Texas Lutheran University 1 H NMR Interpretation: A New Tool for Students John V. McClusky Texas Lutheran University

Why Teach NMR Interpretation? Necessary for molecular identification Important for teaching problem solving skills –Complex and abstract –Must concentrate on details and big picture –“You guess, you loose”

Texas Lutheran University The Process Students must use –Integration Number of hydrogens making the peak –Multiplicity Number of adjacent hydrogens –Chemical shift Functional groups Determine the molecular structure

Texas Lutheran University The Problem Doesn’t look like

Texas Lutheran University Typical Student Errors Ignore integration, multiplicity, or chemical shift Interpret peak incorrectly –n+1 or n-1? –Switch integration and multiplicity Force spectrum to “match” preconceived molecule

Texas Lutheran University NMR Mosaic Goals Make NMR Interpretation more concrete Reinforce need to use all data –Chemical shift –Multiplicity –Integration Visualize relationship between multiplicity and connectivity Retain all problem-solving aspects

Texas Lutheran University NMR Mosaic Spectral peaks Molecular fragments Molecule fit mismatch Finished Revise --

Texas Lutheran University Advantages of the NMR Mosaic Requires use of integration, chemical shift, and multiplicity Accentuates student’s interpretation errors Eases interpretation of complex multiplets Illustrates relationship between connectivity and multiplicity Helps students understand and visualize NMR interpretation

Texas Lutheran University Mosaic Pieces H | ─C─ | H CH 3 Funct. Grp. CH 3 Funct. Grp ++= H | ─C─ | H Peak is from Splitting indicates Chemical shift Final mosaic piece a CH 2 adjacent CH 3 indicates adjacent functional group Students add static clings to generic pieces to produce a custom piece encoding connectivity and functionality

Texas Lutheran University Example: C 3 H 7 Cl

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H CH 2

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H CH 2 Funct. Grp.

Texas Lutheran University Example: C 3 H 7 Cl X- H | ─C─ | H CH 2 Funct. Grp.

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H CH 2 Funct. Grp. X- H | ─C─ | H CH 2 CH 3

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H CH 2 Funct. Grp. X- H | ─C─ | H CH 2 CH 3 H | H─C─ | H CH 2

Texas Lutheran University Example: C 3 H 7 Cl H | ─C─ | H CH 2 Funct. Grp. X- H | ─C─ | H CH 2 CH 3 H | H─C─ | H CH 2 1-chloropropane

Texas Lutheran University NMR Mosaic Simplifies Interpretation of Complex Multiplets Adjoining pieces specify connectivity Interpretation is no longer “impossible”

Texas Lutheran University Example: C 4 H 9 Cl

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2 H | ─C─ | H Undetermined Splitting

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2 H | ─C─ | H Undetermined Splitting H | H─C─ | H CH

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2 H | ─C─ | H Undetermined Splitting H | H─C─ | H CH H | H─C─ | H CH 2

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2 H | ─C─ | H Undetermined Splitting H | H─C─ | H CH H | H─C─ | H CH 2

Texas Lutheran University Example: C 4 H 9 Cl X- H | ─C─ | Funct. Grp. CH 3 CH 2 H | H─C─ | H CH H | H─C─ | H CH 2 H | ─C─ | H CH CH 3 2-chlorobutane

Texas Lutheran University NMR Mosaic Helps Students Catch Mistakes Mosaic pieces no longer match Focus students on incorrectly interpreted peaks

Texas Lutheran University Example: C 3 H 7 Cl

Texas Lutheran University Example: C 3 H 7 Cl H | H─C─ | H CH 2 H | ─C─ | H CH 3 H | ─C─ | H CH 2 Funct. Grp. X- Incorrect Match ↑

Texas Lutheran University Example: C 3 H 7 Cl H | H─C─ | H CH 2 H | ─C─ | H CH 2 Funct. Grp. X- Corrected Piece Matches H | ─C─ | H CH 2 CH 3

Texas Lutheran University Functional Groups Easily used for spectra with over 10 carbons plus aromatic rings All major functional groups including: – Aromatic rings (mono and di-substituted) – Alcohols, ethers, esters, aldehydes, ketones, carboxylic acids, amines …… – Alkenes

Texas Lutheran University Student Experiences Students found the NMR Mosaic a great aid in NMR Interpretation Much higher percentage of students successfully solved problems Allows much more realistic problems on exams Better students weaned themselves off NMR Mosaic and only used it when had problems Students had a much stronger understanding of NMR interpretation

Texas Lutheran University NMR Mosaic: Key Features Requires use of Integration, Multiplicity, and Chemical Shift Accentuates students’ interpretation errors Eases interpretation of complex multiplets Reinforces relationship between multiplicity and connectivity Can be used with thousands of spectra EMPHASIZES UNDERSTANDING AND PROBLEM SOLVING SKILLS