Key Concepts

Chapters 1–2: Formulas and infrared

• Index of hydrogen deficiency: the number of rings and π bonds implied by a molecular formula.
• Rule of Thirteen: a way of generating possible molecular formulas from a molecular mass.
• Correlation charts: tables linking absorption frequencies to functional groups, the main tool for reading IR spectra.

Chapters 3–4: Mass spectrometry

• Ionization methods: electron, chemical, desorption and electrospray ionization, which differ in how much fragmentation they cause.
• Isotope ratios and precise mass: two routes from a mass spectrum to a molecular formula.
• McLafferty rearrangement and α-cleavage: characteristic fragmentation processes used to deduce structure.

Chapters 5–9: NMR

• Coupling constant (J): the splitting between lines of a multiplet, which reflects the bonds connecting coupled nuclei.
• Magnetic equivalence and diastereotopic protons: why chemically similar protons can give different signals.
• Second-order spectra: spectra in which the simple n + 1 rule breaks down because chemical shift differences are small compared with coupling.
• DEPT, COSY and HETCOR: experiments that count attached hydrogens and correlate protons with protons or with carbons.

Chapters 10–11: UV and combined problems

• Chromophore and conjugation: the light-absorbing group and the shift in absorption caused by extended π systems.
• Woodward–Fieser rules: empirical rules for predicting absorption maxima of dienes and enones.
• Combined structure determination: using formula, IR, MS, NMR and UV evidence together to identify an unknown.

Critical Analysis

Strengths

• Built around solving problems. Chapters 2, 7 and 8 end with explicit sections on how to approach problems, Chapter 9 ends with a fully worked combined structure problem, and Chapter 11 provides four worked examples and an extended problem set, with answers to selected problems at the back.
• Depth in NMR. Five chapters take the reader from basic concepts through coupling analysis, second-order spectra, exchange and stereochemical methods to DEPT, two-dimensional techniques and NOESY, more than most introductory treatments.
• Reference value. Thirteen appendices collect IR absorption frequencies, ¹H and ¹³C chemical shift ranges and calculation schemes, coupling constants, solvent shifts, common fragment ions and a guide to mass spectral fragmentation, so the book doubles as a desk reference.
• Long-tested. The publisher notes that the text has been used for more than 30 years; its four authors are chemists at Western Washington University whose stated interests include teaching and, in Vyvyan's case, structure determination by NMR.

Limitations

• Interpretation rather than theory. The physical basis of each method is covered briefly at the start of its chapter; the book does not develop the quantum mechanics of transitions, so it does not substitute for the spectroscopy chapters of a physical chemistry text.
• Organic molecules only. Other spectroscopic methods common in chemistry, such as Raman, fluorescence, atomic and X-ray methods, fall outside its scope.
• Instrumentation of its time. The 2015 edition describes instruments as they stood then, including dispersive IR and magnetic-sector mass analysers alongside FT and time-of-flight instruments; current practice should be checked against newer sources.

Where It Fits in the Course

In a course on quantum chemistry and spectroscopy, Pavia covers the applied side: how to read spectra to determine the structure of organic compounds. The physical basis is in other books on the list. Engel and Reid's Physical Chemistry: Quantum Chemistry and Spectroscopy develops quantum theory and applies it to the main forms of molecular spectroscopy, and Ajit Thakkar's Quantum Chemistry: A Concise Introduction for Students of Physics, Chemistry, Biochemistry and Materials Science explains the concepts behind molecular energy levels for readers who will use spectroscopy rather than develop the theory; either pairs well with Pavia to explain why the spectra look as they do. Donald McQuarrie's Quantum Chemistry and Frank Jensen's Introduction to Computational Chemistry take the theory much further and are not needed for spectral interpretation.

Silverstein, Webster, Kiemle and Bryce's Spectrometric Identification of Organic Compounds is a focused guide to identifying organic structures from mass spectra, infrared data and one- and two-dimensional NMR, built around real-data exercises. It covers much the same ground; with its problem-solving sections and worked combined problems, Pavia suits a first encounter, and Silverstein serves well as a second source of explanation and practice afterwards or alongside.

How to Use This Book

The book suits undergraduates in or after a first organic chemistry course, students taking a dedicated spectroscopy or structure-determination course, and graduate students who need a reference. Familiarity with functional groups and basic structure and bonding is the main prerequisite.

A practical plan:

• Start: Chapter 1 (molecular formulas) and Chapter 2 (IR). The functional-group survey in Chapter 2 can be read selectively, but the sections on what to look for and how to solve IR problems should be read in full.
• NMR core: Chapters 5–7 in order; Chapter 7's sections on diastereotopic protons and second-order spectra are where many students need the most practice.
• Mass spectrometry: Chapters 3–4, with Appendix 12's fragmentation guide alongside.
• Further NMR: Chapter 8 for exchange and stereochemistry, Chapter 9 for DEPT and 2D methods.
• UV: Chapter 10, which can be read at any point after Chapter 1.

Use Chapter 11 throughout rather than only at the end: once IR and NMR are covered, the combined problems are the best practice for real structure determination. Work problems before checking the answers to selected problems, and keep the appendices to hand as quick reference tables.