NMR

• What are the two main types of NMR spectroscopy?

  13C NMR and 1H NMR
• Why is 13C NMR spectra simpler than 1H NMR?

  There is only around 1% C13 in organic molecules
• How many signals are there for equivalent carbon atoms in a C13 NMR spectrum?

  One signal for each set of equivalent C atoms
• What is the relationship between equivalent hydrogen atoms and 1H NMR spectrum signals?

  • One signal for each set of equivalent H atoms
  • Intensity of each signal is proportional to the number of equivalent H atoms
• How many groups of different hydrogen atoms does ethanol have?

  Three groups of different hydrogen atoms
• What is the integration value in 1H NMR spectrum?

  It represents the number of equivalent H atoms
• What is the ratio of equivalent H’s in ethanol?

  3:1:2
• What type of solvents are used in NMR spectroscopy?

  Inert solvents with no 1H atoms
• Why are solvents like CCl4 and CDCl3 used in NMR?

  They have no H atoms to give peaks
• What is added to the sample to calibrate the NMR spectrum?

  A small amount of TMS
• Why is TMS used for calibration in NMR?

  It only gives one signal and is inert
• What does the chemical shift (δ) measure in NMR?

  How much the field has shifted from TMS
• What does a higher electronegativity of nearby groups do to the δ value?

  It gives a greater shift in the δ value
• What type of hydrogen usually appears as singlets in 1H NMR spectra?

  Hydrogens bonded to nitrogen or oxygen
• How does spin-spin coupling affect peak splitting in 1H NMR?

  It splits peaks based on neighboring inequivalent H’s
• What is the process to determine the empirical formula from elemental analysis?

  1. Divide percentage by atomic mass
  2. Find the simplest whole number ratio
  3. Write the empirical formula
• What is the molecular ion peak m/z value used for?

  To determine the molecular formula
• How can IR spectra help identify functional groups?

  By looking for specific bond absorptions
• What does a singlet in NMR indicate about neighboring hydrogens?

  It is next to a carbon with no H’s
• What does a triplet in NMR indicate about neighboring hydrogens?

  It is next to a carbon with 2 H’s
• What does a quartet in NMR indicate about neighboring hydrogens?

  It is next to a carbon with 3 H’s
• How do you interpret NMR spectra to determine the structure of a compound?

  1. Identify the number of peaks for environments
  2. Analyze integration values for H counts
  3. Determine splitting patterns for neighboring H’s
  4. Combine data with IR and mass spectra
• What is the empirical formula of a compound with C 66.63%, H 11.18%, O 22.19%?

  C4H8O
• How do you find the molecular formula from the empirical formula?

  Use the molecular ion peak m/z value
• What does the presence of a C=O bond and absence of O-H indicate?

  The compound is likely an ester
• What does a peak at δ 4 in NMR indicate?

  H–C–O environment
• What does a singlet of area 9 in NMR suggest?

  Presence of 3 CH3 groups
• How do you determine the final structure of a compound from NMR data?

  Combine all peak data to deduce structure
• What is the final structure of the compound with empirical formula C4H8O and molecular formula C8H16O2?

  • C
  • CH3
  • C
  • H3
  • CH3
  • CH2
  • C
  • O
  • O
  • CH2
  • CH3