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Uploaded by station44.cebu on May 19, 2020

Solving Problems with NMR Spectroscopy (2nd Ed.) By Atta-ur-Rahman, Muhammad Iqbal Choudhary and Atia-tul-Wahab

Post author By theSpectroscopy
Post date February 20, 2023
Categories In Books
No Comments on Solving Problems with NMR Spectroscopy (2nd Ed.) By Atta-ur-Rahman, Muhammad Iqbal Choudhary and Atia-tul-Wahab

Free download Solving Problems with NMR Spectroscopy (2nd edition) authored by Atta-ur-Rahman, Muhammad Iqbal Choudhary and Atia-tul-Wahab in pdf.

The second edition of the book Solving Problems with NMR Spectroscopy is aimed to strengthen the understanding of how an NMR spectrometer functions. This revised version of the book takes the same problem-solving approach as the highly praised first edition, published in 1996. The book focuses on describing the basic principles of NMR spectroscopy and explains in detail the functioning of an NMR spectrometer.

The optimum use of this powerful technique is introduced step by step, and common problems encountered by the practitioners and users of NMR spectroscopy are described in an easy-to-understand manner. The real strength of the book is its highly practical approach in describing both the concepts and applications of NMR spectroscopy.

The second edition introduces a number of new topics, including developments in NMR hardware, such as cryogenically cooled probes, new probeheads, high-field magnets, and DNP–NMR, as well as innovative pulse sequences, such as DOSY, concatenated NMR techniques, and PANSY.

Particularly interesting is a new chapter on sensitivity issues in NMR spectroscopy and their currently available applications, which have driven most of the developments in this field. Another chapter on recent developments in NMR spectroscopy updates the readers about the changing landscape in this field.

Over 180 penetrating problems and their well-described solutions help to reinforce and test the understanding of the readers about various aspects of modern NMR spectroscopy. Many of these problems focus on developing the interpretation skills of the readers in various types of NMR spectra toward structure determination.

The Basics of Modern NMR Spectroscopy
Creating NMR Signals
Sensitivity Enhancement
Spin-Echo and Polarization Transfer
The Second Dimension
Nuclear Overhauser Effect
Important 2D NMR Experiments
Playing with Dimensions in NMR Spectroscopy
Some Key Developments in NMR Spectroscopy
Logical Approach for Solving Structural Problems

Free download Solving Problems with NMR Spectroscopy (2nd edition) authored by Atta-ur-Rahman, Muhammad Iqbal Choudhary and Atia-tul-Wahab in pdf from following download link(s).

Sometime download link(s) is/are not visible on mobile devices, so if you face this issue, kindly do visit this page via laptop/desktop computer.

Password for Download Links: thespectroscopy.com

File Size: 49.1 MB | Pages: 521 | Download Instructions | Disclaimer

Organic Spectroscopy

Chem 203 Professor James S. Nowick

Problems from Previous Years' Exams

This archive includes six types of problems from the midterm and final exams of my Chem 203 Organic Spectroscopy class. The first three focus on infrared spectroscopy , mass spectrometry , and 1D NMR spectroscopy . The next focuses on using these three techniques together to determine the structures of organic compounds . The last two categories incorporate 2D NMR spectroscopy and are thus considered "advanced." The advanced spectral analysis problems focusing on analyzing 1- and 2D NMR spectra to address questions of stereochemistry. The advanced structure determination problems focus on using all of these techniques to determine the structures of organic compounds.

INFRARED (IR) SPECTROSCOPY PROBLEMS

2014 Midterm Exam Part I.1. ( 2014-MT-I.1.pdf ) Problem Type: Match aromatic compounds with IR spectra. Techniques: IR spectroscopy . Notes: A set of compounds with unusual functional groups. One of my favorites.

2013 Midterm Exam Part I.1. ( 2013-MT-I.1.pdf ) Problem Type: Match aromatic compounds with IR spectra. Techniques: IR spectroscopy . Notes: A set of aromatic compounds with similar structures but different functional groups.

2012 Midterm Exam Part I.1. ( 2012-MT-I.1.pdf ) Problem Type: Match aromatic compounds with IR spectra. Techniques: IR spectroscopy . Notes: A set of aromatic compounds with carbonyl and other functional groups.

2011 (fall) Midterm Exam Part I.1. ( 2011f-MT-I.1.pdf ) Problem Type: Match aromatic compounds with IR spectra. Techniques: IR spectroscopy . Notes: A set of aromatic compounds bearing different functional groups.

MASS SPECTROMETRY (MS) PROBLEMS

2014 Midterm Exam Part I.2. ( 2014-MT-I.2.pdf ) Problem Type: Interpret peaks of a large molecule, maitotoxin, in negative and positive ion modes Techniques: Negative ion FAB and ESI mass spectrometry . Notes: Concepts in mass, charge, and isotopomers. One of my favorites

2013 Midterm Exam Part I.2. ( 2013-MT-I.2.pdf ) Problem Type: Interpret peaks in an ESI mass spectrum. Techniques: ESI mass spectrometry . Notes: This is modern ESI MS problem that focuses on the concepts of mass, charge, and molecular formula.

2012 Midterm Exam Part I.2. ( 2012-MT-I.2.pdf ) Problem Type: Interpret peaks in EI and ESI mass spectra. Techniques: EI and ESI mass spectrometry . Notes: Concepts in fragmentation, isotope patterns, and molecular ions.

2011 (fall) Midterm Exam Part I.3. ( 2011f-MT-I.3.pdf ) Problem Type: Identify the transition metal complex from the isotope pattern. Techniques: EI mass spectrometry . Notes: Electron ionization (EI) mass spectra are shown for five transition metal acetylacetonate (acac) complexes.

NUCLEAR MAGNETIC RESONANCE (NMR) SPECTROSCOPY PROBLEMS

2014 Midterm Exam Part I.3. ( 2014-MT-I.3.pdf ) Problem Type: Interpret the 1 H NMR spectrum of ( S )-glycidyl benzyl ether. Techniques: 1 H NMR spectroscopy . Notes: This problem gets to the heart of coupling and diastereotopicity. It is one of my all-time favorites.

2013 Midterm Exam Part I.3. ( 2013-MT-I.3.pdf ) Problem Type: Match regioisomeric aromatic compounds with 1 H NMR spectra. Techniques: 1 H NMR spectroscopy . Notes: This is a great little matching problem that gets to the heart of pattern recognition, coupling, and symmetry in 1 H NMR spectroscopy.

2013 Midterm Exam Part I.4. ( 2013-MT-I.4.pdf ) Problem Type: Stereochemical determination by 1 H NMR spectroscopy. Techniques: 1 H NMR spectroscopy . Notes: This problem builds on some of my favorite concepts in sterochemical determination in a cyclohexane ring system (2-phenyl-1-cyclohexanol) from the coupling pattern.

2012 Midterm Exam Part I.3. ( 2012-MT-I.3.pdf ) Problem Type: Match the eight constitutional isomeric alcohols C 5 H 12 O with 1 H NMR and 13 C NMR spectra. Techniques: 1 H NMR and 13 C NMR spectroscopy . Notes: A challenging matching problem that probes concepts of chemical equivalence and symmetry in 1 H NMR spectroscopy. One of my favorites.

2011 (fall) Midterm Exam Part I.2a. ( 2011f-MT-I.2a.pdf ) Problem Type: Match the regioisomers of dinitrophenol with 1 H NMR spectra. Techniques: 1 H NMR and 13 C NMR spectroscopy . Notes: A matching problem that probes concepts of chemical equivalence and symmetry in 1 H NMR spectroscopy.

2011 (fall) Midterm Exam Part I.2b. ( 2011f-MT-I.2b.pdf ) Problem Type: Match the regioisomers of methylpyridine with 1 H NMR spectra. Techniques: 1 H NMR and 13 C NMR spectroscopy . Notes: A matching problem that probes concepts of chemical equivalence and symmetry in 1 H NMR spectroscopy.

BASIC STRUCTURE DETERMINATION PROBLEMS

2014 Midterm Exam Part II.1. ( 2014-MT-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS; IR (thin film on NaCl plates); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: A small but challenging molecule. One of my favorites.

2014 Midterm Exam Part II.2. ( 2014-MT-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS; IR (thin film on NaCl plates); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: This problem was designed to build on concepts of 1 H NMR non-first-order coupling pattern recogntion and symmetry.

2014 Midterm Exam Part II.3. ( 2014-MT-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS; IR (thin film on NaCl plates); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: A simple but challenging molecule with a rich 1 H NMR spectrum.

2014 Midterm Exam Part II.4. ( 2014-MT-II.4.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS; IR (KBr pellet); 500 MHz 1 H NMR in CD 3 SOCD 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CD 3 SOCD 3 . Notes: This problem was designed to build on concepts of 1 H NMR coupling pattern recogntion and symmetry.

2013 Midterm Exam Part II.1. ( 2013-MT-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; CI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in C 6 D 6 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in C 6 D 6 . Notes: We designed this molecule to illustrate principles of coupling patterns in the 1 H NMR spectrum and isotope patterns in the mass spectrum.

2013 Midterm Exam Part II.2. ( 2013-MT-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS and CI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in C 6 D 6 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in C 6 D 6 .

2013 Midterm Exam Part II.3. ( 2013-MT-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in C 6 D 6 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in C 6 D 6 . Notes: A pretty spectrum with interesting coupling patterns. One of my favorites.

2013 Midterm Exam Part II.4. ( 2013-MT-II.4.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: A small but challenging molecule. One of my favorites.

2012 Midterm Exam Part II.1. ( 2012-MT-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; EI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: Concepts in pattern recognition, symmetry, and diastereotopicity.

2012 Midterm Exam Part II.2. ( 2012-MT-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; EI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in CD 3 SOCD 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CD 3 SOCD 3 . Notes: We designed this molecule to illustrate principles of coupling patterns in the 1 H NMR spectrum and isotope patterns in the mass spectrum.

2012 Midterm Exam Part II.3. ( 2012-MT-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; EI-MS (low resolution/accuracy); IR (solution in CHCl 3 in a 0.1 mm CaF 2 cell); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: A small but challenging molecule.

2012 Midterm Exam Part II.4. ( 2012-MT-II.4.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; EI-MS (low resolution/accuracy); IR (thin film on NaCl plates); 500 MHz 1 H NMR in CDCl 3 ; 125.8 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: Concepts in pattern recognition, symmetry, and diastereotopicity.

2011 (fall) Midterm Exam Part II.1. ( 2011f-MT-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; EI-MS (low resolution/accuracy); IR (thin film on salt plates); 500 MHz 1 H NMR in CDCl 3 ; 125.6 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: Concepts in pattern recognition and spin-spin coupling.

2011 (fall) Midterm Exam Part II.2. ( 2011f-MT-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: Exact mass; ESI-MS (low resolution/accuracy); IR (solution in CH 2 Cl 2 in a 0.1 mm CaF 2 cell); 400 MHz 1 H NMR in CDCl 3 ; 100.6 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: Concepts in pattern recognition and spin-spin coupling.

2011 (fall) Midterm Exam Part II.3. ( 2011f-MT-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Techniques: EI-MS (low resolution/accuracy); IR (thin film on salt plates); 500 MHz 1 H NMR in CDCl 3 ; 125.6 MHz 13 C NMR, DEPT 90, and DEPT 135 in CDCl 3 . Notes: A small molecule with interesting IR and NMR spectra.

ADVANCED SPECTRAL ANALYSIS PROBLEMS

2014 Final Exam Part I. ( 2014-F-I.pdf ) Problem Type: Assignment of NMR resonances and stereochemical analysis. Compound Information: Two diastereomeric L-hexopyranose pentaacetates. Techniques: 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT, COSY, HMQC, NOESY, and a 1D NOE experiment . Notes: This problem focuses on conformational and stereochemical analysis in two diastereomeric L-hexopyranose pentaacetates.

2013 Final Exam Part I. ( 2013-F-I.pdf ) Problem Type: Assignment of NMR resonances and stereochemical analysis. Compound Information: A pentacyclic compound. Techniques: 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT, COSY, TOCSY (20 ms mixing time), HMQC, HMBC, NOESY, and HSQC-TOCSY spectra with 5-, 10-, 25-, and 50-ms mixing times . Notes: This problem focuses on conformational and stereochemical analysis in a system of fused cyclohexane rings.

2012 Final Exam Part I. ( 2012-F-I.pdf ) Problem Type: Assignment of NMR resonances and stereochemical analysis. Compound Information: A tricyclic compound. Techniques: 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT, COSY, TOCSY, HMQC, HMBC, NOESY, and HSQC-TOCSY spectra with 5-, 10-, 20-, and 100-ms mixing times . Notes: This problem focuses on conformational and stereochemical analysis in a fused 5,6 ring system. It is a great showcase for HSQC-TOCSY, which helps tremendously in assignment of the resonances.

2011 (fall) Final Exam Part I. ( 2011-F-I.pdf ) Problem Type: Assignment of NMR resonances and stereochemical analysis. Compound Information: A tricyclic compound. Techniques: 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT, COSY, TOCSY, HMQC, HMBC, NOESY, and HSQC-TOCSY spectra with 5-, 10-, 20-, and 100-ms mixing times. . Notes: This problem focuses on conformational and stereochemical analysis in a fused 5,6 ring system. It is a great showcase for HSQC-TOCSY, which helps tremendously in assignment of the resonances.

ADVANCED STRUCTURE DETERMINATION PROBLEMS

2014 Final Exam Part II.1. ( 2014-F-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 10 H 17 NO 2 . Techniques: IR (thin film from CHCl 3 on salt plates), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, TOCSY (100 ms mixing time), HMQC, HMBC, and NOESY, and a 1D NOE experiment . Notes: This problem proved surprisingly challenging in spite of the small size of the molecule. It was the most popular problem of the 2014 final exam Part II problems.

2014 Final Exam Part II.2. ( 2014-F-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 18 H 21 NO 4 . Techniques: IR (KBr pellet), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, TOCSY (60 ms mixing time), HMQC, HMBC, NOESY, and HSQC-TOCSY spectra with increasing mixing times (5, 10, 25, and 50 ms) . Notes: This was the hardest and least popular of the 2014 final exam Part II problems. It is an beautiful and complex molecule with a disperse 1 H NMR spectrum with interesting resonances.

2014 Final Exam Part II.3. ( 2014-F-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 17 H 22 O 3 . Techniques: IR (KBr pellet), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, TOCSY (150 ms mixing time), HMQC, HMBC, NOESY, and select regions of the HSQC-TOCSY spectra with increasing mixing times (5, 10, 25, and 50 ms) . Notes: This problem was the second most popular of the 2014 final exam Part II problems. There is moderate overlap of the 1 H NMR resonances. The TOCSY and 50-ms HSQC-TOCSY spectra nicely illuminate the major spin systems.

2013 Final Exam Part II.1. ( 2013-F-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 18 H 25 NO. Related to codeine. Techniques: IR (solution in CHCl 3 ), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY (150 ms mixing time) and NOESY . Notes: The easiest of the 2013 final exam Part II problems. It is also my favorite. Although the molecule is large the problem is very workable and satisfying. I had been wanting to introduce it for a number of years, but it was only in 2013 that we were able implement it.

2013 Final Exam Part II.2. ( 2013-F-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 16 H 25 NO 2 . Related to codeine. Techniques: IR (solution in CHCl 3 ), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY (150 ms mixing time) and NOESY. Also included are select regions of the HSQC-TOCSY spectra with increasing mixing times . Notes: The hardest and least popular of the 2013 final exam Part II problems.

2013 Final Exam Part II.3. ( 2013-F-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 16 H 24 O. Techniques: IR (solution in CHCl 3 ), 500 MHz 1 H NMR, 125.8 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, TOCSY (20 ms mixing time), HMQC, HMBC, 1D NOE (irradiation at 3.36 ppm), and NOESY . Notes: This problem was the most popular of the 2013 final exam Part II problems.

2012 Final Exam Part II.1. ( 2012-F-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 17 H 19 ClO. Techniques: IR (solution in CHCl 3 ), 600 MHz 1 H NMR, 150.9 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY and NOESY . Notes: This was the second most popular of the 2012 final exam Part II problems. In spite of the larger size of the molecule (compared to the other two problems) it is manageable.

2012 Final Exam Part II.2. ( 2012-F-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 9 H 10 O 4 . Techniques: IR (thin film from CHCl 3 solution on NaCl plates), 500 MHz 1 H NMR, 125.7 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY and NOESY . Notes: The hardest and least popular of the 2012 final exam Part II problems. Although the molecule is small, it is challenging.

2012 Final Exam Part II.3. ( 2012-F-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 10 H 19 N. Techniques: IR (thin film on NaCl plates), 500 MHz 1 H NMR, 125.7 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY and NOESY . Notes: This was the most popular of the 2012 final exam Part II problems. In spite of the small size of the molecule, its structure is actually quite challenging, in part due to W-coupling seen in the COSY.

2011 (fall) Final Exam Part II.1. ( 2011f-F-II.1.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 15 H 22 O 2 . Techniques: IR (Thin Film on NaCl), 500 MHz 1 H NMR, 125.7 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY and NOESY . Notes: This was the easiest and most popular of the 2011 fall final exam Part II problems.

2011 (fall) Final Exam Part II.2. ( 2011f-F-II.2.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 16 H 22 O. Techniques: IR (Thin film on NaCl), 400 and 500 MHz 1 H NMR, 125.7 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY, and NOESY . Notes: This was my favorite among the 2011 fall final exam Part II problems.

2011 (fall) Final Exam Part II.3. ( 2011f-F-II.3.pdf ) Problem Type: Structure determination and assignment of NMR resonances. Compound Information: Molecular formula C 10 H 16 O. Techniques: IR (Thin Film on NaCl), 500 MHz 1 H NMR, 125.7 MHz 13 C NMR, DEPT-90, DEPT-135, COSY, HMQC, HMBC, TOCSY, and NOESY . Notes: In spite of the small size of this molecule, it was the hardest and most frustrating of the 2011 fall final exam Part II problems Only a few of those who attempted it got the correct structure and stereochemistry.

Chemistry Steps

Organic Chemistry

Organic structure determination, nmr practice problems .

In the following examples, we will learn how to solve NMR practice problems step-by-step in over 100 min video solutions which is essential for organic structure determination.

The emphasis is on the 1 H proton NMR and most problems are based on understanding its key principles such as the number of NMR signals , integration , signal splitting (multiplicity) , and, of course, the strategies of putting all of these together to come up with the correct structure.

Aside from the 1 H NMR , we will also go over determining the hydrogen deficiency index (HDI), solving problems where the 13 C NMR, DEPT , and IR are given along with the 1 H NMR spectrum.

The problems are chosen to demonstrate the most common patterns in 1 H NMR spectroscopy , as well as, the situations where you need to consider the possibility of signal overlapping , incorrect absolute values of integrations , as the instrument measures only the relative area for each peak, examples where fairly large molecules give rise to spectra with few signals because of the symmetry elements . We will also discuss the purpose of shaking the sample with deuterated solvents.

How to determine the structure of an unknown compound using NMR spectroscopy

Two things you will need to do very often:

IR – It will be very beneficial for you to remember key signals in IR spectroscopy so that you can identify the functional groups. Solving IR problems – here .

Before you start working on the first problem or getting stuck on one, let’s go ahead and summarize the most common patterns that you need to recognize.

Common Splitting Patterns in NMR spectroscopy

Start by analyzing the aliphatic region. Many molecules have at least one methyl group and depending on its environment, common splitting patterns are observed.

A triplet with an integration of three represents a methyl with an adjacent CH 2 group. So, look for a triplet and a quartet with integrations 3 and 2 which indicates an ethyl group ( Figure 1 a ).

If there is a singlet with an integration of 3, this represents an isolated methyl group ( b ) . On the other hand, if the singlet integrates to 9 protons, this indicates a tert-Butyl group ( c )

Another common fragment is the combination of a doublet (6H) and a septet ( d ) . This indicates an isopropyl group where the methyl protons are split into a doublet by one adjacent proton and the six equivalent protons of the methyl groups split the signal of that one proton into a septet.

If you see a bunch of triplets each integrating to two protons, think about the -CH 2 -CH 2 – ethylene group ( e ) .

Other Regions and Splitting Patterns

Alkene protons appear at ~5-6 ppm and you can recognize them by the small integration (1 or 2) and complex splitting. This is because all the protons on a double bond are capable of splitting each other and the coupling constants vary anywhere from 5-18 Hz.

Aromatic protons appear at the ~7-8 ppm region. If you have a signal there, the first thing is to check how many groups (or how many protons) are on the aromatic ring. And this is done simply by looking at the integration:

One common splitting pattern in the aromatic region is the presence of two doublets each integrating to two protons. This indicates a symmetrically substituted ring with two groups (1, 4- or para – substituted).

Most other substitution patterns give complex splitting and the easiest for you will be looking at the total integration of all the aromatic signals.

Next functional group recognizable in 1 H NMR spectroscopy is the ~10 ppm signal of aldehydes. Usually, it shows up as a singlet, though splitting with adjacent protons is not uncommon either:

Another way of identifying aldehydes and ketones as well as checking for a ~200 ppm signal on the 13 C NMR. Esters and carboxylic acids appear less downfield – 160-180 ppm.

The OH peak

Like for the IR spectroscopy, the OH peak is a good indicator here as well. Look for a broad peak anywhere from 1-6 ppm. Most often though it will be in the 4-6 range.

Remember also that the OH signal is not split by adjacent protons unless the sample is very dry.

Other groups that give broad, and sometimes, deuterium-exchangeable signals are the amines, amides, and thiols.

Carboxylic acids

If you see a broad signal at 12 ppm, 90% of the time it tells you about a carboxylic acid.

In the following NMR practice problems, we will go over the best strategies you can use for identifying the structure of unknown compounds. As a Chemistry Steps Prime member, you will also get access to the Spectroscopy Summary Sheets in addition to these over 100 min videos of solving NMR problems.

NMR and IR Spectroscopy Summary Sheets

1. How to Solve IR Problems in 3 steps!

2. NMR Spectroscopy – 5 pages that include

Chemical Shift and Integration
Number of NMR signals
Spin-Spin Splitting
13 C NMR Spectroscopy
Determining the Structure of an Unknown

The 1 H NMR spectrum of compound X ( C 4 H 8 O 2 ) is shown below. It also shows a strong IR absorption band near 1730 cm −1 . Propose a structure for X .

This content is for registered users only.

Click here to Register!

By joining Chemistry Steps, you will gain instant access to the answers and solutions for all the Practice Problems including over 20 hours of problem-solving videos, Multiple-Choice Quizzes, Puzzles, and t he powerful set of Organic Chemistry 1 and 2 Summary Study Guides .

The 1 H NMR spectrum of compound X ( C 2 H 3 Cl 3 ) is shown below. Propose a structure for X.

The 1 H NMR spectrum of compound X ( C 2 H 4 Cl 2 ) is shown below. Propose a structure for X.

The 1 H NMR and 13 C spectra of compound X ( C 5 H 10 Cl 2 ) are shown below. Propose a structure for X.

The 1 H NMR and 13 C spectra of compound X (C 6 H 12 O 2 ) are shown below. Propose a structure for X .

The 1 H NMR and 13 C spectra of compound X ( C 10 H 12 O 2 ) are shown below. The 13 C DEPT techniques were also used to identify the carbon types. Propose a structure for X.

The 1 H NMR of compound X ( C 9 H 10 O 2 ) is shown below. Propose a structure for X.

The 1 H NMR and 13 C spectra of compound X ( C 5 H 10 O 2 ) are shown below. Propose a structure for X.

The 1 H NMR and 13 C spectra of compound X ( C 4 H 6 O 2 ) are shown below. Propose a structure for X.

The 1 H NMR of compound X ( C 5 H 8 O 2 ) are shown below. Propose a structure for X.

The 1 H NMR of compound X ( C 5 H 10 O 2 ) are shown below. Propose a structure for X.

The 1 H NMR of compound X ( C 9 H 12 O ) are shown below. When the sample is mixed and shaken with an excess of deuterium oxide, the signal at 6 ppm disappears. Propose a structure for X.

The 1 H NMR of compound X ( C 7 H 14 O ) are shown below. Propose a structure for X.

The 1 H NMR and 13 C spectra of compound X ( C 8 H 10 O ) together with its IR spectrum are shown below. Propose a structure for X.

The 1 H NMR of compound X ( C 4 H 9 Br ) are shown below. Propose a structure for X.

The 1 H NMR spectra of three isomers of Butanol are shown below. Draw the structures of all the isomers for butanol and assign each spectrum to the correct isomer.

NMR spectroscopy – An Easy Introduction
NMR Chemical Shift
NMR Chemical Shift Range and Value Table
NMR Number of Signals and Equivalent Protons
Homotopic Enantiotopic Diastereotopic and Heterotopic
Homotopic Enantiotopic Diastereotopic Practice Problems
Integration in NMR Spectroscopy
Splitting and Multiplicity (N+1 rule) in NMR Spectroscopy
NMR Signal Splitting N+1 Rule Multiplicity Practice Problems
13 C NMR NMR
DEPT NMR: Signals and Problem Solving
NMR Spectroscopy-Carbon-Dept-IR Practice Problems

6 thoughts on “NMR Practice Problems – Solving Strategies”

Thank you! These strategies are great and I feel more optimistic about NMR questions. Hopefully I won’t get them though… : )

I hope you got the NMR right on the test.

Super helpful for understanding NMR. Thank you!

Great to hear, Pokharel.

This was great! Thank you

You are welcome, Andrew.

Guide to Solving NMR Questions

How to solve any nmr question.

Solving NMR questions is easier than you think. All you need is a step-by-step process to help guide you through each question. And here it is…

Most NMR questions on an exam involve determining a specific structure rather than memorizing and repeating various NMR values. Typically, you will be given an NMR spectra and a molecular formula (sometimes an IR spectra will be provided). I have put together a few ideas that might make this process a bit easier. I am in the process of putting together a more concise document than this as a study aid. This post is meant to walk you through the thought process of how to tackle this type of problem. The description is a bit long (….so hold on!), but once you get it, you can just use the algorithm to solve your NMR problems. Here are some reference values and a couple of proton NMR spectra:

Proton NMR Reference Values

(cem.msu.edu)

(process-nmr.com)

(Our example 1H NMR spectra for this post; unknown source)

Start with an algorithm to get you on track

When staring an NMR question, you can use the following algorithm to help guide you through the thought process:

(above should say C2H5Cl = C2H6)

Calculate Degrees of Freedom

We notice the first thing says calculate degrees of unsaturation… what is that ? This allows us to determine if there are any double bonds or rings (cyclic structures) in the compound. Let’s look at an example; the formula is C 4 H 8 O 2 . Now, we need to compare this formula with the formula of a completely saturated hydrocarbon (all single bonds…no double bonds):

This formula tells us how many hydrogens we need to have a carbon compound with NO double bonds or rings. Let’s look at our example…

If I have a compound with 4 carbons, this 4 refers to n. Now, if we plug this in the formula, we get

C 4 H 2(4)+2 = C 4 H 10

This says that if we have a compound with only 4 carbons, we need 10 hydrogens to have a compound with no double bonds or rings. If we look at our example, we have C 4 H 8 O 2 . For now, all we need to look at is the C 4 H 8 when dealing with degrees of unsaturation (we will discuss what to do with heteroatoms a bit later). What we now want to do is subtract the hydrogens in our example ( C 4 H 8 ) from the saturated formula ( C 4 H 10 ):

C 4 H 10 – C 4 H 8 = 2 hydrogens

This leaves us with a value of 2. Now, the last things we do to get our degrees of unsaturation is divide this number by 2:

How to use the degrees of unsaturation to get the answer

This leaves us with 1; therefore, we have 1° of unsaturation. So, what does this mean? Each degree of unsaturation equates to a double bond or ring. Here are a few examples to further clarify:

1° of unsaturation = 1 double bond or 1 cyclic structure

2° of unsaturation = 2 double bonds; 1 alkyne; 1 double bond and 1 cyclic structure; 2 cyclic structures

3° of unsaturation = 3 double bonds; 2 double bonds and 1 cyclic structure; etc…

When you see 4° of unsaturation, think benzene; 3° of unsaturation for the 3 double bonds and 1° of unsaturation for the ring.

In our example, it means we have one double bond or one cyclic structure in our compound. Let’s look at few ring systems:

The larger the ring, the more stable the ring (with this series). Three and four-membered rings are rare. Usually, you will hear more about 5- and 6-membered rings. Since this is the case, we more than likely have a double bond (but never rule out a ring until you have looked at the NMR spectra).

Next, if we look at the algorithm, we need to consider the other atoms (other than carbon and hydrogen) in our formula…oxygen. Since we have degrees of freedom…think carbonyl. That is all we can do for now with our algorithm. Let’s now look at our spectra and see if we can start to determine the structure from the peaks:

Interpreting the spectra – splitting patterns

We have three peaks: a quartet around 4 ppm; a singlet around 2 ppm; and a triplet around 1 ppm. At this point, let’s review singlet, doublet, triplet, quartet, and multiplet:

What do these peaks refer to and how to we get the specific peak pattern? Well, we use the n+1 rule to figure out the pattern:

Putting the fragments together

Once you have your fragments, it is a matter of figuring out how to put them together. By looking at the spectra and where the peaks show up (ppm), you can figure out how the fragments go together.

Click NMR pictures to see the images as a PDF.

Don’t forget IR Spectroscopy!

Here is a simple guide showing you the most common IR values

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7.7: 2-D NMR Problems

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Learning Objectives

Solve unknown problems using a variety of spectra and the molecular formula.

Exercise \(\PageIndex{1}\)

Propose a structure using the spectral data below for C 10 H 14 O. Note: You may need to check for solvent peaks. This sample was dissolved in CDCl 3 .

COSY:

NOESY:

13 C:

HSQC:

HMBC:

Exercise \(\PageIndex{2}\)

Present an analysis of the following data and propose a structure.

MW: 131 amu

The full 1 H NMR spectrum in D 2 O:

An expansion:

Example \(\PageIndex{3}\)