Chem 318 Spectroscopy Problem Set

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Chemistry 318
IR, MS, UV, NMR Spectroscopy Problem Set
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Chem 318 Spectroscopy Problem Set

• Introduction
• The problems in this exercise are designed to
  enhance your understanding and use of the basic
  principals of the Spectroscopy tools -
  Ultraviolet/Visual, Mass, and Infrared from the
  Chem 315 course and NMR from the Chem 318 course.
  The problems are divided into two types
• Basic concepts of 1H1 (Proton) and 13C6 NMR
  including Chemical Shift, Peak Area Integration,
  Spin-Spin Splitting, and the impact of
  Electronegative groups and Electrophilic Aromatic
  Substitution on Chemical Shift.
• Use of Ultraviolet/Visual, Mass, Infrared,
  1H1NMR, 13C6 NMR spectra and Partial Elemental
  Analysis to determine the structure and identity
  of compounds. The emphasis on these problems is
  the ability of the student to organize and
  present a logical process leading to the
  structure and identification of the compound.
• Presentation
• Where appropriate, the answers should be typed,
  using complete sentences.
• Compound structures may be hand written or you
  can use a drawing program.
• Resources
• Consult the Lab Manual (Slayden, et al.) and the
  lab textbook (Pavia, et al.).
• Slayden P. 29 37
• Pavia NMR P. 909 964
• IR P. 873 909
• Mass P. 964 984
• In the lab manual section, Spectroscopy I, there
  is a section titled Using on-line Databases to
  Help Solve Organic Chemistry Spectroscopy
  Problems. You should review this section so you
  can effectively use the on-line sources to help
  you analyze the problem spectra and to provide a
  source for literature spectra.
• http//classweb.gmu.edu/chemlab/
  (provides access to
  the following)
• http//www.chem.uni-potsdam.de/tools/index.html
  (Spectroscopy Tools
  Wizard)
• http//riodb01.ibase.aist.go.jp/sdbs/cgi-bin/di
  rect_frame_top.cgi (IR, NMR, Mass Spectra)
• http//webbook.nist.gov/chemistry
  
  (Substructure Searches)
• The following website is useful to verify
  Chemical Physical Properties

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Chem 318 Spectroscopy Problem Set
Section A.
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Chem 318 Spectroscopy Problem Set
Section A. (Cont)
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Chem 318 Spectroscopy Problem Set

• Section A (Cont)
• The area under a 1H1 NMR signal is proportional
  to the number of protons generating that
  particular chemical shift. The number of peaks,
  i.e., the multiplet, for a given signal is a
  function of the number of protons attached to the
  carbon atoms adjacent to the Carbon atom
  producing the multiplet. The NMR instrument
  electronically measures the integral area over
  the entire signal, incorporating the multiplet
  peaks. A stairstep is produced on the chart for
  each signal. The height of the stairstep is
  proportional to the area of the signal.Measure
  the height of each of the four (4) stairsteps on
  the following NMR chart and determine the number
  of protons on each Carbon atom. Show your
  calculations.

Answer
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Chem 318 Spectroscopy Problem Set

• Section B Spectral Problems
• Each following problem consists of two or more
  spectra Infrared, Proton 1H1 NMR, 13C6 NMR,
  Mass, UV/Visual.
• For some spectra there is also provided a Partial
  Elemental Analysis (see hints on completing a
  Partial Elemental Analysis on the following page.
• The task of the student is to label and evaluate
  the spectra, complete the elemental analysis, and
  then produce a logical set of arguments leading
  to conclusions as to the identity and structure
  of the compound in question. Simply listing
  absorptions and structural fragments does not
  explain how and why the fragments fit together to
  form the compound. The following steps should be
  followed
• On each IR NMR spectrum, neatly label the major
  absorption peaks with the structural fragment or
  functional group that causes the absorption.
• On the answer template page
• This page must be typed as much as possible
• Evaluate the Mass Spectrum
• Molecular Weight
• Halogens
• Nitrogen
• Complete the Partial Elemental Analysis and
  Determine the Molecular Formula. Note The mass
  spectrum can provide important information
  concerning the elemental makeup of the compound.
• Evaluate the significance of the UV/Visual
  spectra, i.e., what information does the Molar
  Absorptivity Coefficient (Log ?) provide.
• Evaluate the absorptions provided from the IR
  spectrum.
• Evaluate the signals provided from the 1H1 NMR
  and/or 13C NMR spectra.
• Chemical Shifts relative to Electronegativity
• Fragment structures implied from splitting
  patterns
• Analysis of Stairsteps to determine number of
  protons on a given Carbon atom generating the
  signal.
• Utilize the above results to build logical
  arguments leading to the identity of the
  compound.

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Chem 318 Spectroscopy Problem Set
Section B Spectral Problems

• Partial Elemental Analysis
• For some problems you are given a Partial
  Elemental Analysis from which you can calculate
  the Molecular Formula.
• The Elemental Analysis usually provides the C
  Hydrogen in the compound.
• Your task is to complete the analsysis and fill
  in the remaining elements in the compound
  (oxygen, nitrogen, halogens chlorine, bromine)
• The number of atoms, n, of a particular element X
  (C,H,N,Cl, Br) in a compound can be obtained from
  the analysis data using the following equation
• The Relative Molcular Mass (RMM) of each compound
  in the set is given by the m/z value of the
  Molecular Ion, M, in the Mass Spectrum.
• The RAM is the relative atomic mass of each
  element (C-12.01, H-1.008, O-16.00l N-14.01,
  Cl-35.47, Br-79.9).
• Once the number of each of the elements C, H, N
  has been calculated, the other elements present
  can be deduced from compound molecular weight
  (RMM) and total partial mass of the known
  elements C, H, N - in the compound. This can be
  done even if the Nitrogen is not known.
• Once the Molecular Formula of the compound is
  known, the following equation can be used to
  calculate the number of units of unsaturation
  (or units of hydrogen deficiency or double
  bond equivalents) UU, in the molecule.
• Where n4 the number of tetravalent atoms
  present, e.g., Carbon
• n3 the number of trivalent atoms
  present, e.g., Nitrogen
• n1 the number of monovalent ions
  present, e.g., Hydrogen

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Chem 318 Spectroscopy Problem Set

• Section B Spectroscopy Problems (Cont)
• Provide a detailed set of arguments to deduce an
  identity and structure consistent with the
  following 1H1 NMR spectrum. Hint Chemical Shifts
  are influenced by the proximity of
  Electronegative elements within the compound.

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Chem 318 Spectroscopy Problem Set

• Section B Spectroscopy Problems (Cont)
• Provide a detailed set of arguments to deduce an
  identity and structure consistent with the
  following 1H1 and 13C6 NMR spectra. Hint
  Integral values are relative numbers. Also note
  four (4) 13C6 signals.

1H1
13C6
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont)
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont) 3.
Spectra
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont)
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont) 4.
Spectra
88 (M) Missing
Multiplet (quartet nonet)
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont)
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Chem 318 Spectroscopy Problem Set

• Section B Spectroscopy Problems (Cont)
• Spectra

Use staircase values to compute area
integration values, ie. number of protons
generating signal.
quartet
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont)
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Chem 318 Spectroscopy Problem Set

• Section B Spectroscopy Problems (Cont)
• Spectra

M
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Chem 318 Spectroscopy Problem Set
Section B Spectroscopy Problems (Cont)
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Chem 318 Spectroscopy Problem Set

• Section B Spectroscopy Problems (Cont)
• Spectra

1500
1000
3000
2000
Mol Ion Peak M Missing Compound contains C, H,
N, O
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2
2
Sextet