7.S: Summary
- Page ID
- 432218
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)7.1: Chapter Objectives and Preview of Correlation NMR Spectroscopy
- Complex molecules can be hard to elucidate solely with 1-D NMR because it doesn't quite solve the entire picture. This is where correlation NMR spectroscopy can be used.
- The splitting of resonances indicates that groups were "correlated" to each other due to the spins within each group.
- A simple 2-D experiment pulse sequence consists of a relaxation delay, a pulse, a variable time interval (t1), a second pulse, and acquisition (t2).
- In 2-D experiments, the signal detected during acquisition is a function of acquisition time (t2), which has been modulated as a function of the time interval (t1). This means that magnetization evolves around one frequency during t1 and a different frequency during t2.
- The output once Fourier transformed is a 2-D spectrum with two axes.
- One axis (v2) represents the nucleus detected during acquisition (t2), while the other axis (v1) can represent the same nucleus or a different nucleus.
- With two axes, it leads to cross peaks along a diagonal connecting coupled nuclei.
7.3 Two Dimensional Homonuclear NMR Spectroscopy
- Homonuclear 2-D NMR spectroscopy is looking at the correlation of the same nuclei in a molecule.
- COSY looks at 1H coupling to 1H through bonds typically 3 bonds away and relies on the J-coupling to provide spin-spin correlation to indicate which protons are close to each other.
- TOCSY obtains correlations between all protons within a given spin system and begin to chain together fragments of a molecule.
- A molecule can have just one spin system or hundreds in more complex systems.
- The goal in TOCSY is to transfer the magnetization beyond directly coupled spins.
- NOESY determines which signals arise from protons athar are close to each other in space, even if they are not bonded.
7.4 Two Dimensional Heteronuclear NMR Spectroscopy
- Heteronculear 2-D NMR is the correlation between different nuclei, such as a 1H to 13C.
- HSQC is used to determine the proton to carbon or heteroatom (often nitrogen) single bond correlations.
- The purpose of a HSQC is to determine which protons are coupled to what other specific carbon or heteroatom in the molecule through bonds.
- HMBC is used to determine long range 1H to 13C connectivity.
- HMBC gives the correlation between 1H and 13C when separated by two, three, and even four (if through a conjugated system) bonds away.
7.5 Uses of 2-DNMR Spectroscopy
- Complex structure elucidation often requires 2-D NMR spectroscopy.
- HSQC can be used to determine the profile of metabolites in low concentrations (microMolar) accurately.
- TOCSY has been utilized to show changes in tumor cells and identify biomarkers associated with these cells.
- Molecular dynamics can be studied using 2-D NMR spectroscopy to map the molecule's internal mobility patterns.
Skills to Master
- Skill 7.1 Distinguish between 1-D and 2-D techniques.
- Skill 7.2 Learn to read COSY, TOCSY, NOESY, HSQC, HMBC spectra.
- Skill 7.3 Know what type of experiment to use to gain the information needed.
- Skill 7.4 Understand applications of 2-D NMR spectroscopy.
- Skill 7.5 Solve unknown structure determination problems with 2-D spectroscopy.