Golden rules to nuclear magnetic resonance spectroscopy (NMR) analysis: part 1

academics chemistry organic chemistry
By Madalee

Nuclear magnetic resonance spectroscopy, or NMR, is a fundamental analytical technique used by chemists to determine the structure of organic compounds. Unlike other analytical techniques, such as infrared spectroscopy or mass spectroscopy, NMR allows for the complete interpretation of molecular structure and can be quantitative.

How Does NMR Work?

NMR is based on the principal that certain isotopes of atomic nuclei have an inherent spin state. Chemists are particularly interested in the nuclei 1H, 13C, 19F, and 31P, which all have a spin state of ½.  On its own, a spinning nuclei generates a magnetic field and consequently a magnetic moment (μ). If an external magnetic field (Bo) is applied, the nuclei will either align itself with this magnetic field (lower energy, spin +½) or against it (higher energy, spin -½). When radio waves are applied to the nuclei, those in the lower energy spin state can use the energy from the radio waves to jump up to the higher energy state. The observed result then is either an absorption of energy or a release of energy as the nuclei relaxes back to the lower energy state (spin +½). Depending on the chemical environment of a particular nuclei in a molecule, the effective magnetic field might be “felt” differently, resulting in variations in frequency absorption for each atom in a molecule. Thanks to modern technology, the Fourier Transform method can excite all nuclei in the molecule at once, and a computer can analyze the results and provide a spectrum to the user. 

blog 1-5.png

This seems like a lot of theory and physics…what does this have to do with my orgo class?

Although the theory behind NMR may seem complicated, the actual output (i.e. NMR spectra) can be straightforward to interpret, and most organic chemistry students (YOU) will have to be comfortable using them for structure determination.

What does an NMR spectrum look like?

The output of the frequency absorbances for all the same nuclei can be plotted as a series of peaks called the NMR spectrum. These peaks each have their own multiplicity, or splitting pattern, depending on the neighboring nuclei. The units are in parts per million (ppm), and each peak in the spectrum has a unique chemical shift (δ). The lowest point of the spectrum is traditionally on the right hand side of the spectrum with chemical shifts increasing towards the left (called “downfield”). 1H NMR spectra are usually in the 0-12 ppm range, while 13C NMR spectra are in the 0-200 ppm range. Each functional group in a molecule will have a characteristic chemical shift in the NMR spectrum. These values are useful to know or have access to when trying to interpret an NMR spectrum  (ie table of chemical shifts, and perhaps a sample nmr spectrum). 1H NMR is quantitative, meaning the peaks in the spectrum can be integrated, and this sum will correspond to the number of hydrogens represented by that peak.

It can look like...

blog 3-4.png

blog 4-2.png

Blog 2-1.png

This is the prerequisite information that you'll need to know when reading Part 2 of this guide,, which is how to solve an 1H NMR spectrum. 

Sources Referenced: 

https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/nmr/nmr1.htm

http://www.rsc.org/learn-chemistry/wiki/Introduction_to_NMR_spectroscopy

Comments

topicTopics
academics study skills MCAT medical school admissions SAT expository writing college admissions English MD/PhD admissions strategy writing LSAT GMAT GRE physics chemistry math biology graduate admissions academic advice ACT interview prep law school admissions test anxiety language learning premed MBA admissions career advice personal statements homework help AP exams creative writing MD study schedules computer science test prep Common Application summer activities history mathematics philosophy organic chemistry secondary applications economics supplements research 1L PSAT admissions coaching grammar law psychology statistics & probability legal studies ESL CARS SSAT covid-19 dental admissions logic games reading comprehension engineering USMLE calculus PhD admissions Spanish mentorship parents Latin biochemistry case coaching verbal reasoning DAT English literature STEM excel medical school political science skills AMCAS French Linguistics MBA coursework Tutoring Approaches academic integrity chinese letters of recommendation Anki DO Social Advocacy admissions advice algebra artificial intelligence astrophysics business cell biology classics diversity statement gap year genetics geometry kinematics linear algebra mechanical engineering mental health presentations quantitative reasoning study abroad technical interviews time management work and activities 2L DMD IB exams ISEE MD/PhD programs Sentence Correction adjusting to college algorithms amino acids analysis essay art history athletics business skills careers cold emails data science dental school finance first generation student functions information sessions international students internships logic networking poetry resume revising science social sciences software engineering tech industry trigonometry writer's block 3L AAMC Academic Interest EMT FlexMed Fourier Series Greek Health Professional Shortage Area Italian Lagrange multipliers London MD vs PhD MMI Montessori National Health Service Corps Pythagorean Theorem Python Shakespeare Step 2 TMDSAS Taylor Series Truss Analysis Zoom acids and bases active learning architecture argumentative writing art art and design schools art portfolios bacteriology bibliographies biomedicine brain teaser campus visits cantonese capacitors capital markets central limit theorem centrifugal force chemical engineering chess chromatography class participation climate change clinical experience community service constitutional law consulting cover letters curriculum dementia demonstrated interest dimensional analysis distance learning econometrics electric engineering electricity and magnetism escape velocity evolution executive function freewriting genomics graphing harmonics health policy history of medicine history of science hybrid vehicles hydrophobic effect ideal gas law immunology induction infinite institutional actions integrated reasoning intermolecular forces intern investing investment banking lab reports linear maps mandarin chinese matrices mba medical physics meiosis microeconomics mitosis mnemonics music music theory nervous system neurology neuroscience object-oriented programming office hours operating systems