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Doc Brown's Chemistry  Molecular structure deduction

3 problems to solve

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INDEX of all ir, mass, 1H and 13C NMR spectroscopy pages

NMR problem solving with associated molecular data

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A level Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses)

These questions illustrate how you can unite various sources of data-information to deduce the structure of a molecule

You will need tables of nmr chemical shifts and

characteristic infrared absorption frequencies (as wavenumber cm-1)

Atomic masses: C = 12, H = 1, O =16  *  Answers to NMR problems


NMR PROBLEM 1 with associated infrared spectrum, molecular ion and % element by mass data

nmr problem 1 % mass element analysis:

82.76% C and 17.24% H

Infrared spectrum:

Peaks in 2850-2950 cm-1 region

NO suggestion of any specific functional group absorption

Molecular ion peak from mass spectrometry: 58

 

NMR PROBLEM 2 with associated infrared spectrum, molecular ion and % element by mass data 

nmr problem 2 % mass element analysis:

54.55% C, 9.09% H and 36.36% O

Infrared spectrum:

sharp strong absorption at 1735-1750 cm-1

NO broad absorption band from ~2500-3200 cm-1

Molecular ion peak from mass spectrometry: 88

 

NMR PROBLEM 3 with associated infrared spectrum, molecular ion and % element by mass data

nmr problem 3 % mass element analysis:

62.07% C, 10.34% H and 27.59% O

Infrared spectrum:

strong sharp absorption at 1700-1725 cm-1

moderate, broad absorption at ~2450-3150 cm-1

Molecular ion peak from mass spectrometry: 116
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