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Lecture 5

Lecture 5. HDI More Sample Problems (NMR & IR) Due: Lecture Problem 3. HDI: A Tool for Unknown Determination. When given an unknown’s MF, determine the HDI (hydrogen deficiency index). HDI: Write out the MF of the corresponding alkane (C n H 2n+2 )

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Lecture 5

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  1. Lecture 5 HDI More Sample Problems (NMR & IR) Due: Lecture Problem 3

  2. HDI: A Tool for Unknown Determination • When given an unknown’s MF, determine the HDI (hydrogen deficiency index). • HDI: • Write out the MF of the corresponding alkane (CnH2n+2) • Subtract the given unknown MF from the alkane MF *If there is a nitrogen (N) in the MF, remove an NH before the subtraction. *Disregard an oxygen if it appears in the unknown’s MF *If there’s a halogen, replace the halogen with an H • 3. Divide the number by 2 to give you HDI. • Example: Determine the HDI of a compound whose MF is C8H16. • C8H18 • C8H16 • 2 Thus, HDI = 2/2 = 1 • This means that there may be a ring or a double bond in the molecule.

  3. HDI & Some Possibilities HDI = 1: • One double bond • One ring HDI = 2: • One triple bond • One double bond, one ring HDI = 3: • One triple bond, one ring • One triple bond, one double bond • Two double bonds, one ring • Three rings HDI = 4: • Four double bonds • Two triple bonds • One triple bond, two double bonds • A benzene (phenyl) ring Each p bond has an HDI of 1. Each ring has an HDI of 1.

  4. Solving Spectral Unknown Problems • Determine HDI if MF is given. If not given, then use mass spec data. 2. Evaluate the IR spectrum’s functional group region. Use correlation chart. 3. Evaluate the 1H NMR: • Count the # of signals = # of different types of H’s • Look at the ppm values; use correlation chart. Start by looking downfield (ArH, CHO, CO2H) c. Look at splitting patterns  pieces of the molecule; J values d. Consider the integration. If integration is greater than 3, must be symmetry • 4. Evaluate the 13C NMR spectrum: • a. Count the # of signals = # of different types of C’s • b. Look at the ppm values; use correlation chart. Start by looking downfield c. If DEPT info is given, determine the different type of carbons

  5. 13C NMR Correlation Chart 1H NMR Correlation Chart

  6. IR Correlation Chart

  7. Sample Problem 3: Determine the structure of this unknown (MF is C8H9Cl)

  8. Sample Problem 4 Propose a structure that is consistent with the following data: C7H8O (HDI = 4) 1H NMR: 2.43 ppm (s, 1H) 4.58 ppm (s, 2H) 7.28 ppm (m, 5H) IR: 3350 cm-1 Possible compound(s): Solution: Double check structure. Make sure splitting patterns and ppm values make sense as well as the integration values. Be sure that the number of different atoms matches the MF!

  9. Sample Problem 5 Propose a structure that is consistent with the following data: C3H6O2 (HDI = 1) 1H NMR: 1.27 ppm (t, 3H) 2.66 ppm (q, 2H) 10.95 ppm (s, 1H) IR: 1715 cm-1 3500-3000 cm-1 Possible compound(s):    Solution: Double check structure. Make sure splitting patterns and ppm values make sense as well as integration values. Also, make sure the numbers and types of atoms match the MF!

  10. Sample Problem 6 Propose a structure that is consistent with the following data: C5H10O(HDI = 1) 1H NMR: 1.10 ppm (d, 6H) 2.10 ppm (s, 3H) 2.50 ppm (m, 1H) IR: 1720 cm-1  Solution: Double check structure. Make sure splitting patterns and ppm values make sense as well as integration values. Also, make sure the numbers and types of atoms match the MF!

  11. Sample Problem 7 Handout given in class.

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